Define current sensitivity and voltage sensitivity of a galvanometer.

Current sensitivity of a galvanometer is defined as the deflection produced in the galvanometer when a unit current flows through it.

\(I_s=\frac{\theta}{I}=\frac{nBA}{c}\)

Where n is no of turns in the coil of galvanometer,  B is Magnetic field around coil, A is Area of coil and c is restoring torque per unit twist.

Voltage Sensitivity of a galvanometer is defined as the deflection produced in the galvanometer when a unit voltage is applied across two terminals.

\(V_s=\frac{\theta}{V}=\frac{\theta}{IR}=\frac{nBA}{cR}=\frac{I_s}{R}\)

Current sensitivity does not depend upon resistance(R), whereas voltage sensitivity does, as evident from their expressions. Current sensitivity can be increased by increasing the number of turns of the coil. However, this increases the resistance of the coil also(R is proportional to length of conductor). Since voltage sensitivity decreases with increase in resistance of the coil, the effect of increase in number of turns is nullified in the case of voltage sensitivity. Hence, there is no increase in voltage sensitivity.