Wattless Current

According to NCERT Class 12, Chapter 7 (Alternating Current), the average power in an AC circuit is $P=V_{rms}{I}_{rms}\cos \varphi$, and in a purely capacitive circuit the current leads the voltage by exactly ninety degrees, so $\varphi =90^{\circ }$ and $\cos 90^{\circ }=0$. Consequently the average power is zero, and the current in such a circuit is called a wattless current because it transfers no net energy over a cycle. The option claiming maximum power stored permanently is wrong; a capacitor stores energy during one quarter-cycle and returns it during the next, storing nothing permanently. The option claiming heat dissipation is incorrect because an ideal capacitor has no resistance and cannot dissipate energy as heat. The option equating power to $V_{rms}{I}_{rms}$ ignores the power factor and describes apparent, not real, power. A plausibility check: since energy merely oscillates between source and capacitor field without net loss, zero average power is entirely consistent with energy conservation. The same conclusion applies to a purely inductive circuit, where the current instead lags the voltage by ninety degrees, again giving a zero power factor and a wattless current. Real circuits always contain some resistance, so in practice a small amount of power is dissipated, but the idealised limit clarifies that only resistive elements consume average power while purely reactive elements do not. This principle explains why utility companies charge industrial consumers based partly on power factor: a load carrying large wattless currents draws heavy currents that stress the supply lines without performing useful work, so correcting the power factor benefits both the consumer and the grid.