A small signal voltage V(t) = V0 sin t is applied across an ideal capacitor C :
Current I(t), lags voltage V(t) by 90o.
Over a full cycle the capacitor C does not consume any energy from the voltage source.
Current I(t) is in phase with voltage V(t).
Current I(t) leads voltage V(t) by 180o.
When an ideal capacitor is connected with an ac voltage source, current leads voltage by 90°. Since, energy stored in capacitor during charging is spent in maintaining charge on the capacitor during discharging. Hence over a full cycle the capacitor does not consume any energy from the voltage source.