Law of electromagnetic induction abstract. The phenomenon of electromagnetic induction. Magnetic flux. Lenz's rule. Law of Electromagnetic Induction

The phenomenon of electromagnetic induction was discovered by the outstanding English physicist M. Faraday in 1831. It consists in the occurrence of an electric current in a closed conducting circuit when the magnetic flux penetrating the circuit changes over time.
The magnetic flux Φ through the area S of the circuit is the quantity

Φ = B S cos α,

Where B is the magnitude of the magnetic induction vector, α is the angle between the vector and the normal to the contour plane (Fig. 4.20.1).

Figure 4.20.1.
Magnetic flux through a closed loop. The normal direction and the selected positive direction of the contour traversal are related by the right gimlet rule.
The definition of magnetic flux is easy to generalize to the case of a non-uniform magnetic field and a non-planar circuit. The SI unit of magnetic flux is called the weber (Wb). A magnetic flux equal to 1 Wb is created by a magnetic field with an induction of 1 T, penetrating in the normal direction a flat contour with an area of ​​1 m2:

1 Wb = 1 T · 1 m2.

Faraday experimentally established that when the magnetic flux changes in a conducting circuit, an induced emf Eind arises, equal to the rate of change of the magnetic flux through the surface bounded by the circuit, taken with a minus sign:

Experience shows that the induction current excited in a closed loop when the magnetic flux changes is always directed in such a way that the magnetic field it creates prevents the change in the magnetic flux that causes the induction current. This statement is called Lenz's rule (1833).
Rice. 4.20.2 illustrates Lenz’s rule using the example of a stationary conducting circuit that is in a uniform magnetic field, the induction modulus of which increases with time.

Figure 4.20.2.
Illustration of Lenz's rule. In this example, a ind< 0. Индукционный ток Iинд течет навстречу выбранному положительному направлению обхода контура.
Lenz's rule reflects the experimental fact that ind and always have opposite signs (the minus sign in Faraday's formula). Lenz's rule has a deep physical meaning - it expresses the law of conservation of energy.
A change in the magnetic flux penetrating a closed circuit can occur for two reasons.
1. The magnetic flux changes due to the movement of the circuit or its parts in a time-constant magnetic field. This is the case when conductors, and with them free charge carriers, move in a magnetic field. The occurrence of induced emf is explained by the action of the Lorentz force on free charges in moving conductors. The Lorentz force plays the role of an external force in this case.
Let us consider, as an example, the occurrence of an induced emf in a rectangular circuit placed in a uniform magnetic field perpendicular to the plane of the circuit. Let one of the sides of a contour of length l slide with speed along the other two sides (Fig. 4.20.3).

Figure 4.20.3.
The occurrence of induced emf in a moving conductor. The component of the Lorentz force acting on a free electron is indicated.
The Lorentz force acts on the free charges in this section of the circuit. One of the components of this force, associated with the transfer speed of charges, is directed along the conductor. This component is shown in Fig. 4.20.3. She plays the role of an outside force. Its module is equal

The work done by the force FL on the path l is equal to

A = FL · l = eυBl.

According to the definition of EMF

In other stationary parts of the circuit, the external force is zero. The ratio for ind can be given the usual form. Over time Δt, the contour area changes by ΔS = lυΔt. The change in magnetic flux during this time is equal to ΔΦ = BlυΔt. Hence,

In order to establish the sign in the formula connecting ind and it is necessary to select the normal direction and the positive direction of traversing the contour that are consistent with each other according to the right gimlet rule, as is done in Fig. 4.20.1 and 4.20.2. If this is done, then it is easy to arrive at Faraday's formula.
If the resistance of the entire circuit is equal to R, then an induction current equal to Iind = ind/R will flow through it. During the time Δt, Joule heat will be released at the resistance R (see § 4.11)

The question arises: where does this energy come from, since the Lorentz force does no work! This paradox arose because we took into account the work of only one component of the Lorentz force. When an induction current flows through a conductor located in a magnetic field, another component of the Lorentz force, associated with the relative speed of movement of the charges along the conductor, acts on the free charges. This component is responsible for the appearance of the Ampere force. For the case shown in Fig. 4.20.3, the ampere force modulus is FA = IBl. Ampere's force is directed towards the movement of the conductor; therefore it does negative mechanical work. During the time Δt this work Amech is equal to

A conductor moving in a magnetic field through which an induced current flows experiences magnetic braking. The total work done by the Lorentz force is zero. Joule heat in the circuit is released either due to the work of an external force, which maintains the speed of the conductor unchanged, or due to a decrease in the kinetic energy of the conductor.
2. The second reason for the change in the magnetic flux penetrating the circuit is the change in time of the magnetic field when the circuit is stationary. In this case, the occurrence of induced emf can no longer be explained by the action of the Lorentz force. Electrons in a stationary conductor can only be driven by an electric field. This electric field is generated by a time-varying magnetic field. The work of this field when moving a single positive charge along a closed circuit is equal to the induced emf in a stationary conductor. Therefore, the electric field generated by a changing magnetic field is not potential. It is called the vortex electric field. The concept of a vortex electric field was introduced into physics by the great English physicist J. Maxwell (1861).
The phenomenon of electromagnetic induction in stationary conductors, which occurs when the surrounding magnetic field changes, is also described by Faraday's formula. Thus, the phenomena of induction in moving and stationary conductors proceed in the same way, but the physical cause of the occurrence of the induced current turns out to be different in these two cases: in the case of moving conductors, the induction emf is due to the Lorentz force; in the case of stationary conductors, the induced emf is a consequence of the action on free charges of the vortex electric field that occurs when the magnetic field changes.

The purpose of the lesson: formulate a concept about induction current, develop the ability to determine the direction of induction current using Lenz’s rule.

During the classes

Checking homework

- How was the phenomenon of electromagnetic induction discovered by M. Faraday?

Show Faraday's experiments on detecting electromagnetic induction.

Draw conclusions and explain what kind of phenomenon this is - electromagnetic induction?

What determines the magnitude of the induction current in the circuit?

What is magnetic flux?

Make a drawing on the board and derive a formula for calculating magnetic flux.

Learning new material

If a galvanometer is connected to a coil in which an induced current can occur, you will notice that the arrow deviates in different directions depending on whether the magnet approaches or moves away from the coil; The deviation of the galvanometer needle also depends on the pole of the magnet.

This means that the induction current changes its direction. A coil with current flowing is like a magnet with a south and north pole. You can predict when the coil will attract the magnet and when it will repel it.

Interaction of a magnet with an induction current.

In order to bring the magnet and the coil together, work must be done. Since when a magnet approaches a coil, a pole of the same name appears at the nearest end of the coil, the magnet and the coil repel each other. If they were attracted, then the law of conservation of energy would be violated. Prove this position. Confirm the conclusion using the device shown in the figure. You can clearly see how when a magnet approaches a closed ring, it will be repelled from the magnet. When the magnet is removed from the ring, it begins to be attracted to the magnet.

Nothing happens to the cut ring, since no induced current is created in it.

Whether a magnet repels or attracts a coil depends on the direction of the induction current.

Based on the law of conservation of energy, we obtained a rule that allows us to determine the direction of the induction current.

In the first figure we see that as the magnet approaches the coil, the magnetic flux penetrating the turns of the coil increases, and in the second case it decreases.

In the first picture, the newly created induction lines come out of the upper end of the coil (the coil repels the magnet), in the second picture it is the other way around.

Lenz's rule. The induced current arising in a closed circuit with its magnetic field counteracts the change in the magnetic flux that causes it.

Consolidation of the studied material.

How to determine the direction of the induction current?

What will happen in the ring when a magnet is inserted into it, if the ring is made of: a) not a conductor;

B) conductor; c) superconductor?

Electromagnetic induction- this is a phenomenon that consists in the occurrence of an electric current in a closed conductor as a result of a change in the magnetic field in which it is located. This phenomenon was discovered by the English physicist M. Faraday in 1831. Its essence can be explained by several simple experiments.

Described in Faraday's experiments principle of obtaining alternating current used in induction generators that generate electrical energy in thermal or hydroelectric power plants. The resistance to rotation of the generator rotor, which arises when the induction current interacts with the magnetic field, is overcome by the operation of a steam or hydraulic turbine that rotates the rotor. Such generators convert mechanical energy into electrical energy .

Eddy currents or Foucault currents

If a massive conductor is placed in an alternating magnetic field, then in this conductor, due to the phenomenon of electromagnetic induction, eddy induced currents arise, called Foucault's currents.

Eddy currents also arise when a massive conductor moves in a constant, but spatially inhomogeneous magnetic field. Foucault currents have such a direction that the force acting on them in a magnetic field inhibits the movement of the conductor. A pendulum in the form of a solid metal plate made of non-magnetic material, oscillating between the poles of an electromagnet, stops abruptly when the magnetic field is turned on.

In many cases, the heating caused by Foucault currents turns out to be harmful and must be dealt with. Transformer cores and electric motor rotors are made from separate iron plates, separated by layers of insulator that prevent the development of large induction currents, and the plates themselves are made from alloys with high resistivity.

Electromagnetic field

The electric field created by stationary charges is static and acts on the charges. Direct current causes the appearance of a time-constant magnetic field acting on moving charges and currents. Electric and magnetic fields exist in this case independently of each other.

Phenomenon electromagnetic induction demonstrates the interaction of these fields observed in substances that have free charges, i.e., in conductors. An alternating magnetic field creates an alternating electric field, which, acting on free charges, creates an electric current. This current, being alternating, in turn generates an alternating magnetic field, which creates an electric field in the same conductor, etc.

The set of alternating electric and alternating magnetic fields that generate each other is called electromagnetic field. It can exist in a medium where there are no free charges, and propagates in space in the form of an electromagnetic wave.

Classical electrodynamics- one of the highest achievements of the human mind. She had a huge influence on the subsequent development of human civilization by predicting the existence of electromagnetic waves. This subsequently led to the creation of radio, television, telecommunication systems, satellite navigation, as well as computers, industrial and household robots and other attributes of modern life.

cornerstone Maxwell's theories It was stated that the source of a magnetic field can only be an alternating electric field, just as the source of an electric field that creates an induction current in a conductor is an alternating magnetic field. The presence of a conductor is not necessary - an electric field also arises in empty space. The alternating electric field lines, similar to the magnetic field lines, are closed. The electric and magnetic fields of an electromagnetic wave are equal.

Electromagnetic induction in diagrams and tables

In this lesson, the topic of which is: “Lenz’s rule. The Law of Electromagnetic Induction,” we learn a general rule that allows us to determine the direction of the induced current in a circuit, established in 1833 by E.X. Lenz. We will also consider the experiment with aluminum rings, which clearly demonstrates this rule, and formulate the law of electromagnetic induction

By bringing the magnet closer to or moving away from the solid ring, we change the magnetic flux that penetrates the area of ​​the ring. According to the theory of the phenomenon of electromagnetic induction, an inductive electric current should arise in the ring. From Ampere's experiments it is known that where the current passes, a magnetic field arises. Consequently, the closed ring begins to behave like a magnet. That is, there is an interaction between two magnets (a permanent magnet that we move, and a closed circuit with current).

Since the system did not react to the approach of the magnet to the ring with the cut, we can conclude that the induced current does not arise in the open circuit.

Reasons for repulsion or attraction of a ring to a magnet

1. When a magnet approaches

As the pole of the magnet approaches, the ring is repelled from it. That is, it behaves like a magnet, which on our side has the same pole as the approaching magnet. If we bring the north pole of the magnet closer, then the magnetic induction vector of the ring with the induced current is directed in the opposite direction relative to the magnetic induction vector of the north pole of the magnet (see Fig. 2).

Rice. 2. Approaching the magnet to the ring

2. When removing the magnet from the ring

When the magnet is removed, the ring is pulled behind it. Consequently, on the side of the receding magnet, an opposite pole is formed at the ring. The magnetic induction vector of the current-carrying ring is directed in the same direction as the magnetic induction vector of the receding magnet (see Fig. 3).

Rice. 3. Removing the magnet from the ring

From this experiment we can conclude that when the magnet moves, the ring also behaves like a magnet, the polarity of which depends on whether the magnetic flux penetrating the area of ​​the ring increases or decreases. If the flux increases, then the magnetic induction vectors of the ring and magnet are opposite in direction. If the magnetic flux through the ring decreases with time, then the induction vector of the magnetic field of the ring coincides in direction with the induction vector of the magnet.

The direction of the induced current in the ring can be determined by the right-hand rule. If you point the thumb of your right hand in the direction of the magnetic induction vector, then the four bent fingers will indicate the direction of the current in the ring (see Fig. 4).

Rice. 4. Right hand rule

When the magnetic flux penetrating the circuit changes, an induced current appears in the circuit in such a direction that its magnetic flux compensates for the change in the external magnetic flux.

If the external magnetic flux increases, then the induced current, with its magnetic field, tends to slow down this increase. If the magnetic flux decreases, then the induced current with its magnetic field tends to slow down this decrease.

This feature of electromagnetic induction is expressed by the minus sign in the induced emf formula.

Law of Electromagnetic Induction

When the external magnetic flux penetrating the circuit changes, an induced current appears in the circuit. In this case, the value of the electromotive force is numerically equal to the rate of change of the magnetic flux, taken with the “-” sign.

Lenz's rule is a consequence of the law of conservation of energy in electromagnetic phenomena.

Bibliography

1. Myakishev G.Ya. Physics: Textbook. for 11th grade general education institutions. - M.: Education, 2010.
2. Kasyanov V.A. Physics. 11th grade: Educational. for general education institutions. - M.: Bustard, 2005.
3. Gendenstein L.E., Dick Yu.I., Physics 11. - M.: Mnemosyne.

Homework

1. Questions at the end of paragraph 10 (p. 33) - Myakishev G.Ya. Physics 11 (see list of recommended readings)
2. How is the law of electromagnetic induction formulated?
3. Why is there a “-” sign in the formula for the law of electromagnetic induction?

1. Internet portal Festival.1september.ru ().
2. Internet portal Physics.kgsu.ru ().
3. Internet portal Youtube.com ().

LAW OF ELECTROMAGNETIC INDUCTION. LENZ'S RULE
In 1831, the English physicist M. Faraday discovered the phenomenon of electromagnetic induction in his experiments. Then the Russian scientist E.Kh. studied this phenomenon. Lenz and B. S. Jacobi.
Currently, many devices are based on the phenomenon of electromagnetic induction, for example in a motor or electric current generator, in transformers, radio receivers, and many other devices.
Electromagnetic induction is the phenomenon of the occurrence of current in a closed conductor when a magnetic flux passes through it.
That is, thanks to this phenomenon we can convert mechanical energy into electrical energy. Before the discovery of this phenomenon, people did not know about methods of producing electric current other than electroplating.
When a conductor is exposed to a magnetic field, an emf arises in it, which can be quantitatively expressed through the law of electromagnetic induction.
Law of Electromagnetic Induction
The electromotive force induced in a conducting circuit is equal to the rate of change of the magnetic flux coupling to that circuit.

In a coil that has several turns, the total emf depends on the number of turns n:

The EMF excited in the circuit creates a current. The simplest example of the appearance of current in a conductor is a coil through which a permanent magnet passes. The direction of the induced current can be determined using Lenz's rule.

Lenz's rule
The current induced by a change in the magnetic field passing through the circuit prevents this change with its magnetic field.

In the case when we introduce a magnet into the coil, the magnetic flux in the circuit increases, which means that the magnetic field created by the induced current, according to Lenz’s rule, is directed against the increase in the magnet’s field. To determine the direction of the current, you need to look at the magnet from the north pole. From this position we will screw the gimlet in the direction of the magnetic field of the current, that is, towards the north pole. The current will move in the direction of rotation of the gimlet, that is, clockwise.
In the case when we remove the magnet from the coil, the magnetic flux in the circuit decreases, which means the magnetic field created by the induced current is directed against the decrease in the magnet's field. To determine the direction of the current, you need to unscrew the gimlet; the direction of rotation of the gimlet will indicate the direction of the current in the conductor - counterclockwise.
An electric generator is a device in which non-electrical types of energy (mechanical, chemical, thermal) are converted into electrical energy.
Classification of electromechanical generators
By type of prime mover:
Turbogenerator - an electrical generator driven by a steam turbine or gas turbine engine;
Hydrogenerator - an electric generator driven by a hydraulic turbine;
Diesel generator - an electric generator driven by a diesel engine;
Wind generator - an electric generator that converts the kinetic energy of the wind into electricity;
According to the type of output electric current
Three-phase generator with star windings
With triangle windings included
According to the method of excitation
Excited by permanent magnets
With external excitation
Self-excited
With sequential excitation
With parallel excitation
With mixed excitement
According to the principle of operation, generators can be synchronous or asynchronous.
Asynchronous generators are structurally simple and inexpensive to manufacture, and are more resistant to short circuit currents and overloads. An asynchronous electric generator is ideal for powering active loads: incandescent lamps, electric heaters, electronics, electric burners, etc. But even short-term overload is unacceptable for them, therefore, when connecting electric motors, non-electronic welding machines, power tools and other inductive loads, there is a reserve of power should be at least three times, and preferably four times.
A synchronous generator is perfect for inductive consumers with high starting currents. They are capable of withstanding a fivefold current overload for one second.
Operating principle of the current generator
The generator operates on the basis of Faraday's law of electromagnetic induction - electromotive force (EMF) is induced in a rectangular loop (wire frame) rotating in a uniform magnetic field.
EMF also occurs in a stationary rectangular frame if a magnet is rotated in it.
The simplest generator is a rectangular frame placed between 2 magnets with different poles. In order to remove the voltage from the rotating frame, slip rings are used.

A car generator consists of a housing and two covers with holes for ventilation. The rotor rotates in 2 bearings and is driven by a pulley. At its core, the rotor is an electromagnet consisting of one winding. Current is supplied to it using two copper rings and graphite brushes, which are connected to an electronic relay controller. He is responsible for ensuring that the voltage supplied by the generator is always within the permissible limits of 12 Volts with permissible deviations and does not depend on the pulley rotation speed. The relay regulator can be either built into the generator housing or located outside it.
The stator consists of three copper windings interconnected in a triangle. A rectifier bridge of 6 semiconductor diodes is connected to their connection points, which convert the voltage from AC to DC.
A gasoline electric generator consists of an engine and a current generator driving it directly, which can be either synchronous or asynchronous.
The engine is equipped with systems: starting, fuel injection, cooling, lubrication, speed stabilization. Vibration and noise are absorbed by a muffler, vibration dampers and shock absorbers.
Alternating electric current
Electromagnetic vibrations, like mechanical ones, are of two types: free and forced.
Free electromagnetic oscillations, always damped oscillations. Therefore, in practice they are almost never used. While forced vibrations are used everywhere and everywhere. Every day you and I can observe these fluctuations.
All our apartments are lit using alternating current. Alternating current is nothing more than forced electromagnetic oscillations. The current and voltage will change over time according to the harmonic law. Fluctuations, for example, in voltage can be detected by applying voltage from an outlet to an oscilloscope.
A sine wave will appear on the oscilloscope screen. The frequency of alternating current can be calculated. It will be equal to the frequency of electromagnetic oscillations. The standard frequency for industrial alternating current is assumed to be 50 Hz. That is, in 1 second the direction of the current in the socket changes 50 times. US industrial networks use a frequency of 60 Hz.
A change in voltage at the ends of the circuit will cause a change in the current strength in the oscillatory circuit circuit. It should still be understood that the change in the electric field in the entire circuit does not occur instantly.
But since this time is significantly less than the period of voltage oscillation at the ends of the circuit, it is usually believed that the electric field in the circuit immediately changes as the voltage at the ends of the circuit changes.
The alternating voltage in the outlet is created by generators in power plants. The simplest generator can be considered a wire frame that rotates in a uniform magnetic field.
The magnetic flux penetrating the circuit will constantly change and will be proportional to the cosine of the angle between the magnetic induction vector and the normal to the frame. If the frame rotates uniformly, the angle will be proportional to time.
Consequently, the magnetic flux will change according to the harmonic law:
Ф = B*S*cos(ω*t)
The rate of change of magnetic flux, taken with the opposite sign, according to the EMR law, will be equal to the induced emf.
Ei = -Ф’ = Em*sin(ω*t).
If an oscillatory circuit is connected to the frame, the angular speed of rotation of the frame will determine the frequency of voltage oscillations in different sections of the circuit and the current strength. In what follows, we will consider only forced electromagnetic oscillations.
They are described by the following formulas:
u = Um*sin(ω*t),
u = Um*cos(ω*t)
Here Um is the amplitude of voltage fluctuations. Voltage and current change with the same frequency ω. But voltage fluctuations will not always coincide with current fluctuations, so it is better to use a more general formula:
I = Im*sin(ω*t +φ), where Im is the amplitude of current fluctuations, and φ is the phase shift between current and voltage fluctuations.
AC current and voltage parameters
The magnitude of alternating current, like voltage, constantly changes over time. Quantitative indicators for measurements and calculations use their following parameters:

Period T is the time during which one complete cycle of current change occurs in both directions relative to zero or the average value.
Frequency f is the reciprocal of the period, equal to the number of periods in one second. One period per second is one hertz (1 Hz)
f = 1/T
Cyclic frequency ω - angular frequency equal to the number of periods in 2π seconds.

ω = 2πf = 2π/T
Typically used in sinusoidal current and voltage calculations. Then, within the period, one can not consider frequency and time, but make calculations in radians or degrees. T = 2π = 360°
The initial phase ψ is the value of the angle from zero (ωt = 0) to the beginning of the period. Measured in radians or degrees. Shown in the figure for a blue sinusoidal current graph. The initial phase can be a positive or negative value, respectively to the right or left of zero on the graph.
Instantaneous value - the value of voltage or current measured relative to zero at any selected time t.
i = i(t); u = u(t)
The sequence of all instantaneous values ​​in any time interval can be considered as a function of the change in current or voltage over time. For example, a sinusoidal current or voltage can be expressed by the function:
i = Iampsin(ωt); u = Uampsin(ωt)
Taking into account the initial phase:
i = Iampsin(ωt + ψ); u = Uampsin(ωt + ψ)
Here Iamp and Uamp are the amplitude values ​​of current and voltage.
Amplitude value is the maximum absolute instantaneous value for the period.
Iamp = max|i(t)|; Uamp = max|u(t)|
Can be positive or negative depending on its position relative to zero. Often, instead of the amplitude value, the term current (voltage) amplitude is used - the maximum deviation from the zero value.
D/z
Report on the topic (of the student's choice)
Electricity generation and transmission
Transformer. Transmission of electricity over a distance
Energy saving in everyday lifeFirst experiments in transmitting electricity over a distance Transformer efficiency. Design and operationUse of electricityTurbogenerator. Design and operation
Hydrogenerator. Design and operation
Diesel generator. Design and operation
Wind generator. Design and operation
Problems to solve independently
Faraday's law of EM induction.
1. The magnetic flux inside a coil with a number of turns equal to 400 changed from 0.1 Wb to 0.9 Wb in 0.2 s. Determine the emf induced in the coil.
2. Determine the magnetic flux passing through a rectangular area with sides of 20x40 cm, if it is placed in a uniform magnetic field with an induction of 5 Tesla at an angle of 60° to the lines of magnetic induction of the field.
3. How many turns should the coil have so that when the magnetic flux inside it changes from 0.024 to 0.056 Wb in 0.32 s, an average emf is created in it. 10 V?
Induction emf in moving conductors.
1. Determine the induced emf at the ends of the wings of the An-2 aircraft, having a length of 12.4 m, if the speed of the aircraft in horizontal flight is 180 km/h, and the vertical component of the induction vector of the Earth’s magnetic field is 0.5·10-4 T.
2. Find the induced emf on the wings of a Tu-204 aircraft, having a length of 42 m, flying horizontally at a speed of 850 km/h, if the vertical component of the induction vector of the Earth’s magnetic field is 5·10-5 T.
Self-induced emf
1. A magnetic flux of 0.015 Wb appears in a coil when a current of 5.0 A passes through its turns. How many turns does the coil contain if its inductance is 60 mH?
2. How many times will the inductance of a coil without a core change if the number of turns in it is doubled?
3. What is the e.m.f. self-induction will occur in a coil with an inductance of 68 mH if a current of 3.8 A disappears in it in 0.012 s?
4. Determine the inductance of the coil if, when the current in it is weakened by 2.8 A, an average emf appears in the coil in 62 ms. self-induction 14 V.
5. How long does it take in a coil with an inductance of 240 mH to increase the current from zero to 11.4 A, if an average emf occurs? self-induction 30 V?
Electromagnetic field energy
1. A current of 20 A flows through a coil with an inductance of 0.6 H. What is the energy of the magnetic field of the coil? How will this energy change when the current increases by a factor of 2? 3 times?
2. How much current must be passed through the winding of an inductor with an inductance of 0.5 H so that the field energy is equal to 100 J?
3. The energy of the magnetic field of which coil is greater and by how many times, if the first has the characteristics: I1=10A, L1=20 H, the second: I2=20A, L2=10 H?
4. Determine the energy of the magnetic field of the coil in which, at a current of 7.5 A, the magnetic flux is 2.3·10-3 Wb. The number of turns in the coil is 120.
5. Determine the inductance of the coil if, at a current of 6.2 A, its magnetic field has an energy of 0.32 J.
6. The magnetic field of a coil with an inductance of 95 mH has an energy of 0.19 J. What is the current strength in the coil?