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 growth of current in LR circuit is given by

$I = I_{0}\lbrack 1 - e^{- Rt/L}\rbrack$

Or $e^{- Rt/L} = \frac{1}{2}$ or $\frac{Rt}{L} = In2 \Rightarrow t = \frac{L\ln 2}{R}$

or $t = \frac{300 \times 10^{- 3} \times 0.693}{2} = 0.1s$