Question

A current carrying circular loop is freely suspended by a long thread. In what direction, will the plane of the loop point in?
A. Wherever left free
B. North-South
C. East-West
D. At ${45^ \circ }$ with the east-west direction

Answer 1

Hint: When current starts to slow through a circular loop and is maintained, it starts to behave like a bar magnet. A bar magnet, when suspended freely, rests in the north-south direction. Figure out the direction of the magnetic field that flows in a current carrying circular loop and use it to understand the plane of the loop.

Complete answer:
As current starts flowing through a circular metallic loop, it creates a magnetic field around itself.
The magnetic field enters from one face of the loop and then leaves from the other face. In a bar magnet, the magnetic field enters from the north pole and leaves from the south pole. Thus, a current carrying loop behaves like a magnet or as a magnetic moment.

The direction of this magnetic moment is perpendicular to the area of the loop. The face of the loop, in which the current flows in anti-clockwise direction acts like a north pole of a magnet. The face of the loop, in which the current flow in clockwise direction acts like a south pole of a magnet.

Now, we know that a freely suspended bar magnet rests in the north-south direction. The current carrying coil will also rest in a similar way with the axis of the coil being along the north-south direction.
Thus, the plane of the coil will be the one perpendicular to it, that is, the plane of the area of the circular loop. The direction perpendicular to north-south is east-west.

Hence, the direction of the plane of the loop will be in an east-west direction. Thus, the correct option is C.

Note:A solenoid behaves like a bar magnet as well. It behaves as if an imaginary bar magnet is placed along the axis of the solenoid. A circular current carrying loop also behaves like a bar magnet in the same way.