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Electromagnetic induction. Electromagnetic vibrations The purpose of this test is to test the student's ability. Tasks: Educational: find out how the induction current is directed in the circuit; formulate Lenz's rule - Lesson

Right hand rule (mainly for determining the direction of magnetic lines
inside the solenoid):

If you grasp the solenoid with the palm of your right hand so that four fingers are directed along the current in the turns, then the set thumb will show the direction of the lines magnetic field inside the solenoid.

Ticket 9: Electromagnetic induction.

The phenomenon of electromagnetic induction

The appearance of an electric current in a closed conducting loop, which either rests in a time-varying magnetic field, or moves in a constant magnetic field so that the number of magnetic induction lines penetrating the loop changes. The faster the number of lines of magnetic induction changes, the more induction current.

Methods for obtaining induction current

...........

MAGNETIC FLUX
(or flux of magnetic induction)

Magnetic flux through a surface of area S is called a value equal to the product of the modulus of the magnetic induction vector B by the area S and the cosine of the angle between vectors B and n.

The magnetic flux is proportional to the number of lines of magnetic induction penetrating the surface of area S.

The magnetic flux characterizes the distribution of the magnetic field over the surface bounded by the contour.

A magnetic flux of 1Wb is created by a uniform magnetic field with an induction of 1T through a surface of 1m2 located perpendicular to the magnetic induction vector.

INDUCTION CURRENT DIRECTION

Straight conductor

The direction of the induction current is determined by the right hand rule:

If you put your right hand so that the magnetic induction vector enters the palm, the thumb set aside 90 degrees indicates the direction of the velocity vector, then straightened 4 fingers will show the direction of the induction current in the conductor.

Closed loop

The direction of the induction current in a closed loop is determined by the Lenz rule.

Lenz's rule

The induction current arising in a closed circuit with its magnetic field counteracts the change in the magnetic flux by which it is caused.

Application of Lenz's rule

1. show the direction of the vector B of the external magnetic field;

2. determine whether the magnetic flux through the circuit increases or decreases;

3. show the direction of the vector Вi of the magnetic field of the induction current (with a decrease in the magnetic flux of the vector В of the external m. Field and Вi of the magnetic field of the induction current should be directed in the same way, and with an increase in the magnetic flux, В and Вi should be directed oppositely);

4. Determine the direction of the induction current in the circuit according to the gimbal's rule.

Ticket 10 Ampere Force Left hand rule.

THE POWER OF AMPERE

This is the force with which a magnetic field acts on a current-carrying conductor.

Ampere's modulus is equal to the product of the current in the conductor by the modulus of the magnetic induction vector, the length of the conductor and the sine of the angle between the vector of magnetic induction and the direction of the current in the conductor.

The ampere force is maximum if the magnetic induction vector is perpendicular to the conductor.

If the magnetic induction vector is parallel to the conductor, then the magnetic field has no effect on the conductor with current, that is, the Ampere force is zero.

Ampere force direction determined by left hand rule:

If left hand position so that the component of the magnetic induction vector perpendicular to the conductor enters the palm, and 4 outstretched fingers are directed in the direction of the current, then the thumb bent 90 degrees will show the direction of the force acting on the conductor with current.

EFFECT OF A MAGNETIC FIELD ON A FRAME WITH A CURRENT

A uniform magnetic field orients the frame (i.e., a torque is created and the frame rotates to a position where the magnetic induction vector is perpendicular to the plane of the frame).

An inhomogeneous magnetic field orientates + attracts or repels the frame with current.

Ticket 11: Lorentz Force Left hand rule

Lorentz force

Force acting from a magnetic field on a moving electrically charged particle.

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The direction of the Lorentz force is determined byleft hand rule:

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Since the Lorentz force is always perpendicular to the velocity of the charge, it does not perform work (i.e., it does not change the magnitude of the velocity of the charge and its kinetic energy).

If a charged particle moves in parallel power lines magnetic field, then Fl \u003d 0, and the charge in the magnetic field moves uniformly and rectilinearly.

If a charged particle moves perpendicular to the lines of force of the magnetic field, then the Lorentz force is centripetal

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In this case, the particle moves in a circle.

According to Newton's second law: the Lorentz force is equal to the product of the particle mass by the centripetal acceleration

then the radius of the circle

and the period of charge revolution in a magnetic field

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On electric chargesmoving with the conductor in a magnetic field, acts
lorentz force:

Fl \u003d / q / vB sin a

q - charge (C)

V - speed (m / s)

B - magnetic induction (T)

Its direction can be determined by the left hand rule.

Under the action of the Lorentz force, the distribution of positive and negative charges along the entire length of the conductor l.
The Lorentz force is in this case an external force, and an EMF of induction arises in the conductor, and a potential difference arises at the ends of the conductor AB.

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2. Indicate the direction of the induction current in the circuit when it is introduced into a uniform magnetic field.

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4. Will there be induction current in the conductors if they move as shown in the figure?

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6. Indicate the correct direction of the induction current in the circuits.

Thermal power engineering "href \u003d" / text / category / teployenergetika / "rel \u003d" bookmark "\u003e the thermal energy of the combusted fuel is used in a steam generator, where a very high steam pressure is reached, which drives the turbine rotor and, accordingly, the generator. such thermal power plants use fuel oil or diesel, and natural gas, coal, peat, shale, in other words, all types of fuel. TPES efficiency is about 40%, and their capacity can reach 3-6 GW.

2.HPP

Hydroelectric power plant (HPP) - a power plant that uses the energy of the water flow as an energy source. Hydroelectric power plants are usually built on rivers by constructing dams and reservoirs.

For the efficient production of electricity at hydroelectric power plants, two main factors are required: guaranteed water availability all year round and possibly large slopes of the river, canyon-like relief types favor hydraulic construction.

Principle of operation

The necessary water pressure is formed by the construction of a dam, and as a result of the concentration of the river in a certain place, or by derivation - by the natural flow of water. In some cases, to obtain the required water pressure, both the dam and the derivation are used together.

All power equipment is located directly in the building of the hydroelectric power station. Depending on the purpose, it has its own specific division. In the machine room there are hydraulic units that directly convert the energy of the water flow into electrical energy. There is also all sorts of additional equipment, control and monitoring devices for the operation of the hydroelectric power station, a transformer station, switchgears and much more.

Hydroelectric stations are divided depending on generated power:

· Powerful - generate from 25 MW and above;

Medium - up to 25 MW;

· Small hydroelectric power plants - up to 5 MW.

The power of a hydroelectric power station depends on the pressure and flow rate of water, as well as on the efficiency of the turbines and generators used. Due to the fact that, according to natural laws, the water level is constantly changing, depending on the season, and also for a number of reasons, it is customary to take cyclic power as an expression of the power of a hydroelectric station. For example, a distinction is made between annual, monthly, weekly or daily cycles of a hydroelectric power plant.

A typical small hydroelectric power station for the mountainous regions of China (Houzibao HPP, Xingshan County, Yichang County, Hubei Province). Water comes from the mountain through a black pipeline

Hydroelectric power plants are also divided according to the maximum use water pressure:

· High-pressure - more than 60 m;

· Medium-pressure - from 25 m;

· Low-pressure - from 3 to 25 m.

3. TPP

Nuclear power plant (NPP) - a nuclear installation for the production of energy in specified modes and conditions of use, located within the territory defined by the project, in which a nuclear reactor (reactors) and a complex of necessary systems, devices, equipment and structures with the necessary workers (personnel )

The principle of operation of nuclear power plants is in many ways similar to the operation of power plants using fossil fuel. The main difference is fuel. The nuclear power plant uses uranium, a pre-enriched natural ore, and steam is produced by nuclear fission, not by burning oil, gas or coal. Nuclear power plants do not burn fuel, so the atmosphere is not polluted. The process is as follows:

Tiny particles of uranium, called atoms, fission.

During fission, even smaller elements of the atom - neutrons - are released.

Neutrons collide with uranium atoms, generating the heat needed to generate electricity.

Ticket 14. Types of ES. The impact of ES on the environment. Wednesday.

The environment is the basis of human life, and fossil resources and the energy generated from them are the basis modern civilization... Without energy, humanity has no future, this is an obvious fact. However, modern energy is causing significant harm to the environment, worsening the living conditions of people. The basis of modern energy is various types of power plants. At the dawn of the development of the domestic industry, 70 years ago, the main stake was made on large TPP... At that time, about the influence of TPP on environment thought little, since the primary task was to obtain electricity and heat. Production technology electrical energy on TPP associated with a large amount of waste released into the environment. Today, the problem of the influence of energy on nature is becoming especially acute, since the pollution of the environment, atmosphere and hydrosphere is increasing every year. If we take into account that the scale of energy consumption is constantly increasing, then the negative impact of energy on nature also increases. If during the formation of energy in our country, first of all, they were guided by expediency from the point of view of economic costs, today, more and more often during the construction and operation of energy facilities, issues of their impact on the environment are brought to the fore.

Thermal power plants run on relatively cheap fossil fuel - coal and fuel oil, these are irreplaceable natural resources. Today, the main energy resources in the world are coal (40%), oil (27%) and gas (21%). According to some estimates, these reserves will last for 270, 50 and 70 years, respectively, provided that the current consumption rates are maintained.

When fuel is burned at TPPs, combustion products are formed, which contain: fly ash, particles of unburned pulverized fuel, sulfuric and sulfurous anhydride, nitrogen oxide, gaseous products of incomplete combustion. When fuel oil is ignited, vanadium compounds, coke, sodium salts, and soot particles are formed. The ash of some fuels contains arsenic, free calcium dioxide, free silicon dioxide, which cause significant harm to all living things.

The environment is also polluted by the industrial waste waters of TPPs containing oil products. The station discharges this water after chemical flushing of equipment, heating surfaces of steam boilers and hydraulic ash removal systems.

Sulfur oxide released into the atmosphere causes great damage to animals and flora, it destroys chlorophyll found in plants, damages leaves and needles. Carbon monoxide, getting into the body of humans and animals, combines with blood hemoglobin, resulting in a lack of oxygen in the body, and, as a result, various disorders of the nervous system occur.

Nitric oxide reduces the transparency of the atmosphere and contributes to the formation of smog. Vanadium pentaxide contained in the ash is highly toxic, if it gets into airways humans and animals, it causes severe irritation, disrupts the activity of the nervous system, blood circulation and metabolism. A peculiar carcinogen, benzopyrene, can cause cancer.

The largest water sector is hydro-power. During the construction of lowland hydroelectric power plants, a negative aspect is the flooding of vast territories. To reduce the area of \u200b\u200bflooded land, it is necessary to build protective dams. It is necessary to monitor the water level in the reservoirs in order to avoid temporary flooding of the banks; to clear the bed of the future reservoir from shrubs, trees, etc. etc .; to create conditions for the development of fisheries in reservoirs, since hydroelectric power plants damage not only agriculture, but also fishing.

All hydroelectric power plants cause colossal damage to fisheries. Previously, events proceeded in a constant evolutionary sequence: spring floods, fish spawning, and fry sliding into the sea. And now hydroelectric power plants violate this order. The flood, called the release of water, occurs in the middle of winter, by spring the ice layer settles on the flooded islands, presses the wintering fish in the wintering pits, disrupting the biological maturation of eggs. This means that it will take two years before the immature caviar dissolves and a new one is laid.

Reservoirs increase the air humidity, contribute to a change in the wind regime in the coastal zone, while at the same time the temperature and ice regime of the drain. This leads to a change natural conditions, which affects the economic activity of the population and the life of animals.

The construction of a hydroelectric power plant should be designed with minimal environmental damage to nature. When developing, it is necessary to rationally choose a quarry, the location of roads, etc. Upon completion of construction, work should be carried out to recultivate the disturbance of the land and landscaping the territory. The most effective environmental protection measure is engineering protection. The construction of dams reduces the area of \u200b\u200bflooded land, keeping it for agricultural use; reduces the area of \u200b\u200bshallow water; preserves natural complexes; improves the sanitary conditions of the reservoir. If the construction of the dam was not economically justified, then the shallow waters can be used for breeding birds or other economic needs.

NUCLEAR PLANT.Usually, when they talk about radiation pollution, they mean gamma radiation, which is easily captured by Geiger counters and dosimeters based on them. At the same time, there are many beta emitters that are poorly detected by existing mass instruments. Just like radioactive iodine is concentrated in thyroid glandcausing its defeat, radioisotopes of inert gases, which in the 70s were considered absolutely harmless to all living things, accumulate in some cellular structures of plants (chloroplasts, mitochondria and cell membranes). One of the main emitted inert gases is krypton-85. The amount of krypton-85 in the atmosphere (mainly due to the operation of nuclear power plants) is increasing by 5% per year. Another radioactive isotope, not captured by any filters and in large quantities produced by any nuclear power plant - carbon-14. There is reason to believe that the accumulation of carbon-14 in the atmosphere (in the form of CO2) leads to a sharp slowdown in tree growth. Now the amount of carbon-14 in the atmosphere has increased by 25% compared to the pre-atomic era.

An important feature of the possible impact of a nuclear power plant on the environment is the need to dismantle and dispose of radioactive equipment elements at the end of their service life or for other reasons. Until now, such operations were carried out only on a few experimental installations.

During normal operation, only a few nuclei of gaseous and volatile elements such as krypton, xenon, iodine enter the environment. Calculations show that even with an increase in the capacity of nuclear power by 40 times, its contribution to global radioactive pollution will be no more than 1% of the level of natural radiation on the planet.

At power plants with boiling boiling reactors (single-circuit), most of the radioactive volatiles are released from the coolant in the turbine condensers, from where, together with the radiolysis gases, water is ejected by ejectors in the form of a vapor-gas mixture into special chambers, boxes or holding gasholders for primary treatment or combustion. The rest of the gaseous isotopes are released during decontamination of solutions in the holding tanks.

In power plants with pressurized water reactors, gaseous radioactive waste is released in holding tanks.

Gaseous and aerosol waste from assembly spaces, boxes of steam generators and pumps, protective covers of equipment, containers with liquid waste are removed using ventilation systems in compliance with the standards for the release of radioactive substances. Most of the aerosols are removed from the air flow from the fans using fabric, fibrous, grain and ceramic filters. Before being discharged into the ventilation pipe, air passes through gas sedimentation tanks, in which short-lived isotopes (nitrogen, argon, chlorine, etc.) decompose.

In addition to emissions associated with radiation pollution, nuclear power plants, like thermal power plants, are characterized by heat emissions that affect the environment. An example is the Vepko Sarri nuclear power plant. Its first unit was commissioned in December 1972, and the second - in March 1973. At the same time, the water temperature near the river surface near the power plant in 1973. was H4єC higher than the 1971 temperature. and the maximum temperatures were observed a month later. Heat is also released into the atmosphere, for which the so-called. cooling towers. They release 10-400 MJ / (m / h) of energy into the atmosphere. The widespread use of powerful cooling towers raises a number of new challenges. The consumption of cooling water for a typical 1100 MW NPP unit with evaporative cooling towers is 120,000 t / h (at an ambient water temperature of 14єC). With normal salt content of the make-up water, about 13.5 thousand tons of salts are released per year, falling onto the surface of the surrounding area. Until now, there is no reliable data on the impact on the environment of these factors.

The NPP provides for measures to completely exclude the discharge of wastewater contaminated with radioactive substances. A strictly defined amount of purified water with a concentration of radionuclides not exceeding the level for drinking water is allowed to be discharged into reservoirs. Indeed, systematic observations of the impact of nuclear power plants on aquatic environment during normal operation, they do not show significant changes in the natural radioactive background. Other waste is stored in containers in liquid form or preliminarily converted into a solid state, which increases storage safety.

Ticket 15: Elements of the industry. electronics - capacitors.

A capacitor is a charge storage device. Consists of two conductors - plates, separated by a dielectric.

Designation in the diagram:

The property of a capacitor to accumulate and retain electrical charges is characterized by its capacity. The greater the capacitance of the capacitor, the greater the charge accumulated by it.

The electrical capacity of a two-conductor system is called physical quantitydefined as the charge ratio q one of the conductors to the potential difference Δφ between them:

The simplest capacitor is a system of two flat conducting plates located parallel to each other at a small distance compared to the dimensions of the plates and separated by a dielectric layer. Such a capacitor is called flat .

Depending on the dielectric used, capacitors are paper, mica, air. Using mica, paper, ceramics and other materials with a high dielectric constant as a dielectric instead of air, it is possible to increase its capacitance several times with the same dimensions of a capacitor. In order to increase the area of \u200b\u200bthe electrodes of the capacitor, it is usually made multilayer.

Power capacitors are usually used in AC electrical installations. In them, long strips of aluminum, lead or copper foil serve as electrodes, separated by several layers of special (capacitor) paper soaked in petroleum oils or synthetic impregnating liquids. Foil strips 2 and paper 1 are wound into rolls (Fig. 185), dried, impregnated with paraffin and placed in one or more sections in a metal or cardboard case. The required operating voltage of the capacitor is provided by serial, parallel or serial-parallel connections of individual sections.

Capacitor connection methods... Capacitors can be connected in series and in parallel. With consistent

Application: Capacitors are used in almost all areas of electrical engineering.

1.Capacitors (together with inductors and / or resistors) are used to build various circuits with frequency-dependent properties, in particular, filters, feedback circuits, oscillatory circuits, etc.

(2) With a rapid discharge of a capacitor, a high-power pulse can be obtained, for example, in photo flashes, electromagnetic accelerators, pulsed optically pumped lasers, Marx generators (GIN; PCG), Cockcroft-Walton generators, etc.

3. Since the capacitor is capable of storing a charge for a long time, it can be used as a memory element or a device for storing electrical energy.

4. Liquid level meter. Non-conductive liquid fills the space between the capacitor plates, and the capacitance of the capacitor changes depending on the level

5. Accumulators of electrical energy. In this case, the capacitor plates must have a sufficiently constant voltage and discharge current. In this case, the discharge itself must be significant in time. Pilot development of electric vehicles and hybrids using capacitors is currently underway. There are also some models of trams in which capacitors are used to power traction motors when driving on de-energized areas.

Ticket 16: Dielectrics

Dielectrics (insulators) - substances that conduct poorly or not at all electricity... Dielectrics include air, some gases, glass, plastics, various resins, and many types of rubber.

shortcodes "\u003e

1) 1 picture. Indicate in which case the phenomenon of electromagnetic induction is observed:

A. At the minimum value of the resistance of the rheostat.
B. With an increase in the resistance of the rheostat.
B. At the maximum value of the resistance of the rheostat.
D. With a constant value of the resistance of the rheostat.

2) What is the energy of the magnetic field of a coil with an inductance of 0.2 H at a current of 3 A?
A. 0.3 J.
B. 0.6 J.
H. 0.8 J.
G. 0.9 J.
D. 1.5 J.

3) Find the end of the statement that most fully reflects the essence of the phenomenon of electromagnetic induction: "In a closed loop, an electric current appears if ..."
A. ... the circuit is in a constant magnetic field.
B. ... the circuit moves in a constant magnetic field.
B. ... the circuit rotates in a constant magnetic field.
G. ... the circuit moves in a constant magnetic field so that the magnitude of the magnetic flux through the circuit changes.

4) Find the change in 3 ms of magnetic flux through a circuit containing 80 turns of 120 ohm wire, if the induction current is 4 A:
A. 1440 mVb.
B. 18 mVb.
V. 90 mVb
G. 1.1 mVb

5) 2 figure. The graphs of the dependence of the magnetic flux penetrating the contour on time are shown. Indicate the case when the EMF of induction increases:
A. 1
B. 2
IN 3.
D. 4.

6) Where in fig. correctly shown the direction of the induction current arising in a closed loop when approaching the south pole of the magnet?
A. 1.
B. 2.
IN 3.
D. 4.

1. The figure shows the direction of the magnetic field lines. In this magnetic field, the closed loop of the wire is moved first

vertically upwards so that the plane of the loop is parallel to the lines of magnetic field induction (in the figure - situation A), then horizontally so that the plane of the loop is perpendicular to the lines of induction of the magnetic field (in the figure - situation B). At what movement of the frame does the magnetic flux change?

1) Only in A 3) Both in A and B

2) Only in B 4) Neither A nor B

2. The closed loop is located at a certain angle to the lines of magnetic induction. How will the magnetic flux change if the modulus of the magnetic induction vector increases by 3 times?

1) Increase 3 times 3) Increase 6 times

2) Decrease 3 times 4) Decrease 9 times

3. The closed loop is located at a certain angle to the lines of magnetic induction. How will the magnetic flux change if the area of \u200b\u200bthe circuit decreases by 2 times, and the modulus of the magnetic induction vector increases 4 times?

1) Will increase 2 times 3) Increase 4 times

2) Decrease by 2 times 4) Decrease by 4 times

4. The lines of magnetic induction lie in the plane of the closed loop. How will the magnetic flux change if the modulus of the magnetic induction vector increases by 3 times?

1) Increase 3 times 3) Increase 9 times

Physics grade 11. Theme:Electromagnetic induction. Electromagnetic vibrations

The purpose of this test is to check if a student can:

Option 1

unfulfilled.

+B. When the key is closed, an induction current arises in the coil for a short time.

–IN. The magnetic field of the induction current is always directed upwards.

–G. The induction current in the coil is always clockwise.

2. The charged capacitor was connected to the inductor. Choose the correct statement.

+A. After some time, the signs of the charges of the capacitor plates will change to the opposite.

–B. The energy of a charged capacitor is the energy of the magnetic field.

–IN. Oscillations of the capacitor charge and the current in the circuit occur in the same phase.

–G. Oscillations in the circuit will stop as soon as the capacitor charge becomes zero.

3. The transformer steps down the voltage from 220 V to 36 V. Choose the correct statement.

–A. The transformer can step down the DC voltage.

–B. The number of turns in the secondary winding is greater than in the primary.

–IN.

+G. EMF in the secondary winding occurs due to the phenomenon of electromagnetic induction.

4. A fixed closed loop is in a changing magnetic field. Note which of the following four statements are correct and which are incorrect.

+A. If the lines of magnetic induction cross the plane of the circuit, an induction current arises in the circuit.

+B. The EMF of induction in a closed loop is the greater, the faster the magnetic flux through this loop changes.

–IN. The magnetic field of the induction current is always directed in the same direction as
like an external magnetic field.

–G. If you open the circuit, the EMF of induction in it will be equal to zero.

5. A 400 pF capacitor and a 25 mH coil form an oscillating circuit. Note which of the following four statements are correct and which are incorrect.

–A. Only direct current can flow in the loop.

–B. The period of free oscillations in the circuit is less than 15 μs.

+IN. The period of free oscillations in the circuit is more than 10 μs.

–G. The oscillation frequency depends on the maximum charge of the capacitor.

6. Four-pole generator alternating current rotates with a frequency of 1500 min –1. Note which of the following four statements are correct and which are incorrect.

+A. To generate the same alternating current, a two-pole generator must rotate at 3000 min –1.

+B. The generator generates alternating current with a frequency of 50 Hz.

–IN. The alternating current period is 10 ms.

+G. The generator converts some type of energy into electrical energy.

8. A charged 10 pF capacitor was connected to the inductor. Chart of further changes in charge q capacitor is shown in the figure. Note which of the following four statements are correct and which are incorrect.

+A. Coil inductance is less than 12 mH.

+B. The amplitude value of the capacitor charge is more than 5 nC.

+IN. The capacitor charge changes according to the law

–G. The maximum voltage across the capacitor is less than 100 V.

9. In a coil of 200 turns, a constant EMF of 160 V was excited for 5 ms. Note which of the following four statements are correct and which are incorrect.

–A. The magnetic flux through the coil did not change.

–B. In 5 ms, the magnetic flux through each loop changed by 0.8 Wb.

–IN. If the rate of change of the magnetic flux is increased by 4 times, the EMF of the induction will increase by 2 times.

–G. EMF of induction in one turn is more than 1 V.

10 ... In a coil with an inductance of 80 mH, the current increased from zero to 1 A in 0.1 s. Note which of the following four statements are correct and which are incorrect.

–A. If the rate of change of the current strength was constant, then the induction EMF in the coil was more than 1 V.

+B. The magnetic field energy of the coil increased to 40 mJ.

+IN. The average current power in the coil exceeded 0.3 W.

–G. If the coil is disconnected from the current source and short-circuited, an amount of heat will be released in it, more than 0.5 J.

11. A 4 nF capacitor was charged to a voltage of 5 V and connected to a coil with an active resistance of 1 Ohm and an inductance of 80 μH. Considering the damping of the resulting free oscillations to be slow, note which of the following four statements are correct and which are incorrect.

–A. The period of free oscillations arising in the chain is more than 4 μs.

–B. The period of free oscillations arising in the chain is more than 5 μs.

–IN. During the period, the vibration energy decreases by more than 5 nJ.

+G. During the period, the vibration energy decreases by more than 1 nJ.

12. To the network alternating voltage 50 Hz, a 100 μF capacitor and a coil are connected in series. The inductance of a coil without a core is 10 mH, and with a fully inserted core, 0.3 H. Note which of the following four statements are correct and which are incorrect.

+A. When there is no core in the coil, its inductive reactance is less than that of the capacitor.

–B. When the core is pulled out of the coil, the current in the circuit decreases all the time.

–IN. When the core is pulled out of the coil, the current in the circuit increases all the time.

+G. If the core is gradually introduced into the coil, the current in the circuit first increases and then decreases.

Option 2

When writing down the answers to the test items, circle the letters that correspond to the statements that you think are correct, and cross out the letters that correspond to the statements that you believe are incorrect. For example, if you think statements A and C are correct and statements B and D are wrong, write it down. If at least one letter out of 4 is not marked, the task is considered unfulfilled.

1. A stationary closed wire frame is located in a uniform changing magnetic field. Choose the correct statement.

+A. If the induction vector of the magnetic field is perpendicular to the plane of the frame, an induction current appears in the frame.

–B. An induction current in the frame occurs at any position of the frame.

–IN. EMF of induction in the frame depends only on the area of \u200b\u200bthe frame.

–G. If the induction vector of the magnetic field is perpendicular to the plane of the frame, the magnetic flux through the plane of the frame is always zero.

2. The oscillating circuit consists of a capacitor and an inductor. Ignore energy loss due to vibrations, choose the correct statement.

–A. Direct current can exist in this circuit.

–B. Only forced electromagnetic oscillations can occur in the circuit.

–IN. The direction of the current in the circuit does not change.

+G. With electromagnetic oscillations in the circuit, the current is maximum at the moment when the capacitor charge is zero.

3. To transmit electricity over a long distance, the voltage is increased using a transformer to 500 kV. Choose the correct statement.

–A. This is done to increase the current in the power line.

–B. This is done only when transferring energy using direct current.

+IN. This is done to reduce transmission losses.

–G. Energy losses in powerful transformers exceed 50%.

4. An induction current has arisen in a fixed closed wire loop. Note which of the following four statements are correct and which are incorrect.

–A. The induction current arose under the influence of Coulomb forces.

–B. The magnetic flux through the loop did not change.

–IN. Free electrons in the wire began to move in an orderly manner under the action of the Lorentz force.

+G. Free electrons in the wire began to move in an orderly manner under the action of a vortex electric field.

5. Free electromagnetic oscillations with a frequency of 100 kHz occur in the oscillatory circuit. Note which of the following four statements are correct and which are incorrect.

+A. The current in the circuit fluctuates at a frequency of 100 kHz.

–B. The charges on the capacitor plates change with a frequency of 50 kHz.

+IN. If the capacitance of the capacitor is 1 μF, then the inductance of the coil is greater than 1.5 μH.

–G. The oscillation period in the loop is 100 μs.

6. An ammeter connected in series with a 20 µF capacitor in a 50 Hz alternating current circuit shows 400 mA. If a capacitor is considered ideal, note which of the following four statements are correct and which are incorrect.

–A. The ammeter shows the amplitude value of the current in the circuit.

+B. No heat is generated when alternating current flows through the capacitor.

+IN. A voltmeter connected in parallel with the capacitor will show a voltage of less than 120 V.

+G. The peak value of the voltage across the capacitor is less than 200 V.

8. With free oscillations in the circuit, the amplitude value of the capacitor charge is 0.2 mC. The capacitance of the capacitor is 20 μF, the inductance of the coil is 4 mH. Assuming the vibration is continuous, note which of the following four statements are correct and which are incorrect.

–A. The natural frequency in the circuit is greater than 1 kHz.

–B. The loop current and capacitor voltage fluctuate in the same phase.

–IN. The voltage across the capacitor exceeds 15 V.

–G. The maximum coil current is less than 500mA.

9. The figure shows the graph i(t) for alternating current. Note which of the following four statements are correct and which are incorrect.

+A. The current period is 4 μs.

+B. The current in the circuit changes according to the law

+IN. If a given alternating current is passed through a 1 μF capacitor, the capacitance of the capacitor is less than 1 ohm.

–G. Effective value current strength less than 8 A.

10 . The figure shows the electrical circuit. Source EMF \u003d 6 V, internal resistance r \u003d 0.5 Ohm, coil inductance L \u003d 0.2 H, resistor resistance R 1 \u003d 2.5 ohms and R 2 \u003d 1 ohm. Do not take into account the active resistance of the coil. The key is closed, and after a long time it is opened. Note which of the following four statements are correct and which are incorrect.

–A. Immediately after closing the key, the current in the resistor R 2 is smaller than the coil.

+B. Before opening the key, the current in the coil is more than 1.5 A.

–IN. After opening the key, an amount of heat more than 1 J.

–G. After opening the key, an amount of heat more than 2 J.

11. In the oscillatory circuit, the capacitance of the capacitor is 50 μF, and the inductance of the coil is 0.2 G. The amplitude value of the current strength is 40 mA. By neglecting the active resistance of the loop, note which of the following four statements are correct and which are incorrect.

+A. The oscillation frequency in the circuit is greater than 40 Hz.

–B. The vibration frequency in the circuit depends on the vibration amplitude.

+IN. The current decreases from 40 mA to 20 mA in 1/6 cycle.

+G. When the current is 30mA, the voltage across the capacitor
more than 1.5 V.

12. A capacitor with a capacity of 1 μF and a coil with an inductance of 0.5 H and an active resistance of 50 Ohm are connected in series to the alternating current circuit. Note which of the following four statements are correct and which are incorrect.

–A. The inductive resistance of the coil at a frequency of 50 Hz is greater than 200 ohms.

+B. At 500 Hz, the inductive reactance of the coil is greater than the capacitance of the capacitor.

+IN. Resonance in this circuit occurs at a frequency less than 300 Hz.

–G. At resonance active resistance the coil makes up more than 15% of its inductive resistance.

Option 3

1. In a conductor moving in a magnetic field, there is an EMF of induction. Choose the correct statement.

–A. EMF of induction depends only on the speed of movement of the conductor.

–B. EMF of induction depends only on the length of the conductor.

+IN. EMF of induction is maximum when the speed of the conductor is perpendicular to both the conductor and the vector of the magnetic field induction.

–G. If you increase the induction of the magnetic field, the EMF of induction
in a moving conductor will decrease.

2. Charged from source constant voltage the capacitor is connected to the inductor using a switch (see figure). Choose the correct statement.

–A. When the capacitor was connected to the source, forced continuous oscillations existed in the circuit.

+B. When the capacitor was connected to the coil, a free vibration occurred in the circuit.

–IN. With electromagnetic oscillations in the circuit, the capacitor charge and the current in the coil simultaneously take maximum values.

–G. If a resistor is connected in series with the coil,
then the oscillations in the circuit will decay more slowly.

3. The transformer raises the voltage from 120 V to 36 kV. Choose the correct statement.

–A. The number of turns in the secondary is less than in the primary.

–B. The current power in the secondary winding is greater than the power consumed by the transformer from the network.

+IN. The operating current in the secondary is less than in the primary.

–G. EMF of induction in each of the turns secondary winding more than the EMF induction in each of the turns of the primary winding.

4. A closed fixed conducting circuit is in a constant uniform magnetic field directed along the normal to the plane of the circuit. Note which of the following four statements are correct and which are incorrect.

–A. The EMF of induction in the circuit is the greater, the greater the induction of the magnetic field.

+B. If the magnetic field changes, a vortex electric field will arise.

–IN. If the circuit is moved forward, an induction current will arise in it.

+G. If the plane of the circuit is rotated, an induction current will appear in the circuit.

5. To obtain free electromagnetic oscillations, a charged capacitor with a capacity of 1 μF was connected to a coil with an inductance of 10 mH. Note which of the following four statements are correct and which are incorrect.

+A. The vibration amplitude depends on the initial charge of the capacitor.

–B. The period of oscillation in the circuit depends on the initial charge of the capacitor.

–IN. The oscillation frequency in the circuit is less than 800 Hz.

–G. The oscillation period in the circuit is more than 1 ms.

6. A voltmeter connected to an alternating current circuit with a frequency of 50 Hz in parallel with a coil with an inductance of 0.2 H shows 220 V. Note which of the following four statements are correct and which are incorrect.

–A. The voltage amplitude is greater than 400 V.

+B. The effective voltage value is 220 V.

+IN. The effective value of the current in the coil is less than 4 A.

+G. The effective value of the current in the coil is more than 3 A.

8. The figure shows a graph of the voltage change across the capacitor with free oscillations in the oscillatory circuit. The loop inductance is 4 mH. Note which of the following four statements are correct and which are incorrect.

+A. The amplitude value of the voltage across the capacitor is more than 10 V.

+B. The capacitance of the circuit capacitor is greater than 500 pF.

–IN. The voltage across the capacitor changes according to the law

.

+G. The maximum capacitor charge is less than 9 nC.

9. In a coil of 500 turns, a constant induction EMF of 2 kV was excited for 10 ms. Note which of the following four statements are correct and which are incorrect.

+A. The magnetic flux through each turn has changed more than
than 5 mVb.

–B. The magnetic flux through each turn has changed less
than 8 mVb.

+IN. For the induction EMF to increase by 5 times, the rate of change of the magnetic flux must also be increased by 5 times.

–G. The induction EMF in each turn is more than 5 V.

10 ... A coil with an inductance of 20 mH, connected to the battery, has a current of 0.5 A. Note which of the following four statements are correct and which are incorrect.

–A. The EMF of self-induction in the coil is 10 mV.

–B. If the current in the coil is doubled, the magnetic field energy of the coil will also double.

+IN. The magnetic flux through the coil is 10 mWb.

+G. If the coil is disconnected from the current source and short-circuited, an amount of heat of 2.5 mJ will be released in it.

11. The neon lamp is connected to a 220 V, 50 Hz alternating voltage network. Assuming that the lamp both lights up and goes out at 156 volts, note which of the following four statements are correct and which are incorrect.

–A. The lamp flash frequency is 50 Hz.

–B. The lamp is on for more than 2/3 of the period.

–IN. The lamp is on for more than 3/4 of the period.

–G. Each lamp flash lasts less than 2ms.

12. In an oscillatory circuit with a capacitor of 1 μF, resonance is observed at a frequency of 400 Hz. When another capacitor was connected in parallel to the capacitor, the resonant frequency decreased to 200 Hz. Note which of the following four statements are correct and which are incorrect.

+A. The loop inductance is less than 300 mH.

–B. After connecting the second capacitor, the total loop capacitance decreased.

+IN. The capacity of the second capacitor is 3 μF.

+G. At resonance, the capacitive and inductive resistance of the circuit are the same.

Option 4

1. An induction current is generated in a stationary wire frame in a magnetic field. Choose the correct statement.

–A. The current strength is directly proportional to the frame resistance.

–B. The more slowly the magnetic flux through the frame changes, the greater the current.

–IN. The current is maximum when the magnetic flux through the frame
does not change.

+G. If the plane of the frame is parallel to the lines of induction of the magnetic field, the magnetic flux through the frame is zero.

2. The oscillating circuit consists of a capacitor and an inductor. Choose the correct statement.

–A. The energy of a charged capacitor is periodically converted into internal energy during oscillations.

–B. If there are free oscillations in the circuit, then their amplitude increases with time.

+IN. Free damped oscillations can occur in the circuit.

–G. The signs of the charges of the capacitor plates do not change during oscillations.

3. The core of the transformer is not one piece, it is assembled from separate steel plates. Choose the correct statement.

–A. This is done to reduce steel consumption.

+B. This is done to reduce energy losses due to eddy currents in the core.

–IN. There is good electrical contact between the plates.

–G. The transformer core can be made of copper.

4. Note which of the following four statements about self-induction are correct and which are incorrect.

–A. The greater the inductance of a circuit, the less magnetic flux is created by the current flowing in this circuit.

+B. EMF of self-induction in a closed loop is directly proportional to the rate of change in the current in this loop.

–IN. EMF of self-induction always leads to an increase in the current in the circuit.

–G. The self-induction EMF is maximum when the current in the circuit reaches its maximum value.

5. The oscillating circuit consists of a 2.2 µF capacitor and a 0.5 mH coil. Note which of the following four statements are correct and which are incorrect.

–A. If you increase the capacitance of the capacitor, the frequency of free oscillations in the circuit will also increase.

+B. The natural frequency of the loop is less than 5 kHz.

–IN. The natural frequency of the loop is less than 3 kHz.

+G. If the inductance of the coil is reduced by 4 times, the frequency of free oscillations in the circuit will increase by 2 times.

6. An ammeter in series with a 150 ohm resistor in the AC circuit shows 600 mA. Note which of the following four statements are correct and which are incorrect.

–A. The amplitude value of the current in the circuit is greater than 1 A.

–B. If you connect a voltmeter in parallel with a resistor, the voltmeter will show more than 100 V.

+IN. The current power in the resistor is more than 40 W.

+G. The current power in the resistor is more than 50 W.

8. The oscillating circuit consists of a 0.2 µF capacitor and a coil with an inductance of 100 µH. The capacitor was initially charged to a voltage of 40 V. Note which of the following four statements are correct and which are incorrect.

–A. The period of free oscillations in the circuit is less than 20 μs.

+B. Phase shift between voltage fluctuations on a capacitor
and the current strength is a quarter of the period.

+IN. The maximum current in the circuit is greater than 1.2 A.

+G. The capacitor charge exceeds 5 μC at some moments.

9. The figure shows a graph of the time dependence of the EMF of induction in a wire loop rotating in a uniform magnetic field. Note which of the following four statements are correct and which are incorrect.

+A. The amplitude value of the EMF is 8 V.

+B. The variable EMF frequency is more than 45 Hz.

–IN. EMF changes according to the law \u003d 8 cos 100  t.

–G. If the area of \u200b\u200bthe loop is 10 dm 2, then the magnetic field induction is greater than 0.5 T.

10. A closed wire 4 m long was given the shape of a square and placed horizontally in a vertical magnetic field with a magnetic induction of 50 μT. The wire resistance is 2 ohms. Note which of the following four statements are correct and which are incorrect.

–A. The magnetic flux through the circuit is 200 μWb.

–B. When the external field is turned off, a charge of 50 μC will pass through the wire.

–IN. If the wire is shaped into a circle, the magnetic flux through the circuit will decrease.

–G. The induction current in the loop is independent of the loop resistance.

11. A 10 μF capacitor was charged to a voltage of 400 V and connected to an inductor. Due to the presence of active resistance in the circuit, the amplitude of the oscillations decreases by 1% over the period. Note which of the following four statements are correct and which are incorrect.

–A. The oscillations in the circuit are harmonic.

+B. The vibration energy decreases by more than 1.5% over the period.

+IN. During the time of complete damping of oscillations in the circuit, 0.8 J of heat will be released.

–G. If the active resistance of the circuit is increased by 3 times, the oscillation amplitude will decrease by more than 7% over a period.

12. A capacitor is connected in series to the AC voltage network variable capacity and a coreless inductor. By changing the capacitance of the capacitor, we achieved the maximum value of the current in the circuit. After that, the core was inserted into the coil. Note which of the following four statements are correct and which are incorrect.

+A. If you slightly increase the capacitance of the capacitor, the current in the circuit will decrease.

+B. The current in the circuit after the insertion of the core has decreased.

+IN. If the core has increased the inductance of the coil by 20 times, then to obtain the maximum possible current in the circuit, it is necessary to reduce the capacitance of the capacitor by 20 times.

–G. After pushing in the core, the capacitance of the circuit became greater than the inductive reactance.

Electromagnetic induction. Lenz's rule.

The purpose of the lesson: to create conditions for understanding and comprehending the essence of the Lenz rule.

Educational:

Find out how the induction current is directed in the circuit;

formulate Lenz's rule;

demonstrate experimentally and explain the phenomenon of self-induction;

check the assimilation of the studied material

Developing:

development of logical thinking to explain the results of experiments;

development of the intellectual skills of students (observe, apply previously acquired knowledge in a new situation, analyze, draw conclusions);

Educational:

to form a cognitive interest in the study of a physical phenomenon, to foster a culture of social work skills.)

Lesson type: presentation of new material

During the classes

Organizing time.

Today, in the lesson, we will get acquainted with EMP. What stands for electromagnetic induction.

The lesson begins by checking the material learned.

Verificationtest: (Attachment 1)

Motivational stage

Is it possible for a current to flow in a conductor without a current source?

Experience: insertion (removal) of a strip magnet from a closed loop connected to a galvanometer.

Problem: Where did the closed loop current come from?

In case of difficulty, students can be given several prompting questions:

what is the outline? (Answer: closed loop)

what exists around the strip magnet? (answer: there is a magnetic field around the magnet)?

what appears when a magnet is brought into the circuit (taken out)? (Answer: a closed loop permeates the magnetic flux)

what happens to the magnetic flux when a magnet is introduced (removed) into a closed loop? (answer: magnetic flux changes)

Conclusion: The reason for the occurrence of electric current in a closed loop - change in the magnetic flux penetrating the closed loop.

This phenomenon was first discovered by Michael Faraday in 1820. It was called the phenomenon of electromagnetic induction. (Student message about Faraday ..)

Teacher: Electromagnetic induction - a physical phenomenon consisting in the appearance of a vortex electric field, which causes an electric current in a closed circuit when the flux of magnetic induction changes through the surface bounded by this circuit. The current arising in a closed loop is called induction.

Methods for obtaining induction current:

1. moving the magnet and coil relative to each other;
2. moving one coil relative to another;
3. change in current strength in one of the coils;
4. closing and opening the circuit;
5. moving the core;

Experience: closing (opening) the key

The cause of the current: a change in current strength in one circuit leads to a change in magnetic induction.

Experience moving the rheostat engine.

The cause of the current: a change in resistance in the first circuit leads to a change in current strength, and, accordingly, a change in magnetic induction

Teacher: What determines the magnitude and direction of the induction current?

Experience: insertion (removal) of the magnet, first by the north pole, then by the south pole.

Conclusion: The direction of the current depends on the direction of the magnetic field and the direction of movement of the magnet.

Experience: introduction (removal) of a magnet into a closed loop, first with one magnet, then with two magnets

Conclusion: the magnitude of the current depends on the magnitude of the magnetic induction

Experience: insert the magnet slowly at first, then quickly.

Conclusion: The current value depends on the magnet insertion speed.

Interaction of induction current with a magnet. If the magnet is brought closer to the coil, then an induction current appears in it in such a direction that the magnet is necessarily repelled. Positive work must be done to bring the magnet and coil closer together. The coil becomes similar to a magnet with the pole of the same name facing an approaching magnet. The poles of the same name repel.

When the magnet is removed, on the contrary, a current is generated in the coil in such a direction that a force attracting the magnet appears.

What is the difference between the two experiments: the approach of the magnet to the coil and its removal? In the first case, the number of lines of magnetic induction piercing the turns of the coil, or, which is the same, the magnetic flux, increases (Fig. 2.5, a), and in the second case, decreases (Fig. 2.5, b). Moreover, in the first case, the lines of induction of the magnetic field created by the induction current that has arisen in the coil leave the upper end of the coil, since the coil repels the magnet, and in the second case, on the contrary, enter this end. These lines of magnetic induction in Figure 2.5 are shown in black. In case a, a coil with a current is similar to a magnet, the north pole of which is on top, and in case b - below.

This rule can be confirmed by experience. In the installation shown in the figure

At the ends of the rod, which can rotate freely around the vertical axis, two conductive aluminum rings... One of them has a slit. If you bring the magnet to the ring without a cut, then an induction current will arise in it and it will be directed so that this ring will repel from the magnet and the rod will turn. If you remove the magnet from the ring, then, on the contrary, it will be attracted to the magnet. The magnet does not interact with the cut ring, since the cut prevents the induction current in the ring. The magnet pushes or attracts the coil, it depends on the direction of the induction current in it. Therefore, the law of conservation of energy makes it possible to formulate a rule that determines the direction of the induction current.

Lenz's rule. Now we have come to the main point: with an increase in the magnetic flux through the turns of the coil, the induction current has such a direction that the magnetic field created by it prevents the increase in the magnetic flux through the turns of the coil. After all, the induction lines of this field are directed against the induction lines of the field, a change in which generates an electric current. If the magnetic flux through the coil weakens, then the induction
the current creates a magnetic field with induction, which increases the magnetic flux through the turns of the coil.

This is the essence of the general rule for determining the direction of the induction t Teacher: To determine the direction of the induction current in a closed loop, it is used lenz rule :

The induction current has such a direction that the magnetic flux created by it through the surface bounded by the contour prevents the change in the magnetic flux that caused this current.

The direction of the induction current depends on:
1) from the increase or decrease of the magnetic flux penetrating the circuit;
2) on the direction of the magnetic induction vector relative to the contour

Induction current direction -

Straight conductor:

The direction of the induction current is determined by the right hand rule:

If you put your right hand so that the magnetic induction vector enters the palm, the thumb set aside by 90 degrees indicates the direction of the velocity vector, then the straightened 4 fingers will show the direction of the induction current in the conductor.

Closed loop:

The direction of the induction current in a closed loop is determined by the Lenz rule.

an eye that is applicable in all cases.

Lenz's rule

The induction current arising in a closed loop with its magnetic field counteracts the change in the magnetic flux by which it is caused.

Application of Lenz's rule
1. show the direction of the vector B of the external magnetic field;
2. determine whether the magnetic flux through the circuit increases or decreases;
3. show the direction of the vector Вi of the magnetic field of the induction current (with a decrease in the magnetic flux of the vector B of the external m, the fields and Вi of the magnetic field of the induction current should be directed in the same way, and with an increase in the magnetic flux, B and Bi should be directed oppositely);
4. Determine the direction of the induction current in the circuit according to the gimbal's rule.

6. Homework.(on cards) A closed circuit with a light bulb is introduced into the steel core of a transformer connected to a voltage of 220V (RNSH). Why does the light come on at the same time?

Teacher: The phenomenon of electromagnetic induction has found wide application in technology: transformers, magnetic levitation trains, metal detectors (metal detectors), recording and reading information on magnetic media

Lesson summary.1) What is the EMP phenomenon?

2) Let us recall the experiments that allow observing this phenomenon.

3) Who discovered the EMP phenomenon?

4) What did we determine using Lenz's rule?

5) Application of EMP.

Verification test: (Attachment 1)

How the two interact parallel conductorif the electric current flows in them in one direction:

A) the force of interaction is zero;

B) conductors are attracted;

C) the conductors are repelled;

D) conductors turn in one direction.

When does a magnetic field arise around a moving electron?

1) the electron moves uniformly and rectilinearly;

2) the electron moves uniformly;

3) the electron moves uniformly accelerated.

D) there is no such case.

3. What is the physical value of 1 Tesla?

A) magnetic flux;

B) magnetic induction;

B) inductance.

4. The flux of magnetic induction through a surface of area S is determined by the formula:

B) BStg a;

D) BScos a.

5. The closed loop with area S was turned by 60? in a uniform magnetic field with induction B. In this case, the magnetic flux penetrating this circuit:

A) increased by 2 times;

B) decreased by 2 times;

C) has not changed.

6. In a closed loop with an area S, located in a uniform magnetic field, the current was increased 3 times. The magnetic flux penetrating this circuit, while:

A) decreased by 3 times;

B) increased by 3 times;

C) has not changed.

7. In a uniform magnetic field with an induction of 1 T, two closed circuits with an area of \u200b\u200b10 and 20 cm 2 are located perpendicular to it, respectively. Magnetic flux permeating the first circuit versus magnetic flux permeating the second circuit: the charge should be placed in the center ... induction current depends on resistance contour. Direction induction current determined by the rule Lenz. Induction current always directed So...

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... as has already been shown, should summarize the experience of word use and try formulate general the rule ... A task was to to figure out, what are the values \u200b\u200band direction ... economic, educational and... circuit ... chain induction coils ...