Question

A students connects a long air cored coil, of manganin wire, to a 100 V d.c source and records a current of 1.5 A. When the same coil is connected across. (100 V; 50 Hz) a.c source, the current reduces to 1A. Why? Also calculate the reactance of the coil.

Answer 1

In d.c circuit the impedance of the coil, is only due to its resistance ‘R’. Hence

When the same coil is connected to an a.c source, the impedance of the coil is due to both its resistance R and its inductance L. The coil now acts like a LR series circuit, having a impedance

The value of current, in the a.c circuit decreases, because of this increase in impedance of the coil.