Galvanometer

A current carrying coil placed in a magnetic field experiences a torque & deflects.

This deflection is calibrated to measure current flowing in it. Used to detect & measure only small currents of the order of microamperes. Current sensitivity (I_s): It is defined as the deflection produced for a unit current. i.e. . I_s can be increased by increasing B or by decreasing k (by taking quartz or phosphorous bronze). Reciprocal of current sensitivity is called ‘figure of merit’. As we have discussed that a galvanometer fails to measure currents I > I_g. In order to measure currents I > I_g we use an Ammeter.