Biot-Savart Law & Circular Coils question from NEET 2026 (Re-neet)

Answer: (b)

1. The two halves are in parallel; $R_{ABC} = \frac{1}{2}R_{ADC}$, so $I_{ABC} = \dfrac{2I_0}{3}$, $I_{ADC} = \dfrac{I_0}{3}$.
2. Both currents go from A to C, so at O their fields are opposite. The straight leads pass through O and give zero.
3. $B = \dfrac{\mu_0}{4r}\left(\dfrac{2I_0}{3}-\dfrac{I_0}{3}\right) = \dfrac{\mu_0 I_0}{12r}$
4. So the answer is (b).