Physics > magnetism-induction-and-alternating-current > Moving Charges And Magnetism

**Case Study:** A galvanometer is an instrument used to show the direction and strength of the current passing through it. In a galvanometer, a coil placed in a magnetic field experiences a torque and hence gets deflected when a current passes through it. The name is derived from the Italian scientist L. Galvani, who in 1791 discovered that electric current makes a dead frog''s leg jerk. In equilibrium: $NBAI = k\phi$, where $N$ = number of turns, $A$ = area of each turn, $B$ = radial magnetic field, $k$ = torsional constant of spring, $\phi$ = angular deflection. As $I_g$ (full scale deflection current) is very small, a shunt resistance is connected in parallel to convert it to an ammeter; a high resistance in series converts it to a voltmeter.