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