(a) Moving coil galvanometer is an instrument used for detection and measurement of small currents. Moving coil galvanometer works on the principle that when a current-carrying coil is placed in magnetic field it experiences a torque.
(b) A galvanometer cannot be used to measure the value of the current because of following two reasons:
(i) Galvanometer is a very sensitive device, it shows large deflection when small currents pass through it.
(ii) Galvanometer has very high resistance which can alter the value of current flowing in circuit.
(c) (i) Voltage sensitivity is defined as the deflection produced in the galvanometer when a unit voltage is applied across the two terminals of the galvanometer:
(ii) Current sensitivity is defined as the deflection produced in the galvanometer when a limit current flow through the galvanometer:
where N is number of turned in coil, B is the magnetic field, A is the area of the coil, K is the restoring torque per limit twist.
