Which of the following circuits shows the maximum power dissipation?

The correct answer is Option (3) → Purely resistive circuit

The average power in an ac circuit is \( P=VI\cos\phi \). Here \( \phi \) is the phase difference between the voltage and the current, and \( \cos\phi \) is the power factor.

Option (1) Purely capacitive circuit — Incorrect. The current leads the voltage by \( \pi/2 \). So \( \cos\phi=0 \), and no average power is dissipated. A current still flows, called the wattless current.

Option (2) Purely inductive circuit — Incorrect. The current lags the voltage by \( \pi/2 \), so again \( \cos\phi=0 \) and the average power is zero.

Option (3) Purely resistive circuit — Correct. The voltage and current are in phase, so \( \phi=0 \) and \( \cos\phi=1 \), the largest possible power factor. The power \( P=VI \) is the maximum power dissipation.

NCERT (2026-27):
Power in AC Circuit: The Power Factor – “… Case (i) Resistive circuit: If the circuit contains only pure R, it is called resistive. In that case φ = 0, cos φ = 1. There is maximum power dissipation.”