Physics - Current Electricity Question with Solution | TestHub

A. For cells in series, total EMF $=2\mathcal{E}$ and total internal resistance $=2r$. Current $I_S=2\mathcal{E}/(2r+R)$.

B. For identical cells in parallel, equivalent EMF $=\mathcal{E}$ and equivalent internal resistance $=r/2$. Current $I_P=\mathcal{E}/(r/2+R)$.

C. For maximum power transfer in the series case, the external resistance must equal the total internal resistance, so $R=2r$. D. For maximum power transfer in the parallel case, $R=r/2$, not $R=r$.