A coil having resistance `15 Omega` and inductance `10H` is connected across a `90` Volt `dc` supply. Determine the value of current after `2sec`, What is the energy stored in the magnetic field at that instant.

Explanation

Here, `R = 15 Omega, L = 10 H, E = 90 V`,
`I_(0) = E//R = 90//15 = 6 A, I = ?, t = 2 s`
`tau = L//R = 10//15 = (2)/(3) s`
`I = I_(0) (1 - e^((-R)/(L)t))`
` I = 6 (1 - e^(-2 xx (3)/(2))) = 6 (1 - 0.05) = 5.7 A`
Energy stored in mag. field ` =(1)/(2) LI^(2)`
` = (1)/(2) xx 10 (5.7)^(2) = 162.45` joule