A \( 80\,\Omega \) resistor is connected to a 240 V, 50 Hz ac supply. The net power consumed over a full cycle is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 720 W
In a purely resistive ac circuit the voltage and current are in phase, so the power is positive at every instant. The average power over a full cycle uses rms values, and the 240 V rating of an ac supply is its rms value.
\( \displaystyle P = \frac{V_{\mathrm{rms}}^{2}}{R} \)
\( \displaystyle P = \frac{(240\,\mathrm{V})^{2}}{80\,\Omega} = \frac{57600}{80} = 720\,\mathrm{W} \)
Note: NTA picked this question from an NCERT (2026-27) exercise and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Exercises – …
