Question

State the principle of the working of a moving coil galvanometer, giving its labeled diagram ?

Answer 1

Moving coil Galvanometer 

Principle: 

Its working is based on the fact that when a current carrying coil is placed in a magnetic field, it experiences a torque.

Working: 

Suppose the coil PQRS is suspended freely in the magnetic field. 

Let 

l = Length PQ or RS of the coil 

b = Breadth QR or SP of the coil 

n = Number of turns in the coil 

Area of each turn of the coil, A = l × b

Let B = Strength of the magnetic field in which coil is suspended

I = Current passing through the coil in the direction PQRS 

Let, at any instant, α be the angle which the normal drawn on the plane of the coil makes with the direction of magnetic field.

The rectangular coil carrying current when placed in the magnetic field experiences a torque whose magnitude is given by,

τ = nIBA sin α