A galvanometer is a small electric current indicator. It shows the presence, strength, or direction of small electrical currents.
A ballistic galvanometer has a coil of very thin insulated copper wire suspended by means of a phosphor-bronze fiber between two strong poles of magnet. When a small momentry current passes through the coil then the coil experiences a torque =MXBwhere M is magnetic dipole moment of the coil and Bis the magnetic field .due to this torque the coil turns with a jerk . the deflection of the coil varies in proportion of the strength of current, which is measured with the help of lamp and scale arrangement .