Biot-Savart Law & Circular Coils question from MHT CET 2026 (15 May, Shift 1)

Answer: (b)

1. Single-turn coils: $B = \frac{\mu_0 I}{2r}$; equal $B$ needs $I \propto r$.
2. Same wire (same area, same material): $R_{wire} \propto \text{length} = 2\pi r$, so $R_{wire} \propto r$.
3. $V = IR_{wire} \propto r^2 \Rightarrow \frac{V_A}{V_B} = \left(\frac{2}{1}\right)^2 = 4$
4. So the answer is (b) $4 : 1$.