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

$\begin {array} {1 1} (A)\;0.05s & \quad (B)\;0.1s \\ (C)\;0.15s & \quad (D)\;0.2s \end {array}$

$I=I_0 \bigg( 1-e^{-\large\frac{R}{L}t} \bigg)$
$0.693 =\large\frac{R}{L}t$
$t = \large\frac{3 \times 0.693}{2}$ $= 0.2 \: sec$
Ans : (D)
edited Mar 24, 2014