Force on Current-Carrying Conductors question from MHT CET 2024 (15 May, Shift 1)

Answer: (d)

1. Force per unit length between parallel wires: $\frac{F}{l} = \frac{\mu_0 I_1 I_2}{2\pi b}$
2. With $I_1 = I_2 = I$: $\frac{F}{l} = \frac{\mu_0 I^2}{2\pi b} = \frac{\mu_0}{4\pi}\cdot\frac{2I^2}{b}$
3. So the answer is (d) $\frac{\mu_0}{4\pi}\left(\frac{2I^2}{b}\right)$.