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The Lenz's law for electromagnetic induction

Induction current generates its own magnetic field. The relationship between the direction of the induction current in the circuit and the inducing magnetic field was installed Lenz.

In the experience, depicted in figure. 23.3, induction current in the solenoid creates a magnetic field, the poles of which are indicated in the bore of the solenoid. Tracing the interaction between the magnetic poles of the solenoid and magnet in all four cases, shown in the figure, and comparing it with the direction of movement of the magnet, you can see, the interaction between the poles always prevents movement of the magnet. Lenz was able to generalize this pattern for all cases of electromagnetic induction. He found a link called the law (rule) For Lenz law of electromagnetic induction: e. d. with. induction creates in the closed circuit of this induction current, which its magnetic field prevents reason, calling the appearance of this e. d. with.

Using Lenz's law to determine the direction of the induction current, you should do the following:

  • to find the cause, creating an induction current;
  • considering, what induction current counteracts this reason, find the direction of its magnetic field;
  • to determine the direction of induced current in the direction of its magnetic field.

Here is an example. The reason, causing the appearance of the induction current in the secondary coil by opening the circuit of the primary coil (rice. 23.5), is the disappearance of the magnetic field of primary coil. Preventing this disappearance, the induction current in the secondary coil must generate a magnetic field of the same direction, as the field of the primary coil. Therefore, the direction of the induction current in the secondary coil will be the same as the direction of the current, which flowed in the primary coil before opening. (Show, what with the closure of the circuit of the primary coil to the secondary of a current reverse direction.)

From Lenz's law can be set, the energy of the induction current in the conductor is obtained from the energy, which is expended to overcome the counteracting magnetic field of the induction current. For example, if open circuit coil, depicted in figure. 23.3, and count work, needed, to paste and remove the magnet a certain number of times, and then to repeat this experience with closed circuit, in the second case, the work will be considerably more, than in the first. This is due to the, in the first case, the self-magnetic field around the coil no, as there is no current, and in the second case the field is. Extra work in the second case is the resistance of this field and is equal to the energy of the induction current in the coil. It is easy to see, that the phenomenon of electromagnetic induction to transform mechanical energy into electrical energy, and also to transfer electric energy from one circuit to another.

When the induction current arises due to any mechanical movement, the electric energy was produced by mechanical. This conversion of energy occurs in induction generators, installed in power plants. When induction current is generated in the absence of mechanical movement, the electrical energy passes from one circuit to another. This transfer of energy occurs in transformers.

The phenomenon of electromagnetic induction explain diamagnetic effect. When a substance enters the magnetic field, each orbiting electron begins to act Lorentz force, which increases or decreases (depending on the direction of rotation of the electron) centripetal force, acting on the electron. This leads to a change of the orbit and orbital frequency of the electron, that amounts to a reduction or an increase in circular current, corresponding to the motion of an electron in an orbit, and it turns out, that circular electron currents are amplified, if the magnetic field directed against the external field, and decrease, if they are directed on the field.

Thus, if in the absence of external elds of circular currents of electrons in the molecule of a diamagnetic substance balance each other, and the molecule has no magnetic moment, then in an external field this balance is disturbed and there is a resultant magnetic moment of the molecule, directed against the external field. This result, generally speaking, directly follows from the Lenz's law: change circular currents in the molecule is the induction current, and its magnetic field must be directed against the external field вызвави1вго it.

The diamagnetic effect that occurs in all substances, but if molecules have intrinsic magnetic moments, which are oriented in the direction of the external magnetic field and amplify it, the diamagnetic effect is blocked a stronger paramagnetic effect and the substance is paramagnetic.

Strong diamagnetic effect is observed when superconductivity. When the superconductor enters the magnetic field, in it, like in normal Windows Explorer, induced induction currents, but, in contrast to the induction of molecular currents, they are formed by free electrons. In these superconductor induction currents do not encounter any resistance and circulating, while there is an external magnetic field, counteracting to its penetration inside the superconductor. Superconductors, like all the diamagnetic, are pushed out of the magnetic field.

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