Moving coil galavanometer is an instrument used for the detection and measurement of small currents.
Principle : The working of moving coil galvanometer is that when a current carrying coil is placed in a varying magnetic field, it experiences torque.
Torque acting on a rectangular current carrying coil:
Let, the coil PQRS be freely suspended in a magnetic field.
Let,
l = length of PQ or RS of the coil,
b = breadth of QR or SP of the coil,
n= number of turns in the coil,
B= strength of magnetic field in which the coil is suspended,
I = current passing through the coil in the direction PQRS.
Then,
Area of the coil, A = l b
At any instant, is the angle which the normal drawn on the plane of the coil makes with the direction of magnetic field.
The rectangular current carrying coil, when placed in a magnetic field experiences a torque whose magnitude is given by,
Current sensitivity of a moving coil galvanometer depends on :
i) Number of turns of the coil
ii) Magnetic field applied.