A coil having inductance 2.0 H and resistance `20 Omega` is connected to a battery of emf 4.0 V. Find (a) the current a the instant 0.20 s after the connection Is made and (b) the magnetic energy at this instant.

Explanation

Here L=2.0H
`R=20W, emf =4.0V,`
`t=0.20s`
`i_0=(e/R)=(4/20)`
`and tau=(L/R)=(2/20)=0.1`
`(a) i=i_0(1-r^(-t//tau)`
`=(4/20)(1-r^(-0.2//0.1)`
`=(1/5)(1-e^-2) = 0.17A `
` (b) 1/2Li^2 = 1/2 xx 2(0.17)^2`
` = 0.0289 = 0.03J.`