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A small signal voltage V(t) = V₀ sin ωt is applied across an ideal capacitor C:

1. Current I(t) lags voltage V(t) by 90°.
2. Over a full cycle the capacitor C does not consume any energy from the voltage source.
3. Current I(t) is in phase with voltage V(t).
4. Current I(t) leads voltage V(t) by 180°.

Correct answer: Over a full cycle the capacitor C does not consume any energy from the voltage source.

Solution

In an ideal capacitor, the current leads the voltage by 90°, and over a full cycle, the net energy consumed by the capacitor is zero because the energy stored during one half-cycle is returned during the other half-cycle.

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