4.11 THE MOVING COIL GALVANOMETER

Currents and voltages in circuits have been discussed extensively in Chapters . But how do we measure them? How do we claim that current in a circuit is . A or the voltage drop across a resistor is .

V? Figure . exhibits a very useful instrument for this purpose: the moving Conversion of galvanometer into ameter and voltmeter: !" !"#$% "& coil galvanometer (MCG). It is a device whose principle can be understood on the basis of our discussion in Section .

. The galvanometer consists of a coil, with many turns, free to rotate about a fixed axis (Fig. . ), in a uniform radial magnetic field.

There is a cylindrical soft iron core which not only makes the field radial but also increases the strength of the magnetic field. When a current flows through the coil, a torque acts on it. This torque is given by Eq. ( .