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 (Is): It is defined as the deflection produced for a unit current. i.e. . Is 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 > Ig. In order to measure currents I > Ig we use an Ammeter.