An electron that has flown into the gap between A magnetic field

364. The figure shows a coil of wire through which an electric current flows in the direction indicated by the arrow. The coil is located in the plane of the drawing. At the center of the coil, the current magnetic field induction vector is directed

365. Two thin straight conductors parallel to each other carry equal currents. I(see picture). What is the direction of the magnetic field they create at point C?

366. What needs to be done in order to change the poles of the magnetic field of a coil with current?

1) reduce the current strength 2) change the direction of the current in the coil

3) turn off the current source 4) increase the current

367.

368. A permanent bar magnet was brought to a magnetic needle (the north pole is shaded, see figure), which can rotate around a vertical axis perpendicular to the plane of the drawing. While the arrow

369. With what force does a uniform magnetic field with an induction of 2.5 T act on a conductor 50 cm long, located at an angle of 30 ° to the induction vector, with a current strength in the conductor of 0.5 A:

1) 31.25 N; 2) 54.38 N; 3) 0.55 N; 4) 0.3125 N?

371. An electric circuit consisting of four rectilinear horizontal conductors (1 - 2, 2 - 3, 3 - 4, 4 - 1) and a constant current source is in a uniform magnetic field, the magnetic induction vector of which is directed horizontally to the right (see figure, view above). Where is the Ampere force caused by this field, acting on conductor 1 - 2, directed?

372. What is the direction of the Ampere force acting on conductor No. 1 from the other two (see figure), if all the conductors are thin, lie in the same plane, parallel to each other and the distances between adjacent conductors are the same? (I - current strength.)

373. A section of a conductor 10 cm long is in a magnetic field with an induction of 50 mT. The Ampere force when moving the conductor 8 cm in the direction of its action does the work of 0.004 J. What is the strength of the current flowing through the conductor? The conductor is located perpendicular to the lines of magnetic induction.

375. An electron e and a proton p fly into a uniform magnetic field perpendicular to the magnetic induction vector with velocities 2v and v, respectively. The ratio of the modulus of the force acting on the electron from the magnetic field to the modulus of the force acting on the proton at this moment of time is equal to

377. The electron e - , flown into the gap between the poles of the electromagnet, has a horizontal speed perpendicular to the magnetic field induction vector (see figure). Where is the Lorentz force acting on it?

378. The electron e - , which has flown into the gap between the poles of an electromagnet, has a horizontally directed velocity perpendicular to the magnetic field induction vector (see figure). Where is the Lorentz force acting on it directed?

379. Ion Na + mass m flies into the magnetic field with a speed perpendicular to the lines of magnetic field induction and moves along an arc of a circle of radius R. The modulus of the magnetic field induction vector can be calculated using the expression

380. Two initially resting electrons are accelerated in an electric field: the first in a field with a potential difference U, the second - 2U. The accelerated electrons fall into a uniform magnetic field, the lines of induction of which are perpendicular to the speed of the electrons. The ratio of the radii of curvature of the trajectories of the first and second electrons in a magnetic field is

For this task you can get 1 point on the exam in 2020

Task 13 of the USE in physics is devoted to all processes in which the electric and magnetic fields are involved. This is one of the most extensive questions in terms of the number of training topics covered. So, the student may come across the topic "Coulomb's Law, the intensity and potential of the electric field", and he will find the potential difference between the points of the field, the force of interaction between bodies or the voltage applied to the ends of the conductor.

The topic of task 13 of the Unified State Examination in physics may also relate to the magnetic flux and imply the calculation of the modulus of the magnetic field induction vector or its direction. Some of the questions are devoted to the calculation of the Ampère force and the Lorentz force.

Task number 13 of the exam in physics implies a short answer to your question. At the same time, some of the options require recording the numerical value of the value (with rounding to the required fractions if the answer is a decimal fraction), and in the other part, the student will have to choose one of the four proposed answers that he considers correct. Since the time for passing the entire test is limited to a certain number of minutes, it is not worth dwelling on the thirteenth question for a long time. If it causes difficulties, it is better to leave it at the very end of the examination time.

"Physics Magnetic fields" - Magnetic field. What are ions? Let's remember! Electrons are found in metals and alloys in a free state. If there is an electric current, there is a magnetic field. Electric field. In solutions, substances break down into positive and negative ions. Movement away from you. Direction of magnetic lines.

"Magnetic field and its graphic representation" - Biometrology. Polar Lights. magnetic lines. Earth's magnetic field. Opposite magnetic poles. magnetic poles. The magnetic field of permanent magnets. concentric circles. A magnetic field. Inside the bar magnet. Inhomogeneous magnetic field. Ampère's hypothesis. Magnetic field and its graphic representation.

"Physics of the magnetic field" - Acquaintance with the principle of operation of the electric motor. A magnetic needle is located near the straight wire. Creation of an electromagnet. There is a force field in the space around the current-carrying wire. The method of lines of force. Let us explain the strengthening of the magnetic field. Approximately count the number of magnetized carnations.

"Magnetic field physics lesson" - Systematize the concept of "magnetic field" in terms of ideas of an ideological nature. To form the concept of the magnetic field of electric current. Physics lesson on the topic "magnetic field current." Repetition assignments. Frontal experiment using the search method. What changed? Check and conclude.

"Magnetic field energy" - Scalar value. Magnetic field energy density. Electrodynamics. Extracurrents in a circuit with inductance. Permanent magnetic fields. Pulsed magnetic field. Transition processes. Energy density. Calculation of inductance. Relaxation time. Self-induction. Definition of inductance. coil energy. Oscillatory circuit.

"Magnetic field grade 9" - Such a field is called inhomogeneous. Consider the pattern of magnetic field lines of a permanent bar magnet shown in the figure. The circle indicates the cross section of the conductor. Homogeneous and inhomogeneous magnetic field. The figure shows a section of such a conductor, located perpendicular to the plane of the drawing.

Decision. The descent time is .

Correct answer: 4.

A2. Two bodies are moving in an inertial frame of reference. The first body of mass m force F reports acceleration a. What is the mass of the second body if half the force gave it 4 times the acceleration?

Decision. The mass can be calculated using the formula . Twice as little force imparts 4 times more acceleration to a body with mass .

Correct answer: 2.

A3. At what stage of the flight will weightlessness be observed in a spacecraft that becomes a satellite of the Earth in orbit?

Decision. Weightlessness is observed in the absence of all external forces, with the exception of gravitational ones. In such conditions, the spacecraft is located during orbital flight with the engine turned off.

Correct answer: 3.

A4. Two balls of masses m and 2 m moving at speeds equal to 2 v and v. The first ball moves after the second and, having caught up, sticks to it. What is the total momentum of the balls after impact?

Decision. According to the conservation law, the total momentum of the balls after the impact is equal to the sum of the momentum of the balls before the collision: .

Correct answer: 4.

A5. Four equal sheets of plywood L each connected in a stack float in the water so that the water level corresponds to the border between the two middle sheets. If another sheet of the same type is added to the stack, the insertion depth of the sheet stack will increase by

Decision. The immersion depth is half the height of the stack: for four sheets - 2 L, for five sheets - 2.5 L. The immersion depth will increase by .

Correct answer: 3.

A6. The figure shows a graph of the change over time in the kinetic energy of a child swinging on a swing. At the moment corresponding to the point A on the graph, its potential energy, counted from the equilibrium position of the swing, is equal to

Decision. It is known that in the equilibrium position, a maximum of kinetic energy is observed, and the difference in potential energies in two states is equal in absolute value to the difference in kinetic energies. It can be seen from the graph that the maximum kinetic energy is 160 J, and for the point BUT it is equal to 120 J. Thus, the potential energy, counted from the equilibrium position of the swing, is equal to.

Correct answer: 1.

A7. Two material points move along circles with radii and with the same absolute speeds. Their periods of revolution in circles are related by the relation

Decision. The period of revolution around the circle is . Because , then .

Correct answer: 4.

A8. In liquids, particles oscillate around their equilibrium position, colliding with neighboring particles. From time to time the particle makes a "jump" to another equilibrium position. What property of liquids can be explained by this nature of particle motion?

Decision. This nature of the movement of fluid particles explains its fluidity.

Correct answer: 2.

A9. Ice at a temperature of 0 °C was brought into a warm room. The temperature of the ice before it melts

Decision. The temperature of the ice before it melts will not change, since all the energy received by the ice at this time is spent on the destruction of the crystal lattice.

Correct answer: 1.

A10. At what humidity is it easier for a person to endure high air temperature and why?

Decision. It is easier for a person to tolerate high air temperature at low humidity, since the sweat evaporates quickly.

Correct answer: 1.

A11. The absolute body temperature is 300 K. On the Celsius scale, it is

Decision. On the Celsius scale, it is .

Correct answer: 2.

A12. The figure shows a graph of the dependence of the volume of an ideal monatomic gas on pressure in process 1–2. In this case, the internal energy of the gas increased by 300 kJ. The amount of heat imparted to the gas in this process is

Decision. The efficiency of a heat engine, the useful work it does, and the amount of heat received from the heater are related by the equation , whence .

Correct answer: 2.

A14. Two identical light balls, the charges of which are equal in modulus, are suspended on silk threads. The charge of one of the balls is indicated in the figures. Which picture(s) correspond(s) to the situation when the charge of the 2nd ball is negative?

Decision. The indicated charge of the ball is negative. Charges of the same name repel each other. Repulsion is observed in the figure A.

Correct answer: 1.

A15.α-particle moves in a uniform electrostatic field from a point A exactly B along trajectories I, II, III (see Fig.). The work of the forces of the electrostatic field

Decision. The electrostatic field is potential. In it, the work to move the charge does not depend on the trajectory, but depends on the position of the start and end points. For the drawn trajectories, the start and end points coincide, which means that the work of the electrostatic field forces is the same.

Correct answer: 4.

A16. The figure shows a graph of the dependence of the current in the conductor on the voltage at its ends. What is the resistance of the conductor?

Decision. In an aqueous salt solution, the current is created only by ions.

Correct answer: 1.

A18. Electron, flown into the gap between the poles of an electromagnet, has a horizontally directed speed, perpendicular to the magnetic field induction vector (see. Fig.). Where is the Lorentz force acting on the electron directed?

Decision. Let's use the "left hand" rule: let's point four fingers of the hand in the direction of the electron movement (away from us), and turn the palm so that the magnetic field lines enter it (to the left). Then the protruding thumb will show the direction of the acting force (it will be directed downwards), if the particle were positively charged. The electron charge is negative, which means that the Lorentz force will be directed in the opposite direction: vertically upwards.

Correct answer: 2.

A19. The figure shows a demonstration of the experience of checking the Lenz rule. The experiment is carried out with a solid ring, and not a cut one, because

Decision. The experiment is carried out with a solid ring, because an induction current occurs in a solid ring, but not in a cut one.

Correct answer: 3.

A20. The decomposition of white light into a spectrum when passing through a prism is due to:

Decision. Using the formula for the lens, we determine the position of the image of the object:

If the plane of the film is placed at this distance, then a clear image will be obtained. It can be seen that 50 mm

Correct answer: 3.

A22. The speed of light in all inertial frames of reference

Decision. According to the postulate of the special theory of relativity, the speed of light in all inertial frames of reference is the same and does not depend on either the speed of the light receiver or the speed of the light source.

Correct answer: 1.

A23. Beta radiation is

Decision. Beta radiation is a stream of electrons.

Correct answer: 3.

A24. The thermonuclear fusion reaction proceeds with the release of energy, while:

A. The sum of the charges of the particles - the products of the reaction - is exactly equal to the sum of the charges of the original nuclei.

B. The sum of the masses of particles - reaction products - is exactly equal to the sum of the masses of the original nuclei.

Are the above statements true?

Decision. The charge is always stored. Since the reaction proceeds with the release of energy, the total mass of the reaction products is less than the total mass of the initial nuclei. Only A is true.

Correct answer: 1.

A25. A 10 kg mass is applied to a movable vertical wall. The coefficient of friction between the load and the wall is 0.4. With what minimum acceleration must the wall be moved to the left so that the load does not slide down?

Decision. In order for the load not to slide down, it is necessary that the friction force between the load and the wall balance the force of gravity: . For a load that is stationary relative to the wall, the relation is true, where μ is the coefficient of friction, N is the reaction force of the support, which, according to Newton's second law, is related to the acceleration of the wall by the equality . As a result, we get:

Correct answer: 3.

A26. A plasticine ball weighing 0.1 kg flies horizontally at a speed of 1 m/s (see Fig.). It hits a stationary trolley with a mass of 0.1 kg, attached to a light spring, and sticks to the trolley. What is the maximum kinetic energy of the system during its further oscillations? Ignore friction. The impact is considered instantaneous.

Decision. According to the law of conservation of momentum, the speed of a trolley with a sticky plasticine ball is

Correct answer: 4.

A27. Experimenters pump air into a glass vessel while simultaneously cooling it. At the same time, the air temperature in the vessel decreased by 2 times, and its pressure increased by 3 times. By how much did the mass of air in the vessel increase?

Decision. Using the Mendeleev-Clapeyron equation, you can calculate the mass of air in a vessel:

.

If the temperature decreased by 2 times, and its pressure increased by 3 times, then the mass of air increased by 6 times.

Correct answer: 3.

A28. A rheostat was connected to a current source with an internal resistance of 0.5 ohms. The figure shows a graph of the dependence of the current in the rheostat on its resistance. What is the EMF of the current source?

Decision. According to Ohm's law for a complete circuit:

.

With external resistance equal to zero, the EMF of the current source is found by the formula:

Correct answer: 2.

A29. A capacitor, an inductor and a resistor are connected in series. If, at a constant frequency and amplitude of the voltage at the ends of the circuit, the capacitance of the capacitor is increased from 0 to , then the amplitude of the current in the circuit will be

Decision. The resistance of the circuit to alternating current is . The amplitude of the current in the circuit is

.

This dependence as a function With on the interval has a maximum at . The amplitude of the current in the circuit will first increase, then decrease.

Correct answer: 3.

A30. How many α- and β-decays should occur during the radioactive decay of the uranium nucleus and its final transformation into a lead nucleus?

Decision. During α-decay, the mass of the nucleus decreases by 4 amu. e. m., and during β-decay, the mass does not change. In a series of decays, the mass of the nucleus decreased by 238 - 198 = 40 AU. e.m. For such a decrease in mass, 10 α-decays are required. During α-decay, the nuclear charge decreases by 2, and during β-decay, it increases by 1. In a series of decays, the nuclear charge decreased by 10. For such a decrease in charge, in addition to 10 α-decays, 10 β-decays are required.

Correct answer: 1.

Part B

IN 1. A small stone thrown from a flat horizontal surface of the earth at an angle to the horizon fell back to the ground after 2 s at 20 m from the place of the throw. What is the minimum speed of the stone during the flight?

Decision. In 2 s, the stone traveled 20 m horizontally, therefore, the component of its velocity directed along the horizon is 10 m/s. The speed of the stone is minimal at the highest point of flight. At the top, the total velocity coincides with its horizontal projection and, therefore, is equal to 10 m/s.

IN 2. To determine the specific heat of melting of ice, pieces of melting ice were thrown into a vessel with water with continuous stirring. Initially, the vessel contained 300 g of water at a temperature of 20 °C. By the time when the ice stopped melting, the mass of water increased by 84 g. Determine the specific heat of ice melting from the experimental data. Express your answer in kJ/kg. Ignore the heat capacity of the vessel.

Decision. The water gave off heat. This amount of heat was used to melt 84 g of ice. The specific heat of melting of ice is equal to .

Answer: 300.

IN 3. In electrostatic shower treatment, a potential difference is applied to the electrodes. What charge passes between the electrodes during the procedure, if it is known that the electric field does work equal to 1800 J? Express your answer in mC.

Decision. The work of the electric field to move the charge is . How can you express charge?

.

AT 4. A diffraction grating with a period is located parallel to the screen at a distance of 1.8 m from it. What order of magnitude of the maximum in the spectrum will be observed on the screen at a distance of 21 cm from the center of the diffraction pattern when the grating is illuminated by a normally incident parallel beam of light with a wavelength of 580 nm? Think .

Decision. The deflection angle is related to the grating constant and the wavelength of light by the equality . The deviation on the screen is . Thus, the order of the maximum in the spectrum is

Part C

C1. The mass of Mars is 0.1 of the mass of the Earth, the diameter of Mars is half that of the Earth. What is the ratio of the periods of revolution of artificial satellites of Mars and the Earthmoving in circular orbits at low altitude?

Decision. The period of revolution of an artificial satellite moving around the planet in a circular orbit at a low altitude is equal to

where D- the diameter of the planet, v- the speed of the satellite, which is related to the centripetal acceleration ratio.