Electrical Power & Heating Effect question from NEET 2012 (AIPMT, Mains)

Answer: (c)

1. $R$ and $5\ \Omega$ are in parallel across 10 V.
2. $P = \dfrac{V^2}{R} + \dfrac{V^2}{5} = \dfrac{100}{R} + 20 = 30$.
3. $\dfrac{100}{R} = 10 \Rightarrow R = 10\ \Omega$.
4. So the answer is (c) $10\ \Omega$.