First slide
Time -Varying current in L-R circuit
Question

Switch s of the circuit, shown in figure, is closed at t = 0. If e denotes the induced emf in L and i, the current flowing through the circuit at time t, which of the following graphs is correct?

Moderate
Solution

At the time t = 0, e is max and is equal to E, but current i is zero.

 At time t,i=ER(1-e-RtL) Therefore e =Ldidt=EL e-Rt/L. So e decreases exponentially.

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