Question

When 100 V d.c. is applied across a coil, a current of 1 A flows through it. When 100 V a.c. of 50 Hz is applied to the same coil only 0.5 A flows. The inductance of the coil is

• A. 0.55 mH
• B. 5.5 mH
• C. 0.55 H
• D. 55 mH

Answer 1

Answer: (C)

0.55 H

Answer 2

R = $\frac{V}{I} = \frac{100}{1} = 100 \, \Omega$ and Z = $\frac{V}{I} = \frac{100}{0.5} = 200 \, \Omega$
L = $\frac{Z^2 - R^2}{2 \pi \nu} = \frac{200^2 - 100^2}{2 \times \frac{22}{7} \times 50}$ = 0.55 H