A car has a fresh storage battery of e.m.f. 15 V and internal resistance \( 4\times10^{-2}\,\Omega \). If the starter motor draws a current of 85 A, what is the terminal voltage of the battery when the starter is on?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 11.6 V
The terminal voltage of a cell that is supplying current is its emf minus the drop across its internal resistance.
\( V = E - I\,r \)
\( I\,r = 85\,\mathrm{A} \times 4\times10^{-2}\,\Omega = 3.4\,\mathrm{V} \)
\( V = 15\,\mathrm{V} - 3.4\,\mathrm{V} = 11.6\,\mathrm{V} \)