A coil o finductanc e`8.4mH` and resistance `6Omega` is connected to a `12V` battery. The current in the coil is 1.0A` in the time (approx .)

Options

A. `500sec`
B. `20sec`
C. `35msec`
D. `1msec`

Answer

D

Explanation

`i=(E)/(R)(1-e^(-(Rt)/(L)))`
`i=(12)/(6)[1-e^(-(6xxt)/(8.4xx10))]`
`(t)/(e^(1.4xx10^(-3)))=2`
`(t)/(1.4xx10^(-3))=1n2=0.7`
`t=0.98xx10^(-3)=1msec`