State the principle of moving coil galvanometer. Explain its working and obtain the expression for the deflection produced due to current passed through the coil. Define the current sensitivity.
When a current carrying coil is placed in a magnetic field, its experiences a torque which causes a coil to rotate at a certain angle.
When the current is passed through the coil, it experiences a torque which expressed as;
where,
N = number of turns
A = area
B = magnetic field
I = current
then,
then,
Restoring torque
at equilibrium,
,
is the current sensitivity.
Current sensitivity is defined as the deflection per unit current.