Question

Two straight, infinitely long and thin parallel wires are spaced 0.1m apart and carry a current of 10 ampere each. The ratio of the magnetic fields, at a point at a distance of 0.1m from both wires, for the two cases. When the currents are in (i) same direction and (ii) opposite directions; would be

(1) 1 : 1

(2) √3 : 1

(3) 1 : √3

(4) √2 : 1

Answer 1

(2) √3 : 1

Since point ‘P’ is situated equidistant from the wires A and B, hence magnitude of magnetic field at point P due to both the wires will be same.

(i) When wires carry currents in same direction (Fig. 1)

(ii) When wires carry currents in opposite direction (Fig. 2)

Hence ratio of magnetic fields in two cases