help with question 15 and 17 please, explain in detail would be really helpful t

Question

help with question 15 and 17 please, explain in detail would be really helpful thanks

The following three questions refer to the RL circuit: The circuit shown is initially at equilibrium with the switch, S, open. At t=0, the switch is closed. Immediately after the switch is closed the current in L_2 is larger than the current in L_1 a current flows in R_2. all the current flows through the smaller inductor. Assume that the switch has been closed for a long time, and then it is suddenly opened. Find the magnitude of the potential across L_2 immediately after the switch is opened. 5.8 V 15 V 40 V 67 V

Explanation / Answer

Question 15.)

Concept is - the current in inductor doesn't change abruptly .( so just before opening switch = current just after opening circuit )

So current in L1 and L2 both will be zero just after closing the switch.

But current will flow through R1 and R3 .

Question 17.)

After long time inductor behaves like short circuit (unlike capacitor, which behaves like open circuit a)

So current in R1 and R3 will be zero . and all current will pass through L2 (=V/R2)

Current via L1 will also be zero

Now after long time switch is opened so current in inductor won't change just after opening the circuit (I= V/ R2)

And it will flow through L1 and R1 and R3

So potential drop across L2 = I (R1× R3 /(R1+R3)R2 = V×40/39= 40 v

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