The switch in the circuit shown below has been closed for a long time before it is opened at t = 0. Find the current i(t) through the inductor for t ? 0. Assume R1 = 400 ?, R2 = 2 k?, R3 = 1 k?, R4 = 6 k?, Vs = 2 V, L = 90 mH.
Ra = R2 || R3 || R4 = 0.6 k?
VR3(0) = Vs × Ra/(R1 + Ra) = 1.2 V
i(0) = I0 = VR3(0)/R3 = 1.2 mA
Req = R3 + (R2 || R4) = 2.5 k?
? = L/Req = 36 ?s, 1/? = 27777.7778 (1/s)
i(t) = 1.2 e-27777.7778t u(t) mA
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