Magnetic Field of Straight Wires question from MHT CET 2025 (21 Apr, Shift 1)

Answer: (a)

1. P is outside both wires: $r$ from the near wire and $3r$ from the far wire. Same-direction currents give fields in the same direction at an outside point.
2. $B = \frac{\mu_0 I}{2\pi r} + \frac{\mu_0 I}{2\pi (3r)} = \frac{\mu_0 I}{2\pi r} \cdot \frac{4}{3}$
3. $B = \frac{2}{3}\frac{\mu_0 I}{\pi r}$
4. So the answer is (a).