Question

Two straight horizontal parallel wires are carrying the same current in the same direction, and 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 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 verticle circle of radius and centre halfway between the wires
• D. At points halfway between the wires in the horizontal plane

Answer 1

The correct option is A

At a distance d/2 from any of the wires

Given Data.

The same current is flowing in the same direction through two horizontal, straight wires; the distance between the wires is d.

The correct option (A)

The orientation of the needle will be independent of the amount of current flowing through the wires at a distance of d/2 from any one of them because the Lorentz force exerted by the two wires will be equal and moving in the opposite direction.

The incorrect options (B), (C), (D)

Option (B)

In the horizontal plane, it can not be independent. Thus option B is incorrect.

Option(C)

Because of a circulated movement, it cant be independent. Thus option C is incorrect.

Option (D)

In the horizontal plane, it can not be independent. Thus option D is incorrect.

Therefore the correct option is A.