The Switch in the Circuit Shown Below Has Been Closed $t = 0$

Essay

The switch in the circuit shown below has been closed for a long time before it is opened at $t = 0$ . Find the current $i ( t )$ through the inductor for $t \geq 0$ . Assume $R _ { 1 } = 2 \mathrm { k } \Omega , R _ { 2 } = 1 \mathrm { k } \Omega , R _ { 3 } = 15$ $\mathrm { k } \Omega , \mathrm { I } _ { \mathrm { s } } = 3 \mathrm {~mA} , \mathrm {~L} = 200 \mathrm { mH }$ .