Q135 / 180 · COMEDK 2026 (9 May Shift 1) · Physics
If wattless current flows in an AC circuit, then the circuit is:
- ALR circuit
- Correct answerBPurely capacitive circuit
- CPurely resistive circuit
- DLCR circuit
Solution
The average power dissipated in an AC circuit is given by $P = V_{rms} I_{rms} \cos \phi$, where $\phi$ is the phase difference between the voltage and the current.
For wattless current, the average power dissipated must be zero, which means $P = 0$.
This implies $\cos \phi = 0$, so the phase difference $\phi = \dfrac{\pi}{2}$ or $-\dfrac{\pi}{2}$.
A phase difference of $\dfrac{\pi}{2}$ occurs only in purely inductive or purely capacitive circuits. In a purely capacitive circuit, the current leads the voltage by exactly $\dfrac{\pi}{2}$, making the power factor zero.
Therefore, wattless current flows in a purely capacitive circuit.
Answer: Purely capacitive circuit
For wattless current, the average power dissipated must be zero, which means $P = 0$.
This implies $\cos \phi = 0$, so the phase difference $\phi = \dfrac{\pi}{2}$ or $-\dfrac{\pi}{2}$.
A phase difference of $\dfrac{\pi}{2}$ occurs only in purely inductive or purely capacitive circuits. In a purely capacitive circuit, the current leads the voltage by exactly $\dfrac{\pi}{2}$, making the power factor zero.
Therefore, wattless current flows in a purely capacitive circuit.
Answer: Purely capacitive circuit
Hence, the correct answer is option: 'B'.