Finding V(l) for t>0 in RL circuit
In these solution i have shown  RL and RC Transient Responses,We saw that the currents and voltages in RL and RC circuits decay exponentially with time, with a characteristic time constant t, when an applied current or voltage is suddenly removed.
In general, when an applied current or voltage suddenly changes, the voltages and currents in an RL or RC circuit will change exponentially with time, from their initial values to their final values, with the characteristic time constant t.
 



i hope it helps you.