Question

A coil of inductance 300 mH and resistance 2 $\Omega$ is connected to a source of voltage 2 V. The current reaches half of its steady state value in

• A. 0.15 s
• B. 0.3 s
• C. 0.05 s
• D. 0.1 s

Answer 1

Answer: (D)

0.1 s

Answer 2

The charging of inductance is given by
$I = I_0 [1 - e^{-Rt/L} ]$
$\therefore \: \frac{I_0}{2} = I_0 [ 1 - e^{-RT/L} ]$
or $e^{-Rt/L} = \frac{1}{2}$ or $\frac{Rt}{L} =$ 1n 2
or $t = \frac{0.693 \times 300 \times 10^{-3}}{2}$
= 0.1 s