Q. Equal currents are flowing in three infinitely long wires along positive x, y and z directions. The magnetic field at a point (0, 0, -a) would be (*i* = current in each wire )

(a) $ \displaystyle \frac{\mu_0 i}{2\pi a} (\hat{j}-\hat{i}) $

(b) $\displaystyle \frac{\mu_0 i}{2\pi a} (\hat{i}-\hat{j}) $

(c) $\displaystyle \frac{\mu_0 i}{2\pi a} (\hat{j}+\hat{i}) $

(d) $ \displaystyle \frac{\mu_0 i}{2\pi a} (-\hat{i}-\hat{j}) $

Ans: (a)