very important practical significance is a special case of the phenomenon of electromagnetic induction, called self-induction.Thus, when the induction coil forms a current that occurs simultaneously with the flux and which increases with increasing current.With the change in magnetic flux coil induces an electromotive force (EMF), the magnitude of which is proportional to the rate of change of magnetic flux.
Since in this case the conductor induces an electromotive force in itself, this phenomenon is called self-induction.The phenomenon of self-induction in electrical circuits is sometimes compared with the manifestation of inertia in mechanics.
electromotive force induced in the induction coil under the influence of changes of its own magnetic flux is called self-induction electromotive force.
According to Lenz's law, during the whole growth of the magnetic flux permeated the turns of the coil, self-induction EMF in the coil is directed against the electromotive force source, is included in this circuit, and prevents the growth of the current in the coil circuit.
When the current in the coil reaches a constant value, the magnetic flux change stops and the self-induction electromotive force in the coil becomes zero.
When the self-induction, as in any process of electromagnetic induction, the induced electromotive force is proportional to the speed at which the magnetic flux is coupled with the circuit through which current flows, is changed.The magnitude of the magnetic flux in the absence of iron in the coil is proportional to the speed with which changes the current (ΔI / Δt), creating the flow.
Thus, the magnitude of the self-induction electromotive force occurring in a conductor is proportional to the rate at which current changes therein.
If you take the wires of different shapes, it turns out that having the same rate of change of current, electromotive force of self-induction, resulting in them will be different.
Thus, if we take the coil and then to stretch in one revolution, then at the same rate at which the current change occurs, the self-induction EMF coils will be higher.This is due to the fact that each power line prinizyvaya coil turns, it is engaged with a larger number of times than a single loop.
variables characterizing the connection between the rate at which the current changes in a chain, and there is thus self-induction EMF - circuit inductance.
denote the inductance of the coil by the letter L;then the dependence of the electromotive force of self-induction of the speed with which a change in current can be expressed by the following formula:
E = - L (ΔI / Δt)
units.L = (ed.E ˖ units. T) / (ed.I)
Assuming that in this formula Δt = 1 s, ΔI = 1A and E = 1 volt, we obtain:
units.L = 1 (in ˖ s / a)
This unit is called the Henry (H).
1 TR = 1 (in ˖ s / a)
So Henry - is inductance of the coil in which the current change of 1 ampere per second, excites the self-induction electromotive force equal to 1 volt.
for measuring small inductances used thousandths of Henry - MH (mH) or millionths of a henry - microHenry (uH).
In addition, frequently used, and other unit - centimeter inductance, with 1 cm = 1000 uH inductance.
1 TR = 1000 uH mH = 1000000 = 1000000000 see
inductance coil is dependent on its number of turns, shapes and sizes.The greater the number of turns in the coil self-inductance, the greater its inductance.
Also, the inductance, the inductance increases considerably when introducing it into the core of iron or any other magnetic material.
have a large inductive coil magnets have generators and motors, open circuit at the time when the rate of change of the electric current (ΔI / Δt) is very high in these windings can be a great self-induction EMF, which, if not avoided, will result inbreakdown of the winding insulation.