Q.What is wattless current?

[!TLDR] Wattless (idle) current is the AC current through a purely reactive element (pure L or pure C) that dissipates zero average power, since the voltage-current phase difference there is exactly $90^\circ$, making $\cos\phi=0$. [!ANSWER] Wattless current is the current in a pur …

The average power dissipated in any AC circuit is $P_{av}=e_{rms}\,i_{rms}\cos\phi$, where $\phi$ is the phase difference between voltage and current. In a purely inductive or a purely capacitive circuit, this phase difference is exactly $90^\circ$ (current either lags or leads the voltage by a full quarter cycle), so the power factor $\cos\phi=\cos90^\circ=0$ -- meaning $P_{av}=0$ regardless of how large the rms current actually is. A current that genuinely flows through the circuit, and can even be quite large in magnitude, but delivers zero net power to the circuit over a complete cycle (because energy is merely exchanged back and forth with the source rather than being permanently consumed) is called the WATTLESS or IDLE current. It arises specifically from the purely reactive part of a circuit (pure L or pure C); the resistive …

Apply the general power formula $P_{av}=e_{rms}i_{rms}\cos\phi$ to the $\phi=90^\circ$ case of a pure inductor or capacitor, where $\co …

Assuming that if current flows, power must be dissipated -- missing that the PHASE relationship between voltage and current, not merely the current' …