A person turns the handle of a small ac generator. The generator lights a 12 W lamp for 5 minutes. The generator changes 80% of the work done on it into electrical energy. The work done by the person is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 4500 J
The generator changes the work done by the person into electrical energy, and the lamp uses this energy. Only 80% of the work reaches the lamp, so the work done is more than the energy the lamp uses.
\( P=12\ \mathrm{W} \)
\( t=5\ \mathrm{min}=300\ \mathrm{s} \)
Electrical energy used by the lamp:
\( \begin{aligned} E &= Pt \\ &= 12\times300 \\ &= 3600\ \mathrm{J} \end{aligned} \)
Work done by the person:
\( \begin{aligned} W &= \frac{E}{0.8} \\ &= \frac{3600}{0.8} \\ &= 4500\ \mathrm{J} \end{aligned} \)
NCERT (2026-27):
AC Generator – “… An ac generator converts mechanical energy into electrical energy.”