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

Options

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

Answer

B

Explanation

The current at any instant is given by `l=l_(0)(1-e^(-Rt//L))`
`l_(0)/2=l_(0)(1-e^(-Rt//L))`
`1/2=(1-e^(-Rt//L))`
`e^(-Rt//L)=1/2`
`(Rt)/L=n2`
`therefore t=L/R "ln" 2`
`=(300 xx 10^(-3))/2xx0.693 =150xx0.693xx10^(-3)`
`=0.10395 sec =0.1 sec`