The principle of working of a moving coil galvanometer is based on the fact that if a current carrying coil is placed in a uniform radial field, it experiences a torque.
A galvanometer cannot be used as such to measures current in a circuit due to following two reasons:
(i) Galvanometer is very sensitive. It gives full scale deflection with a quite small current (nearly few micro ampere).
(ii) In order to measrue the current, the galvanometer has to be connected in series of circuit. As its resistance is large, its presence in the circuit will decrease the effective current in the circuit.
