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In an RC charging circuit (capacitor initially uncharged), find the displacement current through the capacitor plates after a time equal to one time constant (tau = RC). Given the initial (maximum) current is 120 mA.

1. 120/e mA
2. 120/e² mA
3. 120 mA
4. None of these

Correct answer: 120/e mA

Solution

For a charging capacitor, the conduction current i = (V/R)*e^(-t/tau). Displacement current through the capacitor equals this conduction current (Maxwell's concept). At t = tau: i = (V/R)*e^(-1) = 120/e mA.

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