What is a material point in physics. Material point, solid. Relationship with real objects

When solving a whole set of tasks can be distinguished from the shape and size of the body and consider it as a material point.

Definition

Material point In physics, they call a body having a mass, but the sizes of which, in comparison with distances to other bodies, can be neglected in the problem under consideration.

The concept of "material point"

The concept of "material point" is an abstraction. There are no material points in nature. But setting some problems of mechanics makes it possible to use this abstraction.

When we talk about point in kinematics, it can be viewed as a mathematical point. In kinematics, under the point it means a small label on the body or the body itself, if its dimensions are small in comparison with those distances that the body overcomes.

In this section of mechanics, like dynamics, you need to talk about a material point as a point that has a mass. The main laws of classical mechanics belong to the material point, the body that does not have geometric sizes, but has a lot.

In dynamics, the size and shape of the body in many cases does not affect the nature of the movement, in this case the body can be viewed as a material point. But in other conditions, the same body of the point cannot be considered, since its form and size turn out to be decisive in the description of the body movement.

So, if a person interests how much time you need to car to get from Moscow to Tyumen, it is not necessary to know how everyone moves from the wheels. But, if the motorist is trying to squeeze his car on a narrow parking space, it is impossible to take the car for the material point, as the size of the car is important. You can take the land for the material point, if we consider the movement of our planet around the Sun, but you can't do that, when studying her movement around your own axis, if we are trying to establish the reasons why the day replaces the night. So, the same body in some conditions can be viewed as a material point, in other conditions it is impossible to do this.

There are some types of movement in which the body can be safely taken for the material point. For example, with the proposed solid movement, all parts of it move the same, therefore, in such a movement, the body is usually considered as a point with a mass that is equal to the mass of the body. But if the same body revolves around his axis, it is impossible for the material point.

And so, the material point is the simplest model of the body. If the body can be like a material point, it significantly simplifies the solution to the task of studying its movement.

Different types of traffic are distinguished, first of all, by the appearance of the trajectory. In the event that the trajectory movement of the point is the straight line, then the movement is called straightforward. In relation to the movement of the macroscopic body, it makes sense to talk about the straight or curvilinear body movement only when it is possible when describing the motion, it is limited to considering the movement of one point of this body. At the body, in general, different points can make different types of movement.

System of material points

If the body can not be taken for the material point, it can be represented as a system of material points. In this case, the body is mentally divided into infinitely small elements, each of which can be taken for the material point.

In the mechanics, each body can be represented as a system of material points. Having the traffic laws, we can assume that we have a method for describing any body.

In mechanics, a significant role is played by the concept of an absolutely solid body, which is defined as a system of material points, the distances between which are unchanged, with any interactions of this body.

Examples of tasks with the solution

Example 1.

The task. In which case, the body can be considered a material point:

The athlete at the competition throws the core. Core can be considered a material point?

The ball rotates around its axis. The ball is the material point?

Gymnast performs an exercise on the bars.

The runner overcomes the distance.

Example 2.

The task. Under what conditions moving up the stone can be considered a material point. See Fig. 1 and Fig.2.

Decision: In fig. 1 The dimensions of the stone can not be considered small in comparison with the distance to it. In this case, the stone can not be considered a material point.

In fig. 2 Stone rotates, therefore, it cannot be considered a material point.

Answer. The stone thrown up can be considered a material point if its dimensions are small in comparison with the distance to it, and it will move progressively (there will be no rotation).

Definition

A material point is a macroscopic body, dimensions, shape, rotation and internal structure of which can be neglected when describing its movement.

The question of whether this body can be considered as a material point depends not on the size of this body, but on the conditions of the problem being solved. For example, the land radius is significantly less than the distance from the ground to the Sun, and its orbital movement can be well described as a motion of a material point with a mass equal to the mass of the Earth and located in its center. However, when considering the daily movement of the earth around its own axis, its material point does not make sense. The applicability of the material point model to a particular body depends not as much on the size of the body itself, as from the conditions of its movement. In particular, in accordance with the theorem on the movement of the center of the mass of the system in progressive movement, any solid body can be considered a material point, the position of which coincides with the center of mass body.

Mass, position, speed and some other physical properties of the material point at each specific point in time fully determine its behavior.

The position of the material point in space is defined as the position of the geometric point. In classical mechanics, the mass of the material point relies constant in time and independent of any characteristics of its movement and interaction with other bodies. With an axiomatic approach to the construction of classical mechanics, the following is taken as one of the axis:

Axiom

The material point is a geometric point, which is put in line with a scalar called mass: $ (R, M) $, where $ R $ is a vector in the Euclidean space, referred to any decartian coordinate system. The mass relies on a constant, independent of the point of point in space, without time.

Mechanical energy can be stacked with a material point only in the form of the kinetic energy of its movement in space and (or) the potential energy of interaction with the field. This automatically means the inability of the material point to deformities (the material point can only be called an absolutely solid body) and the rotation around its own axis and changes in the direction of this axis in space. At the same time, the model of the body moved, described by the material point, which consists in changing its distance from some instantaneous center of rotation and two Euler angles, which set the direction of the line connecting this point with the center, is extremely widely used in many sections of mechanics.

The method of studying the laws of movement of real bodies by studying the movement of the ideal model - material point - is the main in the mechanics. Any macroscopic body can be represented as a totality of interacting material points G, with masses equal to the masses of its parts. The study of the movement of these parts is reduced to the study of the movement of material points.

The limited application of the concept of the material point is visible from this example: in a rarefied gas at high temperature, the size of each molecule is very small compared to the typical distance between molecules. It would seem that they can be neglected and considered a material point molecule. However, this is not always the case: oscillations and rotation of the molecule - an important tank of "internal energy" of the molecule, the "capacity" of which is determined by the dimensions of the molecule, its structure and chemical properties. In a good approximation, as a material point, it is sometimes possible to consider a monoomic molecule (inert gases, pairs of metals, etc.), but even in such molecules at a sufficiently high temperature there is an excitation of electron shells due to collisions of molecules, followed by highlighting.

Exercise 1

a) a car entering the garage;

b) Car on the track Voronezh - Rostov?

a) the car entering the garage cannot be taken for the material point, since the dimensions of the vehicle are essential;

b) The car on the highway Voronezh Rostov can be taken for the material point, since the size of the car is much less than the distance between the cities.

Is it possible to take for the material point:

a) a boy who, on the way from school, goes 1 km;

b) Boy doing charging.

a) When the boy, returning from school, goes to the house a distance of 1 km away, then the boy in this movement can be viewed as a material point, because its dimensions are small compared to the distance he passes.

b) When the same boy performs the exercises of the morning charging, then it is impossible to consider the material point.

Material point

Material point (Particle) - the simplest physical model in the mechanics is the perfect body whose sizes are zero, you can also count the sizes of the body are infinitely small compared to other sizes or distances within the assuming tasks under study. The position of the material point in space is defined as the position of the geometric point.

Practically under the material point understands the body weight, size and form of which can be neglected when solving this task.

With the straight-line movement of the body, one coordinate axis is enough to determine its position.

Features

The mass, position and speed of the material point at each specific point in time fully determine its behavior and physical properties.

Corollary

Mechanical energy can be stacked with a material point only in the form of the kinetic energy of its movement in space, and (or) the potential energy of interaction with the field. This automatically means the inability of the material point to deformities (the material point can only be called an absolutely solid body) and the rotation around its own axis and changes in the direction of this axis in space. At the same time, the model of the body moved, described by the material point, which consists in changing its distance from some instantaneous center of rotation and two Euler angles, which set the direction of the line connecting this point with the center, is extremely widely used in many sections of mechanics.

Restrictions

Notes

Wikimedia Foundation. 2010.

Mechanical movement
Absolutely solid body

Watch what is a "material point" in other dictionaries:

MATERIAL POINT - point having a lot. In the mechanics, the material point is used in cases where the sizes and shape of the body do not play roles when studying its movement, but only mass is important. Almost any body can be viewed as a material point if ... ... Big Encyclopedic Dictionary

MATERIAL POINT - The concept administered in the mechanics to designate the object, is considered as a point having a mass. The position of M. t. In Pré is defined as the position of the geom. Points that significantly simplifies the solution of the problems of mechanics. Practically body can be considered ... ... Physical encyclopedia

material point - point that has a mass. [Collection of recommended terms. Issue 102. Theoretical mechanics. Academy of Sciences of the USSR. Committee of Scientific Technical Terminology. 1984] Themes Theoretical Mechanics En Particle De Materialle Punkt FR Point Matériel ... Technical translator directory

MATERIAL POINT Modern encyclopedia

MATERIAL POINT - In the mechanics: an infinitely small body. A dictionary of foreign words included in the Russian language. Chudinov A.N., 1910 ... Dictionary of foreign words of the Russian language

Material point - The material point, the concept administered in the mechanics to designate the body, the dimensions and the form of which can be neglected. The position of the material point in space is defined as the position of the geometric point. The body can be considered material ... ... Illustrated Encyclopedic Dictionary

material point - The concept administered in the mechanics for the object of infinitely small sizes having a mass. The position of the material point in space is defined as the position of the geometric point, which simplifies the solution of the mechanics problems. Virtually any body can ... ... encyclopedic Dictionary

Material point - geometric point with mass; Material dot abstract image of a material body, having a mass and having no size ... The start of modern natural science

material point - Materialusis Taškas Statusas T Sritis Fizika Atitikmenys: Angl. Mass Point; Material Point Vok. Massenpunkt, m; Materieller Punkt, M Rus. material point, f; Point mass, F pranc. Point Masse, m; Point Matériel, M ... Fizikos Terminų žodynas

material point - point having a lot of ... Polytechnic Terminology Dictionary

Books

Set of tables. Physics. Grade 9 (20 tables) ,. An academic album of 20 sheets. Material point. Coordinates of a moving body. Acceleration. Newton's laws. The law of global gravity. Straight and curvilinear movement. Body Movement

The mechanical movement of the body is called a change in its position in space relative to other bodies over time. He is studying the movement of the bodies of the mechanic. The movement of an absolutely solid (not deforming when moving and interaction), in which all of its points at the moment is moving equally, is called a translational movement, it is necessary to describe the movement of one point of the body. The movement in which the trajectories of all points of the body are circles with the center on one straight line and all the planes of the circles are perpendicular to this direct, called the rotational motion. The body, form and sizes of which can be neglected in these conditions, is called a material point. This is negligible

value is permissible to be done when the sizes of the body are small compared to the distance it passes or the distance of this body to other bodies. To describe the movement of the body, you need to know its coordinates at any time. This is charged the main task of mechanics.

2. The relativity of motion. Reference system. Units.

To determine the coordinates of the material point, you must select the reference body and associate the coordinate system with it and set the start of time. The coordinate system and indication of the start of the timing of the time form a reference system relative to which the body movement is considered. The system should move with the postcant rate (or rest, which generally speaking the same thing). The trajectory of the body movement, passed path and movement - depend on the selection of the reference system, i.e. Mechanical movement relative. The length of the length of length is a meter equal to the distance, the light in vacuo in a second. Second - the unit of measurement of time is equal to the radiation period of the Cesium-133 atom.

3. Trajectory. Path and movement. Instant speed.

The body trajectory is called the line described in the space moving material. The path is the length of the trajectory area from the initial to the final movement of the material point. Radius vector - vector connecting the origin and point of space. Movement - vector connecting the initial and endpoint of the trajectory site trained during the time. Speed \u200b\u200bis a physical value that characterizes the speed and direction of movement at a given time. The average speed is defined as. The average track speed is equal to the path of the path passed by the body over the time interval to this gap. . Instant speed (vector) - the first derivative of the radius-vector moving point. . Instant speed is aimed at tangent to the trajectory, medium - along the secant. Instant track speed (scalar) - the first derivative of the path in time, in size is equal to instantaneous speed

4. Uniform rectilinear movement. Graphs of the dependence of kinematic values \u200b\u200bfrom time in uniform movement. Addition speeds.

Movement with a constant modulo and direction is called uniform straightforward movement. With uniform rectilinear movement, the body passes the same distances in any equal intervals. If the speed is constant, then the path passed is calculated as. The classic rate of addition of speeds is formulated as follows: The motion speed of the material point with respect to the reference system taken for the fixed, is equal to the vector sum of the speed of the movement of the point in the movable system and the movement speed of the mobile system relatively fixed.

5. Acceleration. Equal asked rectilinear movement. The graphs of the dependence of the kinematic quantities from time to the equilibrium movement.

Movement in which the body for equal intervals of time performs unequal movements, is called uneven movement. With uneven progressive movement, the body speed varies over time. Acceleration (vector) is a physical value that characterizes the speed of changing the speed of the module and in the direction. Instant acceleration (vector) is the first time derivative of time. . Alternatively called movement with acceleration, permanent module and direction. The speed with an equilibrium movement is calculated as.

From here the formula for the path with an equilibrium movement is displayed as

Also, the formulas derived from the speed equations and the path with an equilibrium movement.

6. Free drop body. Acceleration of gravity.

Falling the body is called his movement in the field of gravity (???) . The drop in the bodies in vacuo is called a free drop. It is experimentally established that when the body is free, the same is moved equally regardless of its physical characteristics. Acceleration with which the body falls into the Earth is called the acceleration of free fall and is indicated

7. Uniform movement around the circumference. Acceleration with uniform body movement around the circle (centripetal acceleration)

Any movement on a sufficiently small portion of the trajectory is possible to approximately consider as a uniform movement around the circumference. In the process of uniform movement around the circle, the speed value remains constant, and the direction of the velocity vector changes.<рисунок>.. The speed of acceleration when driving around the circle is directed perpendicular to the velocity vector (directional by tangent), to the center of the circle. The period of time for which the body makes a complete turn around the circumference is called a period. . The value, reverse period, showing the number of revolutions per unit of time, is called frequency. Applying these formulas, it can be output that, or. Angular speed (rotational speed) is defined as . The angular velocity of all points of the body is the same, and characterizes the movement of the rotating body as a whole. In this case, the linear velocity of the body is expressed as, and acceleration - like.

The principle of independence of movements is considering the movement of any point of the body as the sum of two movements - progressive and rotational.

8. The first Newton law. Inertial reference system.

The phenomenon of preserving the velocity of the body in the absence of external influences is called inertia. The first law of Newton, he is the law of inertia, says: "There are reference systems that relative to which progressively moving bodies retain their speed constant if other bodies do not act on them." The reference system relative to which the bodies in the absence of external influences are moving straight and evenly called inertial reference systems. The reference systems associated with the Earth is considered inertial, subject to neglect of the rotation of the Earth.

9. Mass. Force. The second law of Newton. Addition of forces. Center of gravity.

The reason for changing the body of the body is always its interaction with other bodies. The interaction of two bodies always change speeds, i.e. Acceleration is purchased. The ratio of the accelerations of the two bodies is equally with any interactions. The body property, on which its acceleration depends when interacting with other bodies is called inertia. Quantitative measure of inertness is the mass of the body. The ratio of mass of interacting bodies is equal to the reverse ratio of the acceleration modules. The second law of Newton establishes the relationship between the kinematic characteristic of motion - acceleration, and the dynamic characteristics of interaction - forces. , or, more precisely,, i.e. The rate of change of the pulse of the material point is equal to the power acting on it. With a simultaneous action on one body of several forces, the body moves with an acceleration that is a vector amount of accelerations that would arise when exposed to each of these forces separately. The forces applicable to one point applied to the rule of the formation of vectors. This provision is called the principle of independence of the forces. The center of the masses is such a point of a solid or a system of solid bodies, which moves the same as the material point of mass equal to the sum of the masses of the entire system as a whole, to which the same resulting force acts on the body. . Integrating this expression in time, you can get expressions for the coordinates of the center of mass. The center of gravity is the point of an application of an equally all gravity of gravity acting on particles of this body at any position in space. If the linear sizes of the body are small compared to the size of the Earth, the center of the masses coincides with the center of gravity. The sum of the moments of all elementary gravity forces relative to any axis passing through the center of gravity is zero.

10. The third Newton law.

With any interaction of the two bodies, the ratio of the modules of acquired accelerations is constantly equal to the inverse relationship of the masses. Because In the interaction of bodies, the speeds of accelerations have the opposite direction, you can record that . According to Newton's second law, the force acting on the first body is equal to the second. In this way, . The third Newton law binds the strength with which the bodies act on each other. If two bodies interact with each other, the forces arising between them are applied to different bodies are equal in size, opposite to the direction, act along one straight line, have the same nature.

11. Elasticity forces. The law of a bitch.

The force arising from the deformation of the body and directed to the side opposite to the movements of the particles of the body with this deformation is called the force of elasticity. Experiments with the rod have shown that at small deformations compared to the size of the body, the modulus of the elasticity force is directly proportional to the module of the vector of moving the free end of the rod, which in the projection looks like. This connection was established by the R.GUK, its law is formulated as: the force of elasticity arising during deformation of the body is proportional to the elongation of the body to the side opposite to the direction of movement of the body particles during deformation. Coefficient k. It is called the rigidity of the body, and depends on the shape and material of the body. It is expressed in Newton on the meter. The strengths of elasticity are due to electromagnetic interactions.

12. Friction forces, sliding friction coefficient. Viscous friction (???)

The force arising at the border of the interaction of bodies in the absence of a relative movement of bodies is called peace friction force. The friction force of rest is equal to the outer force module, aimed at tangent of the surface of contacting the bodies and opposite to it in the direction. With the uniform movement of one body on the surface of another, under the influence of external force on the body, an force is valid for the module of the driving force and the opposite direction. This force is called the force of friction. Slip friction strength vector is aimed against velocity vector, so this force always leads to a decrease in the relative velocity of the body. The friction forces also, as well as the strength of elasticity, have electromagnetic nature, and arise due to the interaction between the electrical charges of atoms of contacting bodies. It is experimentally established that the maximum value of the module of the friction force of rest is proportional to the power of pressure. Also are approximately equal to the maximum value of the friction force of the rest and the coefficient of sliding, as approximately equal to the proportionality coefficients between the friction forces and the body pressure on the surface.

13. Gravitational forces. The law of global gravity. Gravity. Body weight.

From the fact that the bodies regardless of their mass fall with the same acceleration, it follows that the force acting on them is proportional to the mass of the body. This force of attraction, acting on all bodies from the ground, is called heavy gravity. Gravity force valid at any distance between the bodies. All bodies are attracted to each other, the world's strength is directly proportional to the mass of the masses and is inversely proportional to the square square between them. The vectors of the world's strengths are directed along a straight line connecting mass centers. , G is gravitational constant, equal. The body weight is called the force with which the body due to gravity acts on the support or stretches the suspension. The weight of the body is equal to the module and is opposite to the direction of the elasticity of support according to the third law of Newton. According to Newton's second law, if no power has no strength on the body, the body's gravity is equalized by elasticity. As a result, the body weight on a fixed or evenly moving horizontal support is equal to the strength of gravity. If the support is moving with acceleration, then on the second Newton law Where is displayed. This means that the weight of the body, the direction of acceleration of which coincides with the direction of acceleration of the free fall, is less than the weight of the rest of the bodily.

14. Body movement under the action of gravity vertically. Movement of artificial satellites. Weightlessness. First cosmic speed.

When throwing the body parallel to the earth's surface, the flight distance will be the greater the larger the initial speed. At high speed values, it is also necessary to take into account the shag-formation of the Earth, which is reflected in the change in the direction of the gravity vector. At a certain value of speed, the body can move around the Earth under the action of the world's strength. This speed, called the first cosmic, can be determined from the equation of the body movement around the circle. On the other hand, from the Second Law of Newton and the World of World, it follows that. Thus, at a distance R. from the center of the celestial body mass M. The first cosmic speed is equal. When changing the body of the body, the shape of its orbit from the circle on the ellipse is changing. When the second cosmic speed is reached, an orbit becomes parabolic.

15. Body impetus. The law of preserving the impulse. Jet propulsion.

According to the second law of Newton, regardless of whether the body was in peace or moved, the change in its speed can occur only when interacting with other bodies. If on the body mass m. for a time t. There is a force and the speed of its movement varies from before, then the acceleration of the body is equal. Based on the second law of Newton, it can be written for strength. The physical value equal to the work of force at the time of its action is called a power pulse. The pulse of force shows that there is a magnitude equally changing in all bodies under the influence of the same forces if the time of force is equally equally. This value equal to the product of the body mass on the speed of its movement is called a body pulse. The change in the body pulse is equal to the impulse of force, which caused this change. Time two bodies, masses and moving with speeds and. According to the third law of Newton, the forces acting on the bodies in their interaction are equal to the module and are opposite to the direction, i.e. They can be denoted as. For changes in pulses, when interacting can be recorded. From these expressions, we get that That is, the vector sum of the two-bodies pulses before the interaction is equal to the vector sum of pulses after interaction. In a more general form, the impulse conservation law sounds like this: if, then.

16. Mechanical work. Power. Kinetic and potential energy.

Work BUT A constant force is called a physical value equal to the product of the modules of force and movement multiplied by the cosine of the angle between vectors and. . The work is a scalar value and can have a negative value if the angle is between the venosions and the forces more. The unit of work is called Joule, 1 Joule is equal to the work performed by force in 1 Newton while moving the point of its application by 1 meter. Power is a physical value equal to the ratio of work by a period of time during which this work was performed. . The power is called watt, 1 watt is equal to the power at which work in 1 joule is performed in 1 second. Suppose that there is a mass m. There is a force (which can generally be the resultant of several forces), under the action of which the body moves on in the direction of the vector. The power module on the second Newton law is equal mA., and the movement vector module is associated with acceleration and initial and end speeds as. From here to work it turns out the formula . The physical value equal to half the product of body mass per square rate is called kinetic energy. The work of the equal forces applied to the body is equal to the change in kinetic energy. The physical value equal to the product of the body mass on the free fall acceleration module and the height to which the body is raised above the surface with zero potential is called the potential energy of the body. The change in potential energy characterizes the work of gravity for the movement of the body. This work is equal to the change in the potential energy taken with the opposite sign. The body located below the surface of the Earth has a negative potential energy. Potential energy have not only raised bodies. Consider the work performed by the strength of elasticity during the deformation of the spring. The force of elasticity is directly proportional to the deformation, and its average value will be equal , work is equal to the work of force for deformation , or . The physical value equal to half the product of body rigidity per square deformation is called the potential energy of the deformed body. An important characteristic of potential energy is that the body cannot have it, without interacting with other bodies.

17. The conservation of energy conservation in the mechanics.

Potential energy characterizes the interacting bodies, kinetic - moving. Both, and the other arise as a result of interaction tel. If several bodies interact with each other by the forces and elasticity forces, and no external forces on them act (or their relative is zero), then with any interactions, the work of the strength of elasticity or the forces of grave is equal to the change in potential energy taken with the opposite sign . At the same time, according to the theorem on kinetic energy (the change in the kinetic energy of the body is equal to the work of external forces) the work of the same strength is equal to the change in the kinetic energy. . From this equality it follows that the sum of the kinetic and potential energies of the bodies constituting the closed system and interacting with each other forces and elasticity remains constant. The sum of the kinetic and potential energies of bodies is called complete mechanical energy. The complete mechanical energy of a closed system of bodies interacting with each other forces and elasticity remains unchanged. The work of the forces of gravity and elasticity is equal to, on the one hand, an increase in kinetic energy, and on the other hand, a decrease in potential, that is, the work is equal to the energy that has turned from one species to another.

18. Simple mechanisms (inclined plane, lever, block) their use.

The inclined plane is used to make the body of a large mass can be moved by the action of force, significantly lower body weight. If the angle of the inclined plane is equal, then to move the body along the plane it is necessary to apply force equal to. The ratio of this force to the weight of the body with the disregard of friction force is equal to the sinus of the angle of the plane. But when I wanted in force there is no winning in the work, because The path increases at times. This result is a consequence of the law of conservation of energy, since the work of gravity does not depend on the lifting trajectory.

The lever is in equilibrium if the moment of forces rotating it clockwise is equal to the moment of illumination, rotating the lever counterclockwise. If the directions of the forces of the forces applied to the lever are perpendicular to the shortest direct connecting of the application points and the axis of rotation, the equilibrium conditions take the form. If, the lever provides a winnings. Winning in force does not give a win in the work, because When turning at an Angle A force makes work, and the force makes work. Because by condition, then.

The block allows you to change the direction of force. The shoulders of the forces attached to different points of the fixed block are the same, and therefore the winning power of the fixed block does not give. When lifting the cargo with the help of a mobile unit, the winnings are in force twice, because The shoulder of gravity twice the shoulder of the cable tension force shoulder. But when stretching the cable for the length l. load rises to height l / 2.Therefore, the fixed block also does not give a win in the work.

19. Pressure. Pascal law for liquids and gases.

The physical value equal to the ratio of the force module acting perpendicular to the surface to the area is the surface, is called pressure. Pressure unit - Pascal, equal to pressure produced by force in 1 Newton to an area of \u200b\u200b1 square meter. All fluids and gases transmit pressure produced on them all directions.

20. Reporting vessels. Hydraulic Press. Atmosphere pressure. Bernoulli equation.

In the cylindrical vessel, the pressure of pressure on the bottom of the vessel is equal to the weight of the fluid column. Pressure on the bottom of the vessel is equal where the pressure is in depth h. Equally. On the walls of the vessel, the same pressure is valid. Equality of fluid pressure on the same height leads to the fact that in the reporting vessels of any form, free surfaces of the restricted homogeneous fluid are at the same level (in case of neglecting the alms of capillary forces). In the case of an inhomogeneous liquid, the height of the than-dense fluid post will be less height less dense. Based on the law of Pascal, a hydraulic machine works. It consists of two communicating vessels, closed pistons of different areas. The pressure produced by the external force on one piston is transmitted by the law of Pascal to the second piston. . The hydraulic machine gives a gain in strength at as many times as the area of \u200b\u200bits large piston is more small square.

With the stationary movement of the incompressible fluid, the equation of continuity is valid. For an ideal fluid in which you can neglect the viscosity (that is, the friction between its particles) mathematical expression The law of conservation of energy is the Bernoulli equation .

21. Torricelli experience. Changes in atmospheric pressure with a height.

Under the action of gravity, the upper layers of the atmosphere are powered by underlying. This pressure according to the law of Pascal is transferred in all directions. This pressure has the greatest importance at the surface of the Earth, and is due to the weight of the air column from the surface to the atmosphere border. With an increase in height, the mass of the layers of the atmosphere, which are reduced to the surface, therefore, the atmospheric pressure with a height decreases. At the sea level atmospheric pressure is 101 kPa. Such pressure has a mouth of mercury height of 760 mm. If we drop the tube into liquid mercury, in which the vacuum is created, then under the action of atmospheric pressure, mercury will rise in it in such a height, in which the pressure of the fluid column will become equal to an external atmospheric pressure on the open surface of mercury. When the atmospheric change is changed, the height of the fluid column in the tube will also change.

22. Archimedean The power of the day of liquids and gases. Conditions of swimming tel.

The dependence of pressure in fluid and gas from depth leads to the occurrence of the ejecting force acting on any body immersed in liquid or gas. This force is called archimedean power. If the body is loaded into the liquid, then the pressure on the side walls of the vessel is equalized by each other, and the resulting pressures from the bottom and above is the archimedean force. . Forces pushing the body immersed in liquid (gas) is equal to the weight of the liquid (gas) displaced by the body. Archimedean strength is directed oppositely by the power of gravity, so when weighing the body weight in fluid is less than in vacuum. On the body in the liquid, the strength of gravity and the Archimedean force acts. If the strength of gravity in the module is more - the body is sinking, less - pops up, equal - can be in equilibrium of any depth. These relationships are equal to the relationship of body density and liquid (gas).

23. The main provisions of the molecular-kinetic theory and their experienced justification. Brownian motion. Weight and size molecules.

The molecular-kinetic theory is called the doctrine of the structure and properties of the substance using the idea of \u200b\u200bthe existence of atoms and molecules as the smallest particles of the substance. The main provisions of the MKT: The substance consists of atoms and molecules, these particles are chaotically moving, the particles interact with each other. The movement of atoms and molecules and their interaction obeys the laws of mechanics. In the interaction of molecules with their convergence, the forces of attraction prevail. At some distance between them there are repulsive forces that are superior to the module of attraction force. Molecules and atoms make indiscriminate fluctuations regarding the provisions where the strength of attraction and repulsion balance each other. In liquid, the molecule not only fluctuate, but also jump from one equilibrium position to another (fluidity). In the gases of the distance between atoms, much larger than the dimensions of molecules (compressibility and extensibility). R. Browne at the beginning of the 19th century discovered that solid particles are randomly moving in the liquid. This phenomenon could only explain the MTK ,. The randomly moving fluid or gas molecules face a solid particle and change the direction and the speed module of its movement (at the same time, of course, changing and its direction and speed). The smaller the particle sizes are all the more noticeable, the change in the pulse becomes. Any substance consists of particles, so the amount of substance is considered to be proportional to the number of particles. The unit of the amount of substance is called mole. Mol is equal to the amount of substance containing so many atoms as they contain them in 0.012 kg of carbon 12 S. The ratio of the number of molecules to the amount of substance is called constant avhipa: . The amount of substance can be found as the ratio of the number of molecules to the constant Avogadro. Molar mass M. called the value equal to the ratio of the mass of the substance m. to the amount of substance. The molar mass is expressed in kilograms on mole. Molar mass can be expressed through the mass of the molecule m 0. : .

24. Perfect gas. The main equation of the molecular-kinetic theory of perfect gas.

To explain the properties of a substance in a gaseous state, an ideal gas model is used. In this model, the following is assumed: the gas molecules have a negligible size compared with the volume of the vessel, there are no strengths of attraction between molecules, when the vessel should be turned off and the walls of the vessel. A qualitative explanation of the phenomenon of gas pressure is that the molecules of the ideal gas in collisions with the walls of the vessel interact with them as elastic bodies. In the collision of the molecule with the vessel wall, the projection of the velocity vector on the axis perpendicular to the wall changes to the opposite. Therefore, when a collision, the projection is rapid -Mv X. before mV X., and the change in the impulse is equal. During the collision, the molecule acts on the wall with force equal to the third law of Newton by the Silence opposite to the direction. Molecules are very much, and the average value of the geometric sum of the forces acting on the side of individual molecules, and forms gas pressure on the walls of the vessel. Gas pressure is equal to the ratio of the pressure force module to the area of \u200b\u200bthe vessel wall: p \u003d F / S. Suppose gas is located in a cubic vessel. The impulse of one molecule is 2 mV, one molecule affects the wall on average with force 2MV / DT.. Time D. t. movements from one wall of the vessel to another equal 2L / V., hence, . Pressure force on the wall of the vessel of all molecules is proportional to their number, i.e. . Because of the total chaotic movement of molecules, their movement for each of the directions is equally and equal to 1/3 of the total number of molecules. In this way, . Since the pressure is produced on the edge of Cuba Square l 2., the pressure will be equal. This equation is called the main equation of molecular kinetic theory. Designed for the average kinetic energy of molecules, we get.

25. Temperature, its measurement. Absolute temperature scale. Speed \u200b\u200bof gas molecules.

The main MCT equation for perfect gas establishes a link between micro and macroscopic parameters. When contacting two bodies, their macroscopic parameters change. When this change ceased, they say that there was a thermal equilibrium. The physical parameter, the same in all parts of the body of bodies, which are in a state of thermal equilibrium, is called the body temperature. Experiments have shown that for any gas that is in a state of thermal equilibrium, the ratio of pressure on the volume to the amount of molecules is the same . This allows you to take the amount as a measure of temperature. As n \u003d n / v, taking into account the main MKT equation, therefore, the value is equal to two thirds of the average kinetic energy of molecules. where k. - proportionality coefficient depending on the scale. In the left side of this equation, the parameters are non-negative. From here - the gas temperature at which its pressure at a constant volume is zero, is called absolute zero temperature. The value of this coefficient can be found in two known states of a substance with known pressure, volume, number of temperature molecules. . Coefficient k., called the Boltzmann constant, is equal . From the equations of the temperature of the temperature and medium kinetic energy it follows, i.e. The average kinetic energy of the chaotic movement of molecules is proportional to the absolute temperature. . This equation shows that with the same temperature values \u200b\u200band concentration of molecules, the pressure of any gases is equally.

26. The equation of the state of the ideal gas (Mendeleev-Klapairone equation). Isothermal, isochran and isobaric processes.

Using the dependence of pressure from the concentration and temperature, it is possible to find a link between the macroscopic gas parameters - volume, pressure and temperature. . This equation is called the equation of the state of the ideal gas (Mendeleev-Klapairone equation).

The isothermal process is called the process flowing at a constant temperature. From the equation of the state of the ideal gas, it follows that at a constant temperature, mass and composition of the gas, the product of pressure on the volume should remain constant. The graph of isotherm (curved isothermal process) is a hyperbole. The equation is called the law of Boyle Mariotta.

The process proceeding with a constant volume, mass and composition of the gas is called a isoormal process. Under these conditions where is the temperature coefficient of gas pressure. This equation is called the Charles law. The graph of the isochoric process equation is called isochora, and is a direct, passing through the origin of the coordinates.

The isobaric process is called the process flowing at constant pressure, mass and composition of gas. Similarly, as for a isochlorine process, you can get an equation for the isobaric process. . The equation describing this process is called the Gay Loursak law. The graph of the equation of the isobaric process is called the isobar, and is direct, passing through the origin of the coordinates.

27. Internal energy. Work in thermodynamics.

If the potential energy of the interaction of molecules is zero, then the internal energy is equal to the sum of the kinetic energies of the movement of all gas molecules . Consequently, when the temperature of the gas changes and the internal energy of the gas changes. Substituting into the equation for the energy equation of the state of the ideal gas, we obtain that the internal energy is directly proportional to the product of gas pressure to the volume. . The internal energy of the body may vary only when interacting with other bodies. With mechanical interaction of bodies (macroscopic interaction), the measure of transmitted energy is the work BUT. With heat exchange (microscopic interaction), the measure of the transmitted energy is the amount of heat Q.. In the uninsulated thermodynamic system, the change in the internal energy D U. equal to the amount of the transmitted amount of heat Q. and external forces BUT. Instead of work BUTperformed by external forces, it is more convenient to consider work A`committed by the system over external bodies. A \u003d -A`. Then the first law of thermodynamics is expressed as, or. This means that any machine can perform work on external bodies only by receiving the total of heat Q. or reduce internal energy D U.. This law excludes the creation of the first-kind eternal engine.

28. The amount of heat. Specific heat capacity of the substance. The law of conservation of energy in thermal processes (the first law of thermodynamics).

The process of transferring heat from one body to another without performing work is called heat exchange. The energy transmitted by the body as a result of heat exchange is called the amount of heat. If the heat transfer process is not accompanied by work, then on the basis of the first law of thermodynamics. The internal energy of the body is proportional to the mass of the body and its temperature, therefore . Value from It is called specific heat capacity, one -. The specific heat capacity shows how much heat should be transmitted to heating 1 kg of substance per 1 degree. The specific heat capacity is not an unambiguous characteristic, and depends on the operation performed by the body during heat transfer.

In the implementation of heat exchange between two bodies in the conditions of equality zero operation of external forces and in thermal insulation from other bodies, according to the law of energy conservation . If the change in internal energy is not accompanied by work, then, or, from where. This equation is called the thermal balance equation.

29. Application of the first law of thermodynamics to isoprocesses. Adiabat process. Irreversibility of thermal processes.

One of the main processes of work in most machines is the process of expanding gas with the performance of work. If with the isobar gas expansion from the volume V 1.to volume V 2. Moving the piston of the cylinder was l., then work A. Perfect gas is equal, or . If you compare the area under the isobar and isotherm, we can conclude that with the same expansion of the gas with the same initial pressure in the case of an isothermal process there will be less than the amount of work. In addition to the isobaric, isochlorine and isothermal processes there is so-called. Adiabat process. Adiabatar is called a process that occurs under the absence of heat exchange. Close to adiabatum can be considered a process of rapid expansion or gas compression. In this process, the work is performed due to changes in internal energy, i.e. Therefore, with an adiabatic process, the temperature decreases. Since, with an adiabatic gas compression, the gas temperature rises, the gas pressure with a decrease in volume increases faster than with an isothermal process.

The heat transfer processes are spontaneously implemented in only one direction. Always heat transmission occurs to a colder body. The second law of thermodynamics states that the thermodynamic process is not effective, as a result of which heat transfer from one body to another, more hot, without any other changes. This is scoring the creation of a second-sort eternal engine.

30. The principle of action of thermal motors. The efficiency of the thermal engine.

Usually in thermal machines, work is performed by expanding gas. Gas, making work when expanding, is called a working fluid. The expansion of the gas occurs as a result of increasing its temperature and pressure when heated. The device from which the working fluid gets the amount of heat Q. called heater. A device to which the machine gives the heat after performing the working stroke is called a refrigerator. First, the pressure is amoothorically growing, is isoicically expanding, is amootherally cooled, it is being squeezed.<рисунок с подъемником>. As a result of the operation of the working cycle, the gas returns to the initial state, its internal energy takes place of its initial value. It means that . According to the first law of thermodynamics ,. The work performed by the body per cycle is equal to Q. The amount of heat obtained by the body per cycle is equal to the difference from the heater and the given refrigerator. Hence, . The efficiency of the machine is called the relationship useful to energy used .

31. Evaporation and condensation. Saturated and unsaturated pairs. Air humidity.

The uneven distribution of the kinetic energy of thermal motion leads to that. That at any temperature, the kinetic energy of some part of the molecules may exceed the potential binding energy with the rest. The evaporation is called the process at which molecules are flying from the surface of the liquid or solid body. Evaporation is accompanied by cooling, because Faster molecules leave the liquid. The evaporation of the fluid in a closed vessel at a constant temperature leads to an increase in the concentration of molecules in a gaseous state. After a while there is a balance between the amount of evaporating molecules and returning to the liquid. A gaseous substance in dynamic equilibrium with its liquid is called a saturated ferry. Couples, located at a pressure below the pressure of a saturated pair, is called unsaturated. The pressure of the saturated pair does not depend at a constant temperature from the volume (from). With a constant concentration of molecules, the saturated steam pressure increases faster than the pressure of the ideal gas, because Under the action of temperature, the number of molecules increases. The ratio of the pressure of the water vapor at a given temperature to the pressure of the saturated pair at the same temperature, expressed as a percentage, is called relative humidity. The lower the temperature, the less the pressure of the saturated steam, thus, when cooled to a certain temperature, steam becomes saturated. This temperature is called dew point. t P..

32. Crystal and amorphous bodies. Mechanical properties of solid bodies. Elastic deformations.

Amorphous are called bodies, the physical properties of which are the same in all directions (isotropic bodies). The isotropy of physical properties is explained by the chaotic content of the molecules. Solid bodies in which molecules are ordered are called crystals. The physical properties of crystalline bodies of unequal in various directions (anisotropic bodies). The anisotropy of the properties of crystals is explained by the fact that with an ordered structure of the interaction force of unequal in various directions. The external mechanical effect on the body causes the displacement of atoms from the equilibrium position, which leads to a change in the shape and volume of the body - deformation. The deformation can be characterized by an absolute elongation equal to the difference in lengths before and after deformation, or relative elongation. When deforming the body arise for elasticity. The physical value equal to the ratio of the module of the force of elasticity to the area of \u200b\u200bthe body cross section is called mechanical voltage. With low deformations, the voltage is directly proportional to the relative elongation. Proportionality coefficient E. The equation is called the elastic modulus (Jung module). The elastic module is constant for this material. From where. The potential energy of the deformed body is equal to the work spent on stretching or compression. From here .

The law of the throat is performed only with small deformations. The maximum voltage at which it is still performed is called the proportionality limit. Behind this limit, the tension ceases to grow proportionally. Until some level, the stress is a deformed body will restore its sizes after removing the load. This point is called the limit of body elasticity. When the limit of elasticity is exceeded, plastic deformation begins, in which the body does not restore its former shape. In the area of \u200b\u200bplastic deformation, the voltage is almost no increase. This phenomenon is called material fluidity. For the yield strength, the voltage increases to the point called the strength of the strength, after which the voltage decreases up to the destruction of the body.

33. The properties of liquids. Surface tension. Capillary phenomena.

The possibility of free movement of molecules in the liquid causes fluid flow. The body in the liquid state does not have a constant shape. The fluid shape is determined by the form of the vessel and the forces of the surface tension. Inside the fluid, the force of attraction of molecules is compensated, and the surface is not. Any molecule at the surface is attracted by molecules inside the liquid. Under the action of these forces of the molecule to the surface are drawn inside until the free surface becomes minimal of all possible. Because The minimum surface with this volume has a ball, with a small action of other forces, the surface takes the shape of a spherical segment. The surface of the fluid at the edge of the vessel is called a meniscus. The wetting phenomenon is characterized by a boundary angle between the surface and the meniscus at the intersection point. The magnitude of the surface tension for the length D l. equal. The curvature of the surface creates an excessive pressure on the liquid equal to the famous corner and radius . The coefficient S is called the surface tension coefficient. The capillary is called a tube with a small inner diameter. With full wetting, the strength of the surface tension is directed along the body surface. In this case, the lifting of fluid on the capillary continues under the action of this force until the strength of gravity does not equilibrate the strength of the surface tension, since then.

34. Electric charge. The interaction of charged bodies. The law of the coulon. The law of conservation of an electric charge.

Neither the mechanic nor the ICT is able to explain the nature of the forces binding atoms. The laws of interaction of atoms and molecules can be explained on the basis of the idea of \u200b\u200belectrical charges.<Опыт с натиранием ручки и притяжением бумажки> The interaction of bodies detected in this experiment is called electromagnetic, and is caused by electrical charges. The ability of charges to attract and repelly explains the assumption about the existence of two types of charges - positive and negative. The bodies charged with the same charge are repelled, different things are attracted. The charge unit is a pendant - a charge passing through a cross-section of the conductor in 1 second at a current of 1 amp. In a closed system, into which electrical charges are not included and from which electrical charges do not exit under any interactions the algebraic amount of charges of all bodies constant. The main law of electrostatics, he is the law of Coulomb, it says that the interaction force module between two charges is directly proportional to the product of charge modules and inversely proportional to the square of the distance between them. The force is directed along the straight line connecting the charged bodies. Is the power of repulsion or attraction, depending on the sign of charges. Constant k. In the expression of the Culon law is equal . Instead, the coefficient is used by the so-called. Electric constant associated with the coefficient k. expression, from where. The interaction of motionless electrical charges is called electrostatic.

35. Electrical field. Electric field strength. The principle of superposition of electric fields.

There is an electric field around each charge on the basis of the theory of closestream. The electric field is a material object, constantly exists in space and can act on other charges. The electric field is distributed in space at the speed of light. The physical value equal to the ratio of the strength with which the electric field acts on a test charge (a point positive small charge that does not affect the field configuration), to the value of this charge, is called the electric field strength. Using the law of Coulomb possible, it is possible to obtain a formula for the field strength created by the charge. q. on distance r. from charge . The field strength does not depend on the charge to which it acts. If at a charge q. The electrical fields of several charges are operating simultaneously, the resulting force turns out to be equal to the geometric sum of the forces acting from each field separately. This is called the principle of superposition of electric fields. The line of electric field strength is called a tangent to which at each point coincides with the tension vector. Tension lines begin on positive charges and ends on negative, or go into infinity. The electric field whose tension is the same for everyone at any point of space, is called a homogeneous electric field. Approximately homogeneous can be considered the field between two parallel variepelly charged metal plates. With uniform charge distribution q. On the surface of the square S. Surface charge density is equal. For an infinite plane with surface charge density S field strength is the same in all points of space and equal .

36. The operation of the electrostatic field when charging the charge. Potential difference.

When the charge is moved by an electric field at a distance perfect work is equal . As in the case of the work of gravity, the work of the Coulomb force does not depend on the trajectory of the charge. When the direction of the movement vector is changed to 180 0, the operation of the field forces changes the sign to the opposite. Thus, the work of the power of the electrostatic field when the charge is moving along the closed contour is zero. The field, the operation of the forces of which along the closed trajectory is zero, is called a potential field.

Just like the body mass m. In the field of gravity, has potentially energy, proportional mass of the body, the electrical charge in the electrostatic field has potential energy W P.proportional to charging. The work of the power of the electrostatic field is equal to the change in the potential energy of charge taken with the opposite sign. At one point of the electrostatic field, different charges may have different potential energy. But the ratio of potential energy to the charge for this point is the value constant. This physical value is called the electric field potential, from where the potential charge energy is equal to the production of the potential at this point for the charge. The potential is a scalar value, the potential of several fields is equal to the sum of the potentials of these fields. The measure of energy change in the interaction of bodies is the work. When charging the charge, the operation of the power of the electrostatic field is equal to the change in energy with the opposite sign, therefore. Because Work depends on the difference in potentials and does not depend on the trajectory between them, the difference of potentials can be considered the energy characteristics of the electrostatic field. If the potential is at an infinite distance from charge to take equal to zero, then at a distance r. From charge it is determined by the formula .

The ratio of the work performed by any electric field when moving a positive charge from one point of the field to another, to the charge value is called voltage between these points, where does the work come from. In the electrostatic field, the voltage between the two any points is equal to the potential difference between these points. The unit of voltage (and the difference of potentials) is called volt ,. 1 volt is equal to such a tension in which the field makes a job in 1 joule to move charge in 1 pendant. On the one hand, the work on the movement of the charge is equal to the work of force to move. On the other hand, it can be found on the well-known voltage between the paths of the path. From here. The unit of electric field strength is a volt on the meter ( v / M.).

Condenser is a system of two conductors separated by a dielectric layer, the thickness of which is small compared to the size of the conductors. Between the plates, the field strength is equal to the double tension of each of the plates, outside the plates it is zero. The physical value equal to the ratio of the charge of one of the plates to the voltage between the plates is called the electrical capacity of the condenser. The unit of electrical capacity - Farad, with a capacity of 1 pharade, has a capacitor, between the plates of which the voltage is 1 volt when the charge of the charge on 1 pendant. The field strength between the solid capacitor plates is equal to the sum of the tension of the plates to it. , and that for a homogeneous field is performed, then . The electrical capacity is directly proportional to the area of \u200b\u200bthe plates and is inversely proportional to the distance between them. When administered between the dielectric plates, its electrical capacity increases in e times, where E is the dielectric constant of the material being introduced.

38. The dielectric constant. Electric field energy.

The dielectric constant is a physical value that characterizes the ratio of the electric field strength module in a vacuum to the electrical field module in a homogeneous dielectric. The operation of the electric field is equal, but when charging the capacitor, its voltage grows from 0 before U., so . Consequently, the potential energy of the capacitor is equal to.

39. Electric current. Current power. Conditions of the existence of an electric current.

Electric current is called an ordered movement of electrical charges. For the direction of current, the movement of positive charges is taken. Electrical charges can orderly move under the action of the electric field. Therefore, a sufficient condition for the existence of current is the presence of a field and free charge carriers. The electric field can be created by two connected varianetically charged bodies. Ratio of charge D. q.carrying through the cross section of the conductor over the time interval d t. To this interval is called current. If the current current does not change over time, the current is called constant. So that the current existed the conductor for a long time, it is necessary that the conditions that cause the current are unchanged.<схема с один резистором и батареей>. Forces causing the charge of charge within the current source are called third-party forces. In galvanic element (and any battery - G. ???) They are the forces of the chemical reaction, in the DC car - the power of Lorentz.

40. Ohma law for chain section. Resistance to conductors. The dependence of the resistance of conductors from temperature. Superconductivity. Sequential and parallel connection of the conductors.

The ratio of the voltage between the ends of the plot of the electrical circuit to the strength of the current is the value of the constant, and is called resistance. The resistance unit 0 Ohm, resistance in 1 ohms has such a plot of a chain, in which 1 ampere voltage is 1 volt. Resistance is directly proportional to the length and inversely proportional to the cross-sectional area, where R is a specific electrical resistance, the value is constant for this substance under these conditions. When heated, the resistivity of the metals is increased by linear law, where R 0 is a resistivity at 0 ° C, A is the temperature coefficient of resistance, special for each metal. With close to absolute zero temperatures, the resistance of substances drops sharply to zero. This phenomenon is called superconductivity. The passage of current in superconducting materials occurs without lost heating of the conductor.

Ohm's law for the chain section is called the equation. With a consistent connection of the conductors, the current is the same in all conductors, and the voltage at the ends of the chain is equal to the amount of voltages on all successively enabled conductors. . With a consistent connection of the conductors, the overall resistance is equal to the amount of resistance components. With a parallel connection, the voltage at the ends of each section of the chain is equally, and the current force branches into separate parts. From here. With parallel conducting conductors, the value inverse the total resistance is equal to the sum of the reverse resistances of all parallel conductor on.

41. Work and current power. Electromotive force. Ohm law for full chain.

The work of the power of the electric field creating an electric current is called the current operation. Work BUT current on the plot with resistance R. During D. t. equal. The power of the electric current is equal to the ratio of the time of the commission, i.e. . Work is expressed as usual, in joules, power - in watts. If there is no work on the circuit area under the action of the electric field and chemical reactions do not occur, then the work leads to the heating of the conductor. At the same time, the work is equal to the number of heat released by the conductor with the current (the law of Joule-Lenza).

In the electrical circuit, the work is performed not only in the outside site, but also in the battery. The electrical resistance of the current source is called internal resistance r.. In the inner segment of the chain, the amount of heat equal is allocated. The full operation of the power of the electrostatic field when moving along a closed contour is zero, so all the work is performed due to external forces supporting constant voltage. The relationship of the external forces to the portable charge is called the electromotive source force, where D q. - Portable charge. If, as a result of the passage of the DC, only the heating of the conductors occurred, then by the law of energy conservation . . The yaux in the electrical circuit is directly proportional to the EMF and inversely proportional to the complete chain resistance.

42. Semiconductors. Electrical conductivity of semiconductors and its dependence on temperature. Own and impurity conductivity of semiconductors.

Many substances do not spend current as well as metals, but at the same time are not dielectrics. One of the differences between semiconductors is that when heated or illumination, their specific resistance does not increase, but decreases. But the main practically applicable property turned out to be one-sided conductivity. Due to the uneven distribution of thermal motion energy in a semiconductor crystal, some atoms are ionized. Released electrons cannot be captured by surrounding atoms, because Their valence is saturated. These free electrons can move in a metal, creating an electronic conductivity current. At the same time, an atom, an electron was broken from the shell, becomes an ion. This ion is neutralized by capturing the neighbor's atom. As a result of such a chaotic movement, there is a movement of the place with the missing ion, which is externally visible as moving a positive charge. This is called hole conduction current. In the perfect semiconductor crystal, the current is created by moving an equal amount of free electrons and holes. This type of conductivity is called its own conductivity. When the temperature decreases, the number of free electrons, proportional to the average energy of atoms, falls and the semiconductor becomes similar to the dielectric. In the semiconductor to improve the conductivity, impurities are sometimes added, which are donor (increase the number of electrons without increasing the number of holes) and acceptor (increase the number of holes without increasing the number of electrons). Semiconductors, where the number of electrons exceeds the number of holes, is called electronic semiconductors, or N-type semiconductors. Semiconductors, where the number of holes exceeds the amount of electrons, is called hole semiconductors, or P-type semiconductors.

43. Semiconductor diode. Transistor.

Semiconductor diode consists of p-N. Transition, i.e. Of the two connected semiconductors of various types of conductivity. When connected, electrons diffusion occurs in r-semiconductor. This leads to the appearance of uncompensated positive ions of the donor impurity in the electronic semiconductor, and in the holes - negative ions of acceptor impurities that captured the prediffered electrons. A electric field arises between the two layers. If there is a positive charge on an electronic conductivity area, and the area with a hole is negative, then the locking field will increase, the current will decrease sharply and almost independent of the voltage. This method of inclusion is called locking, and the current current in the diode is reverse. If there is a positive charge on the area with a hole conduction, and the area with the electronic is negative, then the locking field will weaken, the current strength through the diode in this case depends only on the resistance of the outer chain. This method of inclusion is called bandwidth, and the current current in the diode is direct.

Transistor, it is semiconductor triode, consists of two p-N. (or n-P.) Transitions. The middle part of the crystal is called base, extreme - emitter and collector. Transistors in which the base has hole conductivity is called transistors p-N-P Transition. To actuate the transistor p-N-P-Type to the collector is solaring the tension of the negative polarity relative to the emitter. The database voltage can be both positive and negative. Because holes larger, then the main current through the transition will be a diffusion stream of holes from r- Registration. If you have a small direct voltage on the emitter, then the holes diffuse from it will flow r- Registry B. N.- Regard (database). But because The base is narrow, then the holes fly through it, accelerating the field, in the collector. (???, Something I missed ...). The transistor is able to distribute the current, thereby enhanced it. The ratio of the current change in the collector's circuit to the change of current in the base chain, with other things being equal, the value is a constant, called the integral coefficient of the base current transmission. Consequently, changing the current in the circuit of the base, it is possible to obtain changes in the current circuit current. (???)

44. Electric current in gases. Types of gas discharges and their application. The concept of plasma.

Gas under the influence of light or heat can become a current conductor. The phenomenon of passing current through the gas under the condition of external influence is called an independent electrical discharge. The process of gas ions under the influence of temperature is called thermal ionization. The occurrence of ions under the influence of light radiation - photoionization. Gas, in which a significant part of molecules is ionized, is called plasma. Plasma temperature reaches several thousand degrees. Electrons and plasma ions are capable of moving under the influence of the electric field. With an increase in the intensity of the field, depending on the pressure and nature of the gas, it occurs a discharge without the impact of external ionizers. This phenomenon is called an independent electrical discharge. In order for the electron when hitting the atom, it is necessary, it is necessary that he possessed the energy of no less ionization. This electron electron can be purchased under the influence of the forces of the external electric field in the gas on the path of free run, i.e. . Because The length of the free mileage is small, independent discharge is possible only with high field strength. At low gas pressure, the gasey discharge is formed, which is explained by increasing the conductivity of the gas at a permit (the path of the free mileage increases). If the current current in an independent discharge is very high, the electrons can cause heating the cathode and anode. From the surface of the cathode at high temperatures, electron emission occurs that supports the discharge in the gas. This type of discharge is called arc.

45. Electric current in vacuum. Thermoelectronic emission. Cathode-ray tube.

There are no carriers of free charge in vacuo, so there is no external influence of the current in vacuo. It may occur if one of the electrodes heat up to a high temperature. The heated cathode emits electrons from its surface. The phenomenon of emission of free electrons from the surface of heated bodies is called thermoelectronic emissions. The simplest instrument using thermoelectronic emissions is an electrovacable diode. Anode consists of a metal plate, a cathode - from a thin rolled wire spiral. Around the cathode, an electronic cloud is created when it is heated. If you connect the cathode to the positive imaging of the battery, and the anode to the negative, the field inside the diode will shift the electrons to the cathode, and there will be no current. If you connect on the contrary - the anode to the plus, and the cathode to minus is the electrical field to move the electrons towards the anode. This explains the property of one-sided conductivity of the diode. The electrons moving from the cathode to the anode can be controlled using an electromagnetic field. For this, the diode is modified, and a grid is added between the anode and cathode. The resulting device is called trigger. If the grid suggests a negative potential, the field between the grid and the cathode will prevent the electron movement. If you submit a positive - then the field will prevent the movement of electrons. The electrons emitted by the cathode can be spoken by electric fields to overclock up to high speeds. The ability of electron beams to deviate under the action of electromagnetic fields is used in the ELT.

46. \u200b\u200bMagnetic interaction of currents. A magnetic field. The force acting on the conductor with the current in the magnetic field. Induction of the magnetic field.

If a current of one direction is passed through the conductors, they are attracted, and if equal, then repel. Consequently, there is some interaction between the conductors, which cannot be explained by the presence of an electric field, because In general, the conductors are electronic. The magnetic field is created by moving electrical charges and acts only on moving charges. The magnetic field is a special type of matter and continuously in space. The passage of electric current over the conductor is accompanied by the generation of the magnetic field regardless of the medium. Magnetic interaction of the conductors is used to determine the value of the current force. 1 amp is the current strength passing through two parallel conductors ¥ lengths, and a small cross section, located at a distance of 1 meter from each other, at which the magnetic flux causes at low power of the interaction equal to each meter of length. The force with which the magnetic field acts on the conductor with the current is called the force of the ampere. To characterize the ability of the magnetic field to effect on the conductor with a current there is a value called magnetic induction. The magnetic induction module is equal to the maximum value of the amp force acting on the conductor with the current, to the power of the current in the conductor and its length. The direction of the induction vector is determined by the rule of the left hand (by hand the conductor, in the thumb, in the palm - induction). The unit of magnetic induction is Tesla, equal to the induction of such a magnetic flux, in which the maximum strength of the ampere 1 Newton acts on 1 amp 1 meter. The line, at any point of which the vector of magnetic induction is directed by a tangent, is called a magnetic induction line. If in all points of some space, the induction vector has the same value by the module and the same direction, the field in this part is called uniform. Depending on the angle of inclination of the conductor with a current relative to the magnetic induction vector of the amper forces, it changes in proportion to the sinus of the angle.

47. Ampere Law. Magnetic field action on a moving charge. Lorentz power.

The effect of the magnetic field on the current in the conductor suggests that it acts on moving charges. Tok Power I. In the conductor associated with concentration n. free charged particles, speed v. their ordered movement and square S. cross section conductor expression where q. - charge of one particle. Substituting this expression in the formula of the amper power, we get . Because nSL. equal to the number of free particles in the conductor length l., then the force acting on the side of the field per charged particle moving at speeds v. At an angle A to the magnetic induction vector B. equal . This force is called Lorentz's force. The direction of the Lorentz force for a positive charge is determined by the rule of the left hand. In a homogeneous magnetic field, a particle, moving perpendicular to the lines of the magnetic field induction, under the action of the force of Lorentz acquires centripetric acceleration and moves around the circumference. Radius of the circle and the period of circulation are determined by expressions . The independence of the period of reforming of radius and speed is used in the accelerator of charged particles - cyclotron.

48. Magnetic properties of the substance. Ferromagnetics.

Electromagnetic interaction depends on the medium in which the charges are located. If you have a small coil with a small coil, then it will dismay. If insert the iron core into a large insert, then the deviation will increase. This change shows that induction varies when the core is making. Substances significantly reinforcing the external magnetic field are called ferromagnets. The physical value showing how many times the inductance of the magnetic field in the medium differs from the inductance of the field in vacuo, is called magnetic permeability. Not all substances enhance the magnetic field. Paramagnetics create a weak field that coincides in the direction with external. Diamagnets weakening your field an external field. Ferromagnetism is explained by the magnetic properties of the electron. The electron is a moving charge, and therefore has its own magnetic field. In some crystals, there are conditions for evil parallel orientation of electron magnetic fields. As a result, inside the ferromagnet crystal, magnetized areas occur, called domains. With an increase in the external magnetic field of the domains, they organize their orientation. With a certain induction value, there is a complete streamlining of the orientation of domains and comes magnetic saturation. When the ferromagnet is derived from an external magnetic field, not all domains lose their orientation, and the body becomes a permanent magnet. The ordering of the orientation of domains can be impaired by thermal fluctuations of atoms. The temperature in which the substance ceases to beferromagnetically is called the Curie temperature.

49. Electromagnetic induction. Magnetic stream. The law of electromagnetic induction. Lenza rule.

In a closed circuit, an electric current occurs when changing the magnetic field. This current is called induction current. The phenomenon of current occurrence in a closed circuit with changes in the magnetic field, permeating the contour, is called electromagnetic induction. The appearance of the current in the closed circuit indicates the presence of third-party forces of non-electrostatic nature or the occurrence of EDC induction. A quantitative description of the phenomenon of electromagnetic induction is based on the establishment of an EDC induction and a magnetic flow. Magnetic flow F. Through the surface is a physical value equal to the piece of surface area S.on magnetic induction vector module B. And on the cosine of the angle A between it and the normal to the surface. The unit of magnetic flux - Weber, equal to the flow, which, with uniform descending to zero, causes 1 volt to zero in 1 second. The direction of the induction current depends on whether the flow is increasing or decreases, permeating the contour, as well as on the direction of the field relative to the contour. Lenz's general formulation: The induction current appears in the closed circuit has such a direction that the magnetic flux created by it through the area bounded by the contour, seeks to compensate for the change in the magnetic flux, which is called this current. The law of electromagnetic induction: EMF induction in a closed loop is directly proportional to the rate of change of magnetic flux through the surface bounded by this circuit and is equal to the rate of change of this stream, and taking into account the Lenz rule. When changing the EMF in the coil consisting of n. identical turns, common EMF in n. Once more EDC in one separate twist. For a homogeneous magnetic field based on the determination of the magnetic flux, it follows that induction is 1 Tesla, if the flow through the circuit in 1 square meter is 1 Weber. The occurrence of electric current in a fixed conductor is not explained by magnetic interaction, because The magnetic field is valid only on moving charges. The electric field arising from the change in the magnetic field is called a vortex electric field. The work of the forces of the vortex field to move charges and is EMF induction. The vortex field is not associated with charges and is closed lines. The work of this field for a closed loop can be different from zero. The phenomenon of electromagnetic induction also occurs at a reprehensive source of the magnetic flux by a jogging conductor. In this case, the cause of EMF induction equal to is the power of Lorentz.

50. The phenomenon of self-induction. Inductance. Magnetic field energy.

Electric current passing through the conductor creates a magnetic field around it. Magnetic flow F. Through the contour proportional to the magnetic induction vector IN, and induction, in turn, current power in the conductor. Consequently, it can be written for magnetic flux. The proportionality coefficient is called inductance and depends on the properties of the conductor, its size and the environment in which it is located. Inductance unit - Henry, inductance is 1 Henry, if at a current of 1 amp magnetic flow is 1 Weber. When changing the current strength in the coil, a magnetic flux created by this current is changed. The change in the magnetic flux causes an occurrence in the EMF induction coil. The phenomenon of the occurrence of EMF induction in the coil as a result of the change in the current in this chain is called self-induction. In accordance with the Rules of Lenz, self-induction is preventing increasing when turning on and descending when the chain is turned off. EMF of self-induction arising in an inductance coil L., according to the law of electromagnetic induction is equal to . Let if the network is disconnected from the source, the current decreases according to the linear law. Then EMF self-induction has a constant value equal to . During t. With linear descending, the chain will pass. At the same time, the operation of the electric current is equal . This work is performed by the light of energy W M. Magnetic field coil.

51. Harmonic oscillations. Amplitude, period, frequency and phase of oscillations.

Mechanical oscillations refer to the movements of bodies, repeating exactly or approximately equally at the same time intervals. The forces acting between bodies within the system under consideration are called internal forces. Forces acting on the bodies of the system from other bodies, are called external forces. Free oscillations are oscillations that have arisen under the influence of domestic forces, for example, a pendulum on a thread. Wipes under the actions of external forces - forced oscillations, for example, a piston in the engine. The general features of all types of oscillations are the repeatability of the movement process at a certain time interval. Harmonic is called oscillations described by the equation . In particular, fluctuations arising in a system with one returning force proportional to deformation are harmonic. The minimum interval through which the repetition of the body moves is called the oscillation period T.. Physical value, reverse period of oscillations and characterizing the number of oscillations per unit of time is called frequency. Frequency is measured in hertz, 1 Hz \u003d 1 s -1. The concept of cyclic frequency is also used, which determines the number of oscillations for 2p seconds. The maximum displacement module from the equilibrium position is called amplitude. The value under the sign of Kosinus is the oscillation phase, J 0 - the initial phase of oscillations. Derivatives are also harmoniously changed, and, and complete mechanical energy at random deviation h.(angle, coordinate, etc.) is equal where BUT and IN - Constants defined by the parameters of the system. Differentizing this expression and taking into account the lack of external forces, it can be written that, from where.

52. Mathematical pendulum. Cargo oscillations on the spring. The period of oscillations of the mathematical pendulum and cargo on the spring.

The body of small sizes, suspended on the unseasonable thread, the mass of which is negligible compared to the mass of the body, is called a mathematical pendulum. The vertical position is the position of equilibrium, in which the force of gravity is equalized by the force of elasticity. With small deviations of the pendulum on the equilibrium position, an equal force arises, aimed at the position of equilibrium, and its oscillations are harmonic. The period of harmonic oscillations of a mathematical pendulum with a small corner of the scope is equal. To bring this formula to write Newton's second law for the pendulum. The light of gravity and the force of tensioning the thread act on the pendulum. Their self-absorbing deviation at a small angle is equal. Hence, From! .

With harmonic fluctuations in the body suspended on the spring, the strength of elasticity is equal to the law of the throat. According to the second law of Newton.

53. Transformation of energy in harmonic oscillations. Forced oscillations. Resonance.

With the deviation of the mathematical pendulum from the equilibrium position, its potential energy increases, because Increases the distance to the Earth. When moving to the position of equilibrium, the speed of the pendulum increases, and the kinetic energy increases, by reducing the stock potential. In the equilibrium position kinetic energy - the maximum, potential is minimal. In the position of the maximum deviation - on the contrary. Spring is the same, but there is no potential energy in the field of land, but the potential energy of the spring is taken. Free oscillations are always attenuating, i.e. with a decreasing amplitude, because Energy is spent on interaction with surrounding bodies. Energy losses are equal to the work of external forces during the same time. The amplitude depends on the frequency of change change. It reaches the maximum amplitude at a frequency of oscillations of the external force that coincides with its own frequency of system oscillations. The phenomenon of increasing the amplitude of the forced oscillations under the described conditions is called resonance. Since with resonance, the external force makes the maximum positive work for the period, then the resonance condition can be defined as the condition of maximum energy transmission system.

54. Distribution of oscillations in elastic media. Transverse and longitudinal waves. Wavelength. The connection of the wavelength at the speed of its distribution. Sound waves. Sound speed. Ultrasound

The excitation of oscillations in one place of the medium causes forced oscillations of neighboring particles. The distribution process of oscillations in space is called wave. Waves in which oscillations occur perpendicular to the direction of propagation are called transverse waves. Waves in which oscillations occur along the direction of the wave propagation are called longitudinal waves. Longitudinal waves may occur in all media, transverse - in solid bodies under the action of elasticity for the deformation or forces of surface tension and gravity forces. The speed of propagation of oscillations V in space is called the wave speed. Distance L between points closest to each other, fluctuating in the same phases, is called a wavelength. The dependence of the wavelength from the speed and the period is expressed as, or. If the waves occur, their frequency is determined by the frequency of the source oscillations, and the speed - the medium where they spread, therefore the waves of one frequency may have different lengths in different environments. Compression and airproof processes are distributed in all directions and are called sound waves. Sound waves are longitudinal. The speed of the sound depends, as well as the speed of any waves, from the medium. In the air, the speed of sound 331 m / s, in water - 1500 m / s, in steel - 6000 m / s. Sound pressure - additionally pressure in gas or fluid caused by sound wave. The intensity of the sound is measured by the energy carried by the sound waves per unit of time through the unit of cross-sectional area, perpendicular to the direction of propagation of the waves, and is measured in watts per square meter. The intensity of the sound determines its volume. Sound height is determined by the frequency of oscillations. Ultrasound and infrasound call sound oscillations lying outside the hearing frequencies 20 kilohertz and 20 hertz, respectively.

55.Found electromagnetic oscillations in the circuit. Transformation of energy in the oscillatory circuit. Own frequency of oscillations in the circuit.

The electrical oscillatory contour is called a system consisting of a condenser and coil connected to a closed chain. When connecting the coil to the condenser in the coil, the current occurs and the energy of the electric field turns into the magnetic field energy. The capacitor is not discharged instantly, because This is hampered by EMF self-induction in the coil. When the capacitor is completely discharged, the EMF of self-induction will prevent decreasing current, and the magnetic field energy will switch to the energy of the electric. The current arising from this, charges the condenser, and the charge sign on the plated will be the opposite of the original. After that, the process is repeated until all the energy is spent on the heating of the chain elements. Thus, the magnetic energy of the oscillatory circuit turns into the energy of electrical and back. For the total energy of the system it is possible to record relationships: Where to arbitrary time . As you know, for a complete chain . Believing that in the ideal case R »0., I finally get, or. The solution of this differential equation is a function where. The value w is called its own circular (cyclic) frequency of oscillations in the circuit.

56. Forced electrical oscillations. Variable electric current. Alternator. Power AC.

The alternating current in the electrical circuits is the result of the excitation of forced electromagnetic oscillations. Let the flat rounda have an area S. and vector induction B. It is with a perpendicular to the plane of the turn angle j. Magnetic flow F. Through the area of \u200b\u200bthe turn in this case is determined by the expression. When rotating the turn with a frequency n, the angle of J is changing according to the law., Then the expression for the flow will take the form. Magnetic Flow Changes Create Induction EMPS equal to minus flow change rate. Consequently, the change in EMF induction will be held by harmonious law. The voltage removed from the output of the generator is proportional to the number of turns of the winding. When changing the voltage of harmonic law The field strength in the conductor varies on the same law. Under the action of the field, the frequency and phase of which coincide with the frequency and phase of voltage oscillations are arising. The fluctuations in the current in the chains are forced to emerge under the influence of the applied alternating voltage. When the current and voltage phases coincides, the power of the alternating current is equal to or . The average value of the cosine square for the period is 0.5, therefore. The current value of the current value is called DC strength, emitting the same amount of heat in the conductor as alternating current. With amplitude I Max Harmonic fluctuations in current force acting voltage equals. The active voltage value is also less than its amplitude value. The average power of the current at the coincidence of the oscillation phases is determined through the active voltage and current strength.

5 7. Active, inductive and capacitive resistance.

Active resistance R. It is called a physical value equal to the ratio of power to the square of the current force, which is obtained from the expression for power. At small frequencies, it practically does not depend on the frequency and coincides with the electrical resistance of the conductor.

Suppose that the coil is turned on in the alternating current circuit. Then, when the current change under the law in the coil, EMF of selfinducia occurs. Because The electrical resistance of the coil is zero, then the EMF is equal to minus the voltage at the ends of the coil created by the external generator (??? What else is the generator ???). Consequently, the change in current causes a change in voltage, but with a phase shift . The product is an amplitude of oscillations voltage, i.e. . The ratio of the amplitude of voltage fluctuations on the coil to the amplitude of the current oscillations is called inductive resistance .

Let the condenser be in the chain. With its inclusion, it charges a quarter of the period, then heels as much as the same, but with a change of polarity. When the voltage is changed on the harmonic law condenser The charge on its plates is equal. Current in the chain occurs when the charge changes:, similarly, the case with the coil of the amplitude of the current force fluctuations is equal to . The value equal to the ratio of amplitude to the strength of the current is called capacitive resistance .

58. Ohm law for alternating current.

Consider a chain consisting of successively connected resistors, coils and capacitor. At any time, the applied voltage is equal to the amount of voltages on each element. Current fluctuations in all elements occur by law. The voltage fluctuations on the resistor coincide on the phase with the fluctuations of the current strength, the voltage fluctuations on the condenser are lagging behind the phase from the fluctuations of the current, the voltage fluctuations on the coil is ahead of the current fluctuation phase (why are there behind something ???). Therefore, the condition of equality of the voltage amount can be generally written as. Taking advantage of the vector diagram, you can see that the voltage amplitude in the chain is equal, or i.e. . Full chain resistance denote . It is obvious from the diagram that the voltage also fluctuates the harmonic law. . The initial phase j can be found by the formula . Instant power in the variable current circuit is equal. Since the average cosine square value for the period is 0.5 ,. If there is a coil and condenser in the chain, then according to the law of Ohm for AC. The value is called power coefficient.

59. Resonance in the electrical circuit.

Capacitive and inductive resistance depend on the frequency of the applied voltage. Therefore, with a constant amplitude of the voltage of the amplitude of the current force depends on the frequency. With this frequency value at which, the sum of the voltage on the coil and the condenser becomes zero, because Their oscillations are opposite to phase. As a result, the voltage on the active resistance in the resonance is equal to the full voltage, and the current power reaches the maximum value. Express inductive and capacitive resistance at resonance: , hence . This expression shows that with the resonance of the amplitude of voltage fluctuations on the coil and the condenser can exceed the amplitude of the oscillations of the applied voltage.

60. Transformer.

The transformer is two coils with different number of turns. When applied to one of the coils of voltage in it occurs. If the voltage changes the harmonic law, then the same law will change the current. Magnetic stream passing through the coil is equal to . When changing the magnetic flux in each turn of the first coil, the self-induction EMD appears. The work is an amplitude of EDC in one turn, the same EDC in the primary coil. The secondary coil permeates the same magnetic flow, so. Because Magnetic streams are the same, then. Active winding resistance is not enough compared to inductive resistance, so the voltage is approximately equal to EDC. From here. Coefficient TO called a transformation coefficient. Losses on the heating of wires and cores are small, so F. 1 "F 2. The magnetic flow is proportional to the strength of the current in the winding and the number of turns. From here, i.e. . Those. The transformer increases the voltage in TO Once, reducing current current into the same time. Current power in both chains when disregarding losses is the same.

61. Electromagnetic waves. The speed of their distribution. Properties of electromagnetic waves.

Any change in the magnetic flux in the circuit causes the induction current in it. Its appearance is explained by the emergence of a vortex electric field with any change in the magnetic field. The vortex electric poda has the same property as an ordinary one to generate a magnetic field. Thus, one day the process of mutual generation of magnetic and electric fields continuously continues. Electric and magnetic fields that make up electromagnetic waves may exist in vacuo, unlike other wave processes. From experiments with interference, the rate of propagation of electromagnetic waves was established, which was approximately. In general, the speed of the electromagnetic wave in an arbitrary environment is calculated by the formula. The energy density of the electrical and magnetic component is equal to each other: From where. The properties of electromagnetic waves are similar to the properties of other wave processes. When the boundaries of the section of two environments are partially reflected, partially refracted. From the surface of the dielectric do not reflect, from metals are not fully reflected. Electromagnetic waves have interference properties (hertz experience), diffraction (aluminum plate), polarization (grid).

62. Radiocommunication principles. The simplest radio receiver.

To carry out radio communications, it is necessary to ensure the possibility of radiation of electromagnetic waves. The greater the angle between the capacitor plates - the more freely the EM wave is distributed in space. In fact, the open circuit consists of a coil and a long wire - antennas. One end of the antenna is grounded, the other is raised above the ground. Because The energy of electromagnetic waves is proportional to the fourth degree, then with the oscillations of the alternating current of the sound frequencies of the EM wave almost do not occur. Therefore, the principle of modulation is frequency, amplitude or phase. The simplest modulated oscillation generator is shown in the figure. Let the frequencies of the circuit vary by law. Let the frequency of modulated sound oscillations also change as And W.<(What is the damn exactly ???) (G - value, reverse resistance). Substituting into this expression of voltages, where, we get. Because with frequency resonance, far from the frequency of the resonance, are cut, then from the expression for i. The second, third and fifth components disappear, i.e. .

Consider the simplest radio. It consists of an antenna, an oscillatory circuit with a capacitor of a variable capacity, a detector diode, a resistor and a telephone. The frequency of the oscillating circuit is chosen in such a way that it coincides with the carrier frequency, while the oscillation amplitude on the condenser becomes the maximum. This allows you to select the desired frequency of all accepted. From the circuit, the modulated high frequency fluctuations come to the detector. After passing the detector, the current every halfer the capacitor charges, and the following semi-wheels, when the current does not pass through the diode, the capacitor is discharged through the resistor. (I understood correctly ???).

64. Analogy between mechanical and electrical oscillations.

The analogies between mechanical and electrical oscillations look like this:

Coordinate
Speed		Tok Power
Acceleration		Current change rate
		Inductance
Rigidity		The quantity, inverse electrical capacity
		Voltage
Viscosity		Resistance
Potential energy deformed spring		Electric field energy condenser
Kinetic energy, where. 65. Scale of electromagnetic emissions. The dependence of the properties of electromagnetic radiation from the frequency. The use of electromagnetic radiation. The range of electromagnetic ox length from 10 -6 m to m is radio waves. Used for television and radio communications. Length from 10 -6 m to 780 nm - infrared waves. Visible light - from 780 nm to 400 nm. Ultraviolet radiation - from 400 to 10 nm. Radiation in the range from 10 nm to 10 PM - X-ray radiation. Smaller wavelengths correspond to gamma radiation. (Application ???). The smaller the wavelength (consequently, above the frequency), the less the waves are absorbed by the medium. 65. Straight spread of light. The speed of light. Laws of reflection and refraction of light. Direct, indicating the direction of light propagation, is called a light beam. At the border of the two media, the light may be partially reflected and distributed in the first medium in a new direction, and also partially go through the border and spread in the second environment. The falling ray, reflected and perpendicular to the border of two environments, restored at the point of the fall, lying the same plane. The reflection angle is equal to the angle of fall. This law coincides with the law of reflection of waves of any nature and is proved by the Guigens principle. When the limit of the border of the section of two environments is passed, the sinus attitude of the angle of the fall to the sinus of the refractive angle is the value is permanent for two media data.<рисунок>. Value n. called refractive index. The refractive index of the medium relative to the vacuum is called an absolute refractive index of this medium. When observing the refractive effect, it can be seen that in the case of a transition of an environment of an optically more dense medium in less dense, with a gradual increase in the incidence of the fall, it is possible to achieve this value that the refractive angle will become equal. At the same time, equality is performed. The angle of falling A 0 is called the limiting angle of complete reflection. At angles, large a 0, there is a complete reflection. 66. Lens, image building. Lens formula. The lens is called a transparent body bounded by two spherical surfaces. The lens, which is thicker than in the middle, is called concave, which in the middle thicker is convex. Direct, passing through the centers of both spherical lens surfaces is called the main optical axis of the lens. If the thickness of the lens is small, then it can be said that the main optical axis intersects with a lens at one point, called the optical center of the lenses. Direct, passing through the optical center is called a side optical axis. If on the lens to send a beam of light parallel to the main optical axis, then the convex lens bundle will gather at the point F. In the lenses formula, the distance from the lenses to the imaginary image is considered negative. The optical power of the biconotype (and indeed any) the lens is determined from the radius of its curvature and the refractive index with glass and air . 66. Coherence. Interference of light and its use in the technique. Diffraction of light. Diffraction grating. In the phenomena of diffraction and interference, the wave properties of light are observed. Two light frequencies, the difference in the phases of which is zero, are called coherent to each other. In interference - the addition of coherent waves - there is a resistant interference pattern of maxima and luminous minima. With the difference in the course there is an interference maximum, with - Minimum. The phenomenon of the deviation of light from straight propagation during the passage of the region is called the diffraction of light. This phenomenon is explained by the Guygens-Fresnel principle: perturbation at any point is the result of the interference of secondary waves emitted by each element of the wave surface. Diffraction is used in spectral devices. An element of these devices is a diffraction grid, which is a transparent plate with a system of opaque parallel bands located at a distance d. Friend from each other. Let a monochromatic wave fall on the grille. As a result of diffraction from each slit, the light applies not only in the original direction, but also in all others. If you put a lens behind the bars, then in the focal plane parallel rays from all the cracks will be gather in one strip. Parallel rays go with the difference in the course. With the equality of the movement difference in an integer number of waves, the interference maximum of light is observed. For each wavelength, the maximum condition is performed at its value of the angle j, so the grill decomposes the white light into the spectrum. The larger the wave length, the greater the angle. 67. Dispersion of light. Spectrum of electromagnetic radiation. Spectroscopy. Spectral analysis. Sources of radiation and types of spectra. A narrow parallel beam of white light when passing through a prism decomposes on bundles of light of different color. The color strip apparently is called a solid spectrum. The phenomenon of the dependence of the speed of light from the wavelength (frequency) is called the light dispersion. This effect is explained by the fact that the white light consists of an em-waves of different wavelengths, from which the refractive index depends. It has the greatest value for the shortest wave - purple, the smallest - for red. In vacuum, the speed of light regardless of its frequency is the same. If the source of the spectrum is a rarefied gas, the spectrum has the kind of narrow lines on a black background. Compressed gases, liquids and solid bodies emit a solid spectrum, where the colors smoothly go into each other. The nature of the spectrum is explained by the fact that each element is inherent in its specific set of radiated spectrum. This property allows the use of spectral analysis to identify the chemical composition of the substance. The spectroscope is called the device by which the spectral composition of the light emitted by some source is investigated. The decomposition is performed using a diffraction lattice (better) or a prism, a quartz optics are applied to study the ultraviolet region. 68. Photo effect and its laws. Quanta light. Einstein equation for photo effect. Applying photo effect in the technique. The phenomenon of emanating electrons from solid and liquid bodies under the influence of light is called an external photoelectric effect, and the electrons-torn in this way - photoelectrons. Experienced the laws of the photo effect - the maximum speed of photoelectrons is determined by the frequency of light and does not depend on its intensity, for each substance there is its own red border of photo effect, i.e. Such a frequency N min, in which the photoelectron is still possible, the number of photoelectrons, pulled in a second, is directly proportional to the light intensity. It also establishes the randomity of the photo effect - it occurs instantly after the start of illumination, provided that the red border is exceeded. An explanation of the photo effect is possible with the help of a quantum theory that approves energy discreteness. The electromagnetic wave, on this theory, consists of separate portions - quanta (photons). When absorbing the energy quantum, the photoelectron acquires kinetic energy, which can be found from the Einstein equation for a photo effect , where and 0 is the operation of the output, the parameter of the substance. The number of photoelectrons leaving the surface of the metal is proportional to the amount of electrons, which, in turn, depends on the illumination (light intensity). 69. Rutterford's experiments on the dissipation of alpha particles. Nuclear atom model. Quantum postulates boron. The first model of the structure of the atom belongs to Thomson. He suggested that the atom is a positively charged ball, inside which are lined with inclusions of negatively charged electrons. Rutherford has carried out experience in the destruction of rapid alpha particles of the metal plate. In this case, it was observed that some of them are slightly deviated from straight-line propagation, and some proportion - on the corners of more than 2 0. This was explained by the fact that the positive charge in the atom is contained not evenly, but in some volume, significantly smaller size of the atom. This central part was called the atom core, where a positive charge is concentrated and almost all of the mass. The radius of the atomic nucleus has the size of about 10 -15 m. Also Rangeford suggested so-called. The planetary model of the atom in which electrons rotate around the atom as the planet around the sun. The radius of the farthest orbit \u003d atom radius. But this model contradicted electrodynamics, because Accelerated movement (including electrons around the circle) is accompanied by em-wave radiation. Consequently, the electron gradually loses its energy and should fall on the core. In fact, neither radiation nor the inclination of the electron occurs. An explanation of this was given by N. Blood, having put forward two postulates - the atomic system can only be in some certain states, in which the light is not racing, although the movement accelerated occurs, and when switching from one state to another, the quantum occurs, or the emission of the quantum by law where a constant plank is. Different possible stationary states are determined from the ratio where n. - integer. For the motion of an electron around the circumference in the hydrogen atom, an expression is fair, the Coulomb force of interaction with the kernel. From here. Those. Due to the postulate boron about energy quantization, the movement is possible only in stationary circular orbits, the radii of which are defined as. All states, except for one, are stationary conditionally, and only in one - main in which the electron has a minimal reserve of energy - an atom can be arbitrarily for a long time, and the remaining states are called excited. 70. Emptying and absorption of light by atoms. Laser. Atoms can spontaneously emit light quanta, while it passes incoherent (because each atom radiates independently of others) and is called spontaneous. The electron transition from the top level to the lower may occur under the influence of an external electromagnetic field with a frequency equal to the transition frequency. Such radiation is called forced (induced). Those. As a result of the interaction of the excited atom with the photon of the corresponding frequency, the likelihood of two identical photons with the same direction and frequency is high. A feature of induced radiation is that it is monochromatic and coherently. This property is based on the action of lasers (optical quantum generators). In order for the substance to increase the light passing through it, it is necessary that more than half of its electrons are in the excited state. This condition is called a state with inverse population levels. In this case, the absorption of photons will be less common than emission. To work a laser on a ruby \u200b\u200brod is used by the so-called. A pump lamp, the meaning of which is to create an inverse population. At the same time, if one atom proceeds from a metastable state to the main one, the chain reaction of photon emission will arise. With the corresponding (parabolic) form of a reflective mirror, it is possible to create a beam in one direction. The complete flashing of all excited atoms occurs for 10 -10 s, so the laser power reaches billions of watts. There are also lasers on gas lamps, the advantage of which is the continuity of radiation. 70. The composition of the atom nucleus. Isotopes. The binding energy of atomic nuclei. Nuclear reactions. Electric Hone Atom Cap q. equal to the product of elementary electric charge e. On the sequence number Z. Chemical element in the Mendeleev table. Atoms having the same structure have the same electronic shell and chemically indistinguishable. In nuclear physics, use their units of measurement. 1 Fermi is 1 femetometer ,. 1 Atomic unit of mass - 1/12 mass of carbon atom. . Atoms with the same nucleus charge, but various masses are called isotopes. Isotopes differ in their spectra. The kernel of the atom consists of protons and neutrons. The number of protons in the kernel is equal to the charge number Z., number of neutrons - mass minus the number of protons A - z \u003d n. The positive charge of the proton is numerically equal to the charge of an electron, the proton mass - 1.007A.E.M. The neutron does not have a charge and has a lot of 1.009A.M. (The neutron is heavier than the proton more than two electronic masses). Neutrons are stable only in the composition of atomic nuclei, they live in free form ~ 15 minutes and disintegrate into proton, electron and antineutrino. The strength of the gravitational attraction between nucleons in the nucleus exceeds the electrostatic force of the repulsion of 10 36 times. The stability of the nuclei is explained by the presence of special nuclear forces. At a distance of 1 fm from the proton, nuclear forces are 35 times higher than Coulomb, but very quickly decrease, and at a distance of about 1.5 fm, they can be neglected. Nuclear forces do not depend on whether the particle has a charge. The accurate measurements of the masses of atomic nuclei showed the presence of a difference between the mass of the nucleus and the algebraic sum of the masses of its nucleons. To divide the atomic nucleus to the components, it is necessary to spend energy. The value is called a mass defect. The minimum energy that should be spent on the separation of the kernel into the components of its nucleons is called the core binding energy consumed to perform work against the nuclear forces of attraction. The ratio of communication energy to a mass number is called specific communication energy. A nuclear reaction is called the conversion of the initial atomic nucleus when interacting with any particle to another different from the original. As a result of a nuclear reaction, particles or gamma quanta can be emitted. Nuclear reactions are of two types - for the implementation of some, it is necessary to spend energy, with others, energy is released. Released energy is called a nuclear reaction yield. With nuclear reactions, all conservation laws are performed. The law of preservation of the moment of impulse takes the form of the law of preserving the back. 71. Radioactivity. Types of radioactive radiation and their properties. The kernels possess the ability to spontaneously decay. At the same time, only those kernels that have minimal energy compared to those in which the kernel can turn spontaneously to turn into a core. The kernels in which protons are larger than neutrons are unstable, because Increases the Coulomb Sinuction. Kernels in which more neutrons are also unstable, because The neutron mass is greater than the mass of the proton, and the increase in mass leads to an increase in energy. The nuclei can be released from excessive energy or dividing to more stable parts (alpha decay and division), or by changing the charge (beta decay). The alpha decay is the spontaneous division of the atomic nucleus on the alpha particle and the core product. Alpha decay is subject to all elements heavier than uranium. The ability of the alpha particle to overcome the attraction of the nucleus is determined by the tunnel effect (Schrödinger equation). With alpha decay, not all the kernel energy turns into the kinetic energy of the movement of the nucleus and alpha particle. Part of the energy can go on the excitation of the nucleus of the product. Thus, after some time after the collapse, the core of the product emits several gamma quanta and comes to normal. There is also another type of decay - spontaneous division of the nuclei. The easiest element capable of such a decay is uranium. Decay occurs by law where T. - half-life, constant for this isotope. Beta decay is the spontaneous conversion of the atomic nucleus, as a result of which its charge increases by one by emitting an electron. But the neutron mass exceeds the sum of the mass of the proton and electron. This is explained by the release of another particle - electronically antineutrino . Not only neutron is able to disintegrate. The free proton is stable, but when exposed to particles, it can break through the neutron, positron and neutrino. If the energy of the new nucleus is less, then there is a positron beta decay . Like alpha decay, beta decay can also be accompanied by gamma radiation. 72. Methods for registering ionizing radiation. The method of photoemulsions is to apply a sample to a photoflastic, and after the manifests of the thickness and length of the trace of the particle on it it is possible to determine the amount and distribution of a radioactive substance in the sample. The scintillation counter is a device in which the conversion of the kinetic energy of a fast particle into the light flash energy, which, in turn, initiates the photo effect (electrical current pulse), which is enhanced and registed. Wilson Camera is a glass chamber with air and forged alcohol couples. When the particle is moving through the chamber, it ionizes the molecules around which condensation immediately begins. The chain of drops formed as a result forms a particle track. The bubble camera works on the same principles, but the liquid close to the boiling point serves as a registrar. The gas-discharge meter (Geiger meter) is a cylinder filled with rarefied gas and a stretched thread from the conductor. The particle causes gas ionization, ions under the action of the electric field are diverted to the cathode and anode, ionizing on the way other atoms. The crown discharge occurs, the pulse of which is recorded. 73. Chain reaction of uranium nuclei. In the 30s, it was experimentally established that during the irradiation of uranium neutrons, Lanthan cores are formed, which could not be formed as a result of alpha or beta decay. The uranium-238 core consists of 82 protons and 146 neutrons. When dividing, exactly in half would have to form praseodymium, but in the stable nucleus of neutron praseodymium 9 less. Therefore, during the division of uranium, other nuclei and excess free neutrons are formed. In 1939, the first artificial division of the uranium core was produced. At the same time, 2-3 free neutron and 200 MeV of energy were distinguished, and about 165 MeV was distinguished in the form of kinetic energies of the shatter or or or. Under favorable conditions, the liberated neutrons can cause divisions of other uranium nuclei. The coefficient of neutron reproduction characterizes how the reaction will occur. If he is more than one. Thus, with each division, the number of neutrons increases, uranium is heated to a temperature of several million degrees, and a nuclear explosion occurs. In the fission factor, a smaller unit, the reaction fades, and at the same unit - is maintained at a constant level, which is used in nuclear reactors. Of the natural isotopes of uranium, only the core is capable of dividing, and the most common isotope absorbs the neutron and turns into plutonium according to the scheme. Plutonium-239 in its properties is similar to uranium-235. 74. Nuclear reactor. Thermonuclear reaction. Nuclear reactors are two species - on slow and fast neutrons. Most of the neutrons released in the division have the energy of about 1-2 MeV, and a speed of about 10 7 m / s. Such neutrons are called rapidly, and equally efficiently absorbed both uranium-235 and uranium-238, and because Heavy isotope is more, and it is not divided, then the chain reaction does not develop. Neutrons moving with speeds about 2h10 3 m / s are called thermal. Such neutrons are more active than fast, absorbed by uranium-235. Thus, for the implementation of a controlled nuclear reaction, neutrons must be slowed down to heat velocities. The most common retarders in reactors are graphite, ordinary and heavy water. In order for the division coefficient to be maintained at the unit level, absorbers and reflectors are used. The absorbers are rods from cadmium and boron, breathtaking thermal neutrons, reflector - beryllium. If used as a fuel to use uranium, enriched with an isotope with a mass of 235, the reactor can operate without a retarder on fast neutrons. In such a reactor, most neutrons are absorbed by uranium-238, which as a result of two beta decays becomes plutonium-239, as well as nuclear fuel and source material for nuclear weapons. Thus, the reactor on fast neutrons is not only an energy installation, but also a combustible combustion unit for the reactor. The disadvantage is the need to enrich uranium with a light isotope. Energy in nuclear reactions is highlighted not only by dividing heavy nuclei, but also by connecting the lungs. To connect the nuclei, it is necessary to overcome the Coulomb force of the repulsion, which is possible at a plasma temperature of about 10,7 -10 8 K. The synthesis of helium from deuterium and tritium or . In the synthesis of 1 gram of helium, an energy equivalent to incineration of 10 tons of diesel fuel is released. The controlled thermonuclear reaction is possible when it is heated to the appropriate temperature by passing an electric current through it or with a laser. 75. The biological effect of ionizing radiation. Radiation protection. The use of radioactive isotopes. The measure of exposure to any radiation for a substance is absorbed dose of radiation. The dose unit is Gray, equal to a dose that the irradiated substance weighing 1 kg is transmitted by energy in 1 joule. Because The physical effect of any radiation on the substance is connected not so much with heating, as with ionization, the unit of exposure dose is introduced, which characterizes the ionization effect of radiation into air. An incidental unit of exposure dose is an x-ray equal to 2.58h10 -4 CL / kg. With an exposure dose of 1 x-rays in 1 cm 3 air contains 2 billion pairs of ions. With the same absorbed dose, the action of various types of irradiation is irradiated. The heavier particle - the stronger its action (however, is heavier and delay easier). The difference in the biological effect of radiation is characterized by a biological efficiency coefficient equal to a unit for gamma rays, 3 for thermal neutrons, 10 for neutrons with an energy of 0.5 MeV. The dose multiplied by the coefficient characterizes the biological effect of the dose and is called an equivalent dose, measured in the zivers. The main mechanism of action on the body is ionization. Ions enter the chemical reaction with the cell and violate its operations, which leads to the death or mutation of the cell. The natural radiation background is an average of 2 mW per year, for cities an additional +1 mW per year. 76. Absolitivity of light speed. Elements hundred. Relativistic dynamics. The experimental way it was found that the speed of light does not depend on which the observer is located in which reference system. It is also impossible to dispersed any elementary particle, for example, an electron, to a speed equal to the speed of light. The contradiction between this fact and the principle of relativity of Galilee was resolved by A. Einstein. The basis of its [special] relativity theory was two postulates: any physical processes proceed equally in various inertial reference systems, the speed of light in vacuo does not depend on the speed of the light source and the observer. The phenomenon described by the theory of relativity is called relativistic. In the theory of relativity, two grades of particles are introduced - those moving with speeds, less fromand with which you can connect the reference system, and those moving with speeds equal fromWith which you can not bind the reference system. Multiplying this inequality () on, we get. This expression is a relativistic rate of addition of speeds, which coincides with Newtonian v.<. For any relative speeds of inertial reference systems V Own time, i.e. That which acts in the reference system associated with a particle is invariant, i.e. It does not depend on the choice of an inertial reference system. The principle of relativity modifies this statement, saying that in each inertial reference system, the time flows the same, but one for all, absolute, time does not exist. The coordinate time is associated with its own time. . Erecting this expression in a square, we get. Magnitude s. Called interval. The consequence of the relativistic rate of the addition of speed is the Doppler effect, which characterizes the change in the frequency of oscillations, depending on the speed of the speed of the wave and observer. When the observer is moving at an angle q to the source, the frequency changes by law . When moving removal from the source, the spectrum shifts to less frequencies corresponding to the greater wavelength, i.e. To the red color, when approaching - to violet. The pulse also varies at speeds close to from:. 77. Elementary particles. Initially, elementary particles were proton, neutron and electron, later - photon. When neutron was discovered - muons and peonies were added to the number of elementary particles. Their mass ranged from 200 to 300 electronic masses. Despite the fact that the neutron disintegrates the duct, electron and neutrinos, there are no these particles inside it, and it is considered an elementary particle. Most elementary particles are unstable, and have a half-life of about 10 -6 -10 -16 s. In the electron movement developed by Dirak, the electron movement in the atom should have been that an electron could have a double with the opposite charge. This particle, detected by cosmic radiation, is called a positron. Subsequently, it was proved that all particles exist their anti-patches, characterized by spin and (if any) charge. There are also true neutral particles that fully coincide with their anti-collies (Pi-zero meson and this null meson). Annihilation phenomenon is the mutual destruction of two anti-particles with energy isolation, for example . According to the law of conservation of energy, the energous energy is proportional to the sum of the masses of the progenicled particles. In accordance with the laws of preservation, the particles never arise one one. Particles are divided into groups, ascending mass - photon, leptons, mesons, baroons. There are 4 types of fundamental (unavail to others) interaction - gravitational, electromagnetic, weak and strong. Electromagnetic interaction is explained by the exchange of virtual photons (from the uncertainty of Heisenberg, it follows that in a short time the electron due to its internal energy can be released quantum, and refund the loss of energy by the capture of the same. The emitted quantum is absorbed by the other, thus ensuring the interaction.), Strong - gluons.) (Spin 1, weight 0, tolerate "color" quark charge), weak - vector bosons. Gravitational interaction is not explained, but the quantum of the gravitational field theoretically must have a lot of 0, spin 2 (???).

The material point is the material point, the concept administered in the mechanics to designate the body, the size and form of which can be neglected. The position of the material point in space is defined as the position of the geometric point. The body can be considered a material point in cases where it moves progressively to large (compared to its dimensions) of the distance; For example, the land with a radius of about 6.4 thousand km is a material point in its annual movement around the Sun (the radius of the orbit - the so-called ecliptic is about 150 million km). Similarly, the concept of the material point is applicable, if the rotational part of the body movement can not be taken into account in the conditions of the problem under consideration (for example, to neglect the daily rotation of the Earth when studying the annual movement).

Modern encyclopedia. 2000.

Material point

Based on the possibility of localizing the physical items in time and space, in classical mechanics, the study of the laws of movement begins with the most simple case. This case is the movement of the material point. A schematic idea of \u200b\u200ban elementary particle Analytical mechanics forms the prerequisites for presenting the basic laws of speaking.

The material point is an object with an infinitely small size and a finite mass. This idea fully meets the ideas about the discreteness of matter. Previously, physicists tried to determine it as a combination of elementary particles in a state of movement. In this regard, the material point in its dynamics was just the necessary for theoretical constructions tool.

The dynamics of the object under consideration comes from an inertial principle. According to him, the material point, not under the influence of external forces, retains its state of rest (or movement) over time. This position is strict enough.

In accordance with the principle of inertia, the material point (free) moves uniformly and straightforwardly. Considering the special case, in which the speed is zero, it can be said that the object retains the state of rest. In this regard, it can be assumed that the influence of a certain force on the subject is reduced simply to changes in its speed. The simplest hypothesis is the assumption that the change in the speed, which the material point has, is directly proportional to the indicator of force acting on it. In this case, the coefficient of proportionality decreases with increasing inertia.

Natural is the characteristic of the material point using the magnitude of the inertia coefficient - mass. In this case, the main law of the dynamics of the object can be formulated as follows: the reported acceleration at each moment of time is equal to the ratio of force, which acts on the object, to its mass. The deposition of kinematics is thus preceded by the presentation of the dynamics. The mass, which in the dynamics characterizes the material point, is introduced A Posteriori (from experience), while the presence of a trajectory, position, acceleration, speed is allowed by A Priori.

In this connection, the equation of the dynamics of the object argue that the product of the object under consideration on any of the components of its acceleration is equal to the corresponding component of the force acting on the object. Supposed that the force is a known function of time and coordinates, the determination of coordinates for the material point in accordance with the times is carried out by three conventional second-order differential equations in time.

In accordance with a well-known theorem of the mathematical analysis course, the solution of this system of equations is uniquely determined by the reference of the coordinates, as well as their first derivatives in any initial time interval. In other words, with the known position of the material point and its speed at a certain point, it is possible to accurately determine the nature of its movement into all future periods.

As a result, it becomes clear that the classical dynamics of the object under consideration is in absolute compliance with the principle of physical determinism. According to him, the upcoming state (position) of the material world can be predicted in the presence of parameters that determine its position at a certain previous point.

Due to the fact that the size of the material point is infinitely small, its trajectory will be a line that takes only one-dimensional continuum in three-dimensional space. In each portion of the trajectory there is a certain value of the force, which sets the move to the next infinitely small period of time.

/ answers to physics, not all

Question

Mechanics, kinematics, dynamics (definition, task area).

Answer

Mechanics - Science on the general laws of traffic law.

The bodies around us move relatively slowly. Therefore, their movements are subject to Newton's laws. Thus, the scope of classical mechanics is very extensive. And in this area, humanity will always use to describe any body movement by Newton's laws.

Kinematics - This is a section of mechanics that studies methods for describing movements and the relationship between the values \u200b\u200bcharacterizing these movements.

Describe the movement of the body - it means to specify a way to determine its position in space at any time.

Question

Mechanical movement, reference body, reference system, methods for indicating the position of the material point on the coordinate plane, the concept of the kinematic equation of the material point.

Answer

Mechanical movement It is called moving bodies or parts of bodies in space relative to each other over time.

The body relative to which the movement is considered, called body reference.

The combination of the reference body associated with it the coordinate system and the clock call schedule.

Mathematically, the movement of the body (or material point) relative to the selected reference system is described by the equations that establish how the coordinates defining the position of the body (point) in this reference system. These equations are called movement equations. For example, in the Cartesian coordinates x, y, z, the movement of the point is determined by the equations ,,

Ways to indicate the position of the material point on the coordinate plane

Setting point position using coordinates. From the math course, you know that the position of the point on the plane can be set using two numbers, which are called the coordinates of this point. For this, as is well known, it is possible to conduct two intersecting mutually perpendicular axles on the plane, for example, OH and OY axis. The intersection point of the axes is called the beginning of the coordinates, and the axes themselves are coordinate axes.

The coordinates of the point M1 (Fig. 1.2) are xj \u003d 2, Wow - 4; The coordinates of the point M2 are x2 \u003d -2.5, y2 \u003d -3.5.

The position of the point M in space relative to the reference body can be set with the help of three coordinates. To do this, it is necessary through the selected point of the reference body to spend three mutually perpendicular axes OH, OY, OZ. In the resulting coordinate system, the position of the point will be determined by three coordinates x, y, z.

If the number x is positive, then the segment is postponed in the positive direction of the axis OH (Fig. 1.3) (X - O A). If the number x is negative, the segment is postponed in the negative axis direction OH. From the end of this segment, they spend a straight parallel axis Oy, and the segment from the axis oh, corresponding to the number y (y \u003d AB), in the positive direction of the Oy axis, if the number is positive, and in the negative direction of the OY axis, if The number is negative.

Next, from the point in another, the cutting is carried out straight, parallel axis OZ. On this direct, the Xoy coordinate plane lay the segment corresponding to the number 2. Direction, Fig. 1.4 in which this segment is settled, is defined in the same way as in the previous cases.

The end of the third segment is the point whose position is given by the coordinates x, y, z.

To determine the coordinates of this point, it is necessary to carry out in the reverse order of the operation that we carried out by finding the position of this point by its coordinates.

Setting the point position using the radius vector. The position of the point can be set not only with the help of coordinates, but also with the help of the radius vector. Radius-vector is a directed segment conducted from the start of coordinates at this point. _

The radius of the vector is made to designate the letter of the Length of the Ra Dius-vector, or that the same, its module (Fig. 1.4), there is a distance from the origin to the point M.

The position of the point will be determined using the radius-vector only if its module (length) and direction in space are known. Only under this condition we will know in which direction from the start of the coordinates should be postponed with a length of length in to determine the position of the point.

So, the position of the point in space is determined by its coordinates or its radius-vector.

The module and the direction of any vector find on its projections on the axis of coordinates. To understand how this is done, it is first necessary to answer the question: What do you understand under the projection of the vector on the axis?

Omit from the beginning A and end in the vector and perpendicular to the axis oh.

Points AJ and inj There are projections, respectively, the beginning and end of the vector A on this axis.

The projection of the vector and on any axis is called the length of the A1V1 segment between the projections of the beginning and end of the vector on this axis, taken with the "+" or "-" sign.

The projection of the vector We will denote the same letter as the vector, but, first, without an arrow above it and, secondly, with an index at the bottom, indicating which the axis is projected by the vector. So, ah and ay - the projections of the vector A on the axis of the coordinate Oh and Oy.

According to the definition of the vector projection on the axis, it can be written: ah \u003d ± i ajej.

The projection of the vector on the axis is an algebraic value. It is expressed in the same units as the vector module.

We agree to consider the projection of the vector on the axis positive, if from the projection of the beginning of the vector to the projection of its end it is necessary to go in the positive direction of the axis of projections. Otherwise (see Fig. 1.5) it is considered negative.

Figures 1.5 and 1.6 It is not difficult to see that the projection. The vector on the axis will be positive when the vector is an acute angle with the direction of the axis of projections, and negative when the vector is with the direction axis of the projections of a dull angle.

The position of the point in space can be set using coordinates or radius-vector connecting the origin and point.

Ways to describe movement. Reference system

If the body can be considered a point, then to describe its movement you need to learn how to calculate the position of the point at any time relative to the selected reference body.

There are several ways to describe, or that the same, tasks, point movement. Consider two of them that are most often applied.

Coordinate method. We will specify the position of the point using coordinates (Fig. 1.7). If the point moves, its coordinates vary over time.

Since the coordinates of the point depend on the time, then we can say that they are the functions of time. Mathematically, it is customary to record as

(1.1)

Equations (1.1) are called kinematic equations of motion of the point recorded in the coordinate form. If they are known, then for each moment of time we will be able to calculate the coordinates of the point, and therefore its position relative to the selected reference body. The form of equations (1.1) for each specific movement will be quite defined.

The line on which the point is moving in space is called the trajectory.

Depending on the form of the trajectory, all movement points are divided into straight and curvilinear. If the trajectory is a straight line, the movement of the point is rectilinear, and if the curve is curvilinear.

Vector method. The position of the point can be specified, as is well known, and with the help of the radius vector. When the material point is moved, the radius-vector determining its position changes over time (rotated and changes the length; Fig. 1.8), i.e. is a function of time:

The last equation is the law of movement of the point recorded in vector form. If it is known, then we can calculate the radius-vector point for any point in time, and therefore determine its position. Thus, the task of three scalar equations (1.1) is equivalent to the task of one vector equation (1.2).

The kinematic equations of motion recorded in the coordinate or vector form allow you to determine the position of the point at any time.

Question

Trajectory, path, moving.

Answer

The material point trajectory is a line in space, which is a set of points in which it was located, is or a material point will be located in its displacement in space relative to the selected reference system. It is essential that the concept of the trajectory has a physical meaning even in the absence of any movement on it. The path is clearly clearly illustrated by the Bobsley's track. (If, under the conditions of the task, it is possible to neglect its width). And it is the highway, and not the bean himself.

It is customary to describe the trajectory Material point in a detrimental coordinate system with a radius vector, direction, length and the initial point of which depend on time. In this case, the curve described by the end of the radius-vector in space can be represented as a conjugate arc of various curvatures that are in the general case in intersecting planes. At the same time, the curvature of each arc is determined by its radius of curvature directed towards the arc from the instantaneous turning center located in the same plane as the arc itself. When the straight line is considered as a limiting case of a curve, the radius of curvature of which can be considered equal to infinity. And therefore the trajectory in the general case can be represented as a set of conjugate arcs.

It is essential that the form of the trajectory depends on the reference system elected to describe the motion of the material point. Thus, a straightforward uniformly accelerating movement in one inertial system in the general case will be parabolic in another uniformly moving inertial reference system.

Speed \u200b\u200bmaterial Points are always aimed at the tangent of the arc used to describe the trajectory of the point. In this case, there is a link between the speed of speed, the normal acceleration and the radius of the curvature of the trajectory at this point:

However, not all movement with a certain speed along the curve of the known radius and the normal (centripetal) acceleration (centripetal), found according to the above formula, is associated with the manifestation of power aimed at normal to the trajectory (centripetal force). So, found according to the photographs of the daily movement shone the acceleration of any of the stars does not talk about the existence of this acceleration of the force attracting it to the polar star, as the center of rotation.

The path is the length of the material point trajectory in physics.

Moving (in kinematics) is a change in the location of the physical body in space relative to the selected reference system. Also moving is called a vector characterizing this change. It has the property of additivity. The length of the segment is the movement module, in the international system of units (C) is measured in meters.

You can define moving as a change in the radius-vector point :.

The movement module coincides with the passage passed in that and only if the speed direction does not change when driving. At the same time, the trajectory will be a straight line. In any other case, for example, in curvilinear movement, it follows from a triangle inequality that the path is strictly greater.

Instant point speed is defined as the limit of the relationship of the movement to a small period of time for which it is performed. More strictly:

Watch VoteDee ...................................................... ..

Question

Speed, average speed, instantaneous speed, kinematic equation for uniform rectilinear movement.

Answer

Speed \u200b\u200b(often referred to, from English. Velocity or Fr. vitesse) - vector physical quantity characterizing the speed of movement and direction of motion of the material point relative to the selected reference system; By definition, equal to the derivative of the radius-vector point in time. The same word is also called a scalar value - either the velocity vector module, or the algebraic velocity of the point, i.e. the projection of this vector on the tangent to the point trajectory

The average speed is in kinematics, some averaged characteristic of the speed of a moving body (or material point). There are two basic definitions of average speed, corresponding to the consideration of the speed of as a scalar or vector value: the average track speed (scalar value) and the average speed of movement (vector quantity). In the absence of additional clarifications, an average travel speed is usually understood at average speed.

You can also enter the average speed of movement, which will be a vector equal to the ratio of the time for which it is committed

The speed of the uniform straight line of the body is called the value equal to the ratio of its movement to the period of time during which this movement occurred.

Instant speed - instantaneous speed is called the ratio of changes in the coordinate point to the time interval, for which this change occurred, at the time interval, seeking to zero.

The geometric meaning of the instantaneous speed is the tilt factor towards the schedule of the law of the movement.

Thus, we "tied" the value of instantaneous speed to a specific point time - set the speed value at the moment of time, at this point of space. Thus, we have the opportunity to consider body speed as a function of time, or the function of the coordinate.

Acceleration, average acceleration Instant acceleration, normal acceleration, tangential acceleration, kinematic equation for equally referred movement.

Answer

Question

Free drop body. Acceleration of gravity.

Answer

in addition, a movement is called a movement that would make the body only under the influence of gravity without taking into account the resistance of the air. With a free falling of the body with a small height of H from the surface of the Earth (H "RZ, where Rz is the radius of the Earth), it moves with a constant acceleration G, directed vertically down.

Acceleration G is called the acceleration of free fall. It is the same for all bodies and depends only from height above sea level and from geographic latitude. If at the time of the start of the time (T0 \u003d 0) the body had a velocity V0, then after an arbitrary period of time Δt \u003d T - T0, the body speed with a free drop will be: V \u003d V0 + G · t.

The path h passed by the body in a free fall, by the time T:

The body velocity module after passing in the free fall of the path h is from the formula:

Because vk2-v02 \u003d 2 · g · h then

The duration Δt of free fall without the initial speed (V0 \u003d 0) from the height H:

Example 1. The body falls vertically down from a height of 20 m without initial speed. Determine:

1) the path h, passed by the body for the last second of the fall,

2) the average rate of falling VSR,

3) middle speed in the second half of the VSR2 path.

Question

The main positions of molecular kinematic theory.

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The concept of a molecule, a atomic unit of mass, the relative molecular weight of atoms and molecules (Mr.), the amount of substance, constant avogadro, molar mass.

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Perfect gas. The main equation of molecular - kinetic theory of perfect gas.

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The equation of the state of the ideal gas (the Mendeleev equation is Klapairone).

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Isothermal, isochran and isobaric processes.

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Electrical charge and its properties.

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Question

The law of the coulon.

Question

Electric field. Electric field strength.

Answer

Question

Work of the field forces when traveling charge. Potential and potential difference.

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Question

Laws of geometric optics, absolute refractive index of light. Relative refractive index of light.

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Question

Thin lenses, thin lens formula.

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Lens - a vitreous body bounded by one or two spherical surfaces.

Material point??

Valentina

The standard definition of the material point in the mechanics is a model of the object, the sizes of which, when solving the problem, can be neglected. However, it can be more clearly to say: the material point is a model of a mechanical system, which has only progressive, but not internal degrees of freedom. This automatically means the inability of the material point to deform and rotation. The mechanical energy can be stored in the material point only in the form of the kinetic energy of the forward movement or the potential energy of interaction with the field, but not in the form of rotation or deformation. In other words, the material point is the simplest mechanical system, which has the minimum possible number of degrees of freedom. The material point may have a mass, charge, speed, impulse, energy.
The accuracy of this definition is visible from such an example: in a sparse gas at high temperature, each molecule is very small compared to the typical distance between molecules. It would seem that they can be neglected and considered a material point molecule. However, this is not so: oscillations and rotation of the molecule are an important tank of "internal energy" of the molecule, the "capacity" of which is determined by the dimensions of the molecule.