Coil Inductance

Of particular practical importance is one particular case of the phenomenon of electromagnetic induction, called self-induction. So, when the induction coil forms a current, simultaneously with it there is also a magnetic flux, which increases with increasing current. With the change in magnetic flux, the coil induces an electromotive force (EMF), the magnitude of which is proportional to the change in the magnetic flux velocity.

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.

The electromotive force induced in an induction coil under the influence of a change in its own magnetic flux is called the electromotive force of self-induction.

According to Lenz's law, during the entire growth of the magnetic flux that coils the coils, the self-inductance EMF in the coil is directed against the electromotive force of the source included in this circuit and counteracts the current growth in the coil circuit.

When the current in the coil reaches a constant value, the magnetic flux stops the change, and the EMF of self-induction in the coil becomes zero.
In self-induction, as in any electromagnetic induction process, the induced electromotive force is proportional to the rate at which the magnetic flux linked to the circuit through which the current flows varies. The magnitude of the magnetic flux in the absence of iron in the coil is proportional to the rate at which the current (ΔI / Δt) changes, creating this flux.

Thus, the magnitude of the electromotive force of self-induction arising in the conductor is proportional to the rate at which the current in it changes.
If we take conductors of different shapes, then it turns out that having the same rate of current variation, the electromotive forces of self-induction arising in them will be different.

So, if you take a coil and then stretch it in one turn, then at the same speed with which the current changes, the EMF of the self-induction coil will be larger. This is due to the fact that each line of force, pinning coil turns, adheres to it more times than with one turn.

The value characterizing the relationship between the speed with which the current changes in the circuit and the self-inductance EMF that occurs while this is the inductance of the circuit.

We denote the inductance of the coil by the letter L; Then the dependence of the magnitude of the electromotive force of self-induction on the speed with which the current changes takes place can be expressed by the following formula:

E = -L (ΔI / Δt)

From here

Units L = (unit E ˖ unit t) / (unit I)

Assuming that in this formula Δt = 1 sec, ΔI = 1 ampere and E = 1 volt, we get:

Units L = 1 (in ˖ sec / a)

This unit is called Henry (HH).

Consequently,

1 H = 1 (in ˖ sec / a)

So, Henry is the coil inductance, in which a current change of 1 amperes per second excites an electromotive force of self-inductance equal to 1 volt.
To measure small inductances, thousandths of Henry-milligeny (mH) and millionths of Henry-Microgen (μH) are used.

In addition, often used and another unit - a centimeter of inductance, and 1 μH = 1000 cm inductance.

In this way,

1 H = 1000 mH = 1000000 mH = 1000000000 cm

The inductance of the coil depends on its number of turns, shape and dimensions. The more the number of turns in the coil of self-induction, the greater its inductance.

Also, self-induction, the inductance of the coil significantly increases when inserting its core of iron or some other magnetic material inside.
The windings of electromagnets in generators and motors have a large inductance, at the moment of opening the circuit, when the rate of change of the electric current (ΔI / Δt) is very high, a large EMF of self-induction can arise in these windings, which, if not taken, will lead to breakdown Insulation of windings.