Cells: EMF, Internal Resistance & Combinations question from NEET 1990 (AIPMT)

Answer: (b)

1. Maximum power in $R$ occurs when $R = r_{eq}$: $P_{max} = \dfrac{E_{eq}^2}{4r_{eq}}$.
2. Series: $E_{eq} = 4\text{ V}$, $r_{eq} = 2\ \Omega$, $P_{max} = \dfrac{16}{8} = 2\text{ W}$.
3. Parallel: $E_{eq} = 2\text{ V}$, $r_{eq} = 0.5\ \Omega$, $P_{max} = \dfrac{4}{2} = 2\text{ W}$.
4. So the answer is (b) 2.0 W.