A storage battery of emf 10 V and internal resistance 1 Ω is being charged by supply of 120 V dc using a resistor of 10 Ω. The potential difference across the battery is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 20 V
While a battery is being charged, current is driven into it against its emf, from its positive terminal to its negative terminal. The terminal voltage is then the emf plus the drop across the internal resistance.
The charging current is set by the net emf acting in the circuit:
\( \displaystyle I = \frac{V_{\mathrm{supply}} - E}{R + r} \)
\( \displaystyle I = \frac{120\,\mathrm{V} - 10\,\mathrm{V}}{10\,\Omega + 1\,\Omega} = 10\,\mathrm{A} \)
\( \displaystyle V = E + Ir \)
\( \displaystyle V = 10\,\mathrm{V} + (10\,\mathrm{A})(1\,\Omega) = 20\,\mathrm{V} \)
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 – …
