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A 0.03 H inductor and a 0.15 kohm resistor are joined in series with a 15 V battery. The switch K1 has been closed a long time. At t = 0, K1 is opened and K2 is closed at the same instant, so the inductor now discharges through the resistor. Find the current at t = 1 ms (use e⁵ = 150).

1. 0.67 mA
2. 6.7 mA
3. 100 mA
4. 67 mA

Correct answer: 0.67 mA

Solution

Before switching, the inductor carries the steady current I0 = V/R. After K1 opens and K2 closes, the inductor current decays exponentially with time constant L/R. Evaluate at t = 1 ms using e⁵ = 150.

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