NEIEP Mechanics Practice Exam

What happens to capacitors the instant when power is applied?

1. Current is minimum

2. Current is maximum

3. Voltage is maximum

4. Voltage is minimum

The correct answer is: Current is maximum

When power is applied to a capacitor, it acts like a short circuit for a brief moment. At this initial instant, the capacitor has not yet had time to charge, so it offers very little resistance to the flow of current. As a result, the current flowing into the capacitor is at its maximum value. This phenomenon is due to the relationship between voltage, current, and capacitance described by the equation I = C(dV/dt). Since the voltage across the capacitor is initially zero when it is uncharged, the rate of change of voltage (dV/dt) is at its highest with the application of power, leading to a peak current. As the capacitor begins to charge, the voltage across it starts to increase, and therefore the current gradually decreases as it approaches its maximum voltage. Thus, the condition where current is maximum occurs at the very instant power is applied.