Question

Two straight horizontal parallel wires are carrying the same current in the same direction; d is the distance between the wires. You are provided with a small freely suspended magnetic needle. At which of the following positions will the orientation of the needle be independent of the magnitude of the current in the wires

• A. At a distance $d / 2$ from any of the wires
• B. At a distance $d / 2$ from any of the wires in the horizontal plane
• C. Anywhere on the circumference of a vertical circle of radius d and centre halfway between the wires
• D. At points halfway between the wires in the horizontal plane

Answer 1

Answer: (D)

At points halfway between the wires in the horizontal plane

Answer 2

At these points, the resultant field $= 0$