In electricity there are two forms of inductance. Mutual inductance and self inductance.

Mutual inductance is what happens in a transformer. When changing current in one  oil causes a current in another coil. The unit of mutual inductance is Henry (H)

Change in Magnetic field is proportional to current.

That is  φ / I is a constant (M)     Therefore  φ = m X i.

We know that  Volts = change in flux / time.  That is          V =  N x  Δ φ  / Δ t.

                   ( N is the number of turns)

Substituting the value of φ  in the above we get :-            V = M . Δ I  /   Δ t.

Uses.

Inductors are used to tune radio circuits, filter out unwanted noise and in various other electronic circuits.

Example 1.

 The current in primary increases from zero to 0.8A in 2.5 s. The secondary coil Voltage was 1.2 v.

Inductor and self induction..

An inductor can simply be a coil of wire with a several attached to an electrical circuit.  When a current is passed it develops a strong magnetic field. According to Faraday’s law , when the current is building up , as there is a change in magnetic flux, a current is induced. According to Lenz’s law the induced current will be in the opposite direction to the current that caused the change. So this is sometimes referred to as the back emf.

When the inductor is charging  the equation  V= ir  has to be modified as  

  Supplied voltage  - Inductor voltage = ir.

This can be written as  Vs - VL  = ir

Charging and Discharging an Inductor.

When the circuit is switched on,  the bulb glows brightly and becomes dim. Then again when switched off the bulb becomes bright and goes off.

Let us use the following data for a calculation:-

Supply voltage   =  1.5 V.

Normal resistance of circuit =  0.3 Ω.

Time taken for current to be steady  = 0.2 seconds.

Inductance of coil   = 0.3 H

Energy stored in an inductor

J = ½ L x I 2

Unit for Inductance.

The basic unit of measurement for inductance is the Henry, ( H )

It can also be given as  Webers per Ampere ( 1 H = 1 Wb/A ).

Example 2