1. The problem statement, all variables and given/known data A series R-L transient circuit is connected to a voltage source of E= 40V through a switch as shown. Suppose the switch is closed at time t=0μs and it was observed that the current iL flowing through the inductor rises to 4mA at time t=20μs and remains at 4mA after t=20μs. (i) Find the R-L time constant τ in μs for the storage phase. Resistor given is 10kΩ 3. The attempt at a solution iL=E/R(1-e-t/τ) 0.004=40/10000(1-e-20x10-6/τ) 0.004=0.004(1-e-20x10-6/τ) -> 0.004-0.004=0 0=-e-20x10-6/τ -> Wanted to take ln for both side, ln 0 =error unable to continue, please help, thanks. (ii) Calculate the amount of energy Wl in nJ, stored in the inductor after 1 minute. How do we know 1min=60sec>>5time constant?