Question

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

• A. $0.1s$
• B. $0.3s$
• C. $0.05s$
• D. $0.5s$

Answer 1

The correct option is A $0.1s$

$I=I_0(1-\exp (\frac{-Rt}{L})t=\tau \ln \left(\frac{I_0}{I_0-I}\right)=\frac{L}{R}\ln 2=0.693\frac{L}{R}=0.693\times \frac{0.3}{2}=0.1s$