Current sensitivity is the measure of responsiveness of any instrument to the change of current through it.
Or
Current sensitivity : It is defined as the deflection of coil per unit current flowing in it.
Current Sensitivity,
Voltage sensitivity is the measure of responsiveness of any instrument to the change of applied voltage across it.
Or
Voltage sensitivity : It is defined on the deflection of coil per unit potential difference across its ends.
Voltage Sensitivty,
where G is resistance of galvanometer.
Justification: When number of turns N is doubled, then the current sensitivity (∝ N) is doubled; but at the same time, the resistance of galvanometer coil (G) will also be doubled, so voltage sensitivity (Sv ∝ N/G) will remain unchanged; hence inreasing current sensitivity does not necessarily increase the voltage sensitivity.