B4. Referring to the R-L circuit in Fig. B4, an inductor, with internal resistance R3=10, will be charged when the switch SW is closed at t=0 s. Fig. B4 Determine: (a) the time constant ; (b) the equation for voltage vL in terms of t; (c) the time for vL to reach its steady state; (d) the equation for current it in term of t; and (e) the current iL flowing through the inductor L at t=0,,2,3,4 and 5. (f) Plot the graph of current iL against time t from t=0 to 5. (g) Calculate the new value of L if the time for the current is to reach its steady is shorten to 15ms