mutual induction

MUTUAL
INDUCTION

The
phenomenon of production of induced current in one coil due to change of
current in a neighboring coil is called mutual induction. Suppose a system of two coils A and B
placed close to each other The coil A is connected to a battery and a switch,
while a sensitive galvanometer is connected to the coil B. We observe that as
soon as the switch of the coil A is closed, the galvanometer shows a momentary
deflection.

Similarly,
when the switch is opened, the galvanometer again shows a deflection but this
time its direction is opposite to that of the previous case. 

We can explain these observations using
Faraday's law of electromagnetic induction. When the switch of coil A is
closed, a current begins to flow in the coil due to which magnetic field is
developed across the coil.

Some of the magnetic lines of force of
this field start passing through the coil B. Since current is changing in the
coil A, hence number of magnetic lines of force across the coil B also changes
due to which a current is induced in the coil B in accordance with Faraday's law.

When current in the coil A becomes
steady, number of magnetic lines of force across the coil A also becomes constant. 

Therefore, there is no more change in
number of magnetic lines of force through the coil B due to

which induced current in coil B reduces to zero.

Similarly, when the switch of the coil A is opened, the flow of current through
it stops and its magnetic field reaches to zero.

The number of magnetic lines of force through the coil B decreases to zero due
to which current is again induced in it but in opposite direction to that in
the previous case