Question

A loop of flexible wire of irregular shape carrying current is placed in an external magnetic field. Identify the effect of the field on the wire.

• A. shape of the loop remains unchanged
• B. loop assumes circular shape with its plane normal to the field
• C. loop assumes circular shape with its plane parallel to the field
• D. wire gets stretched to become straight

Hint:

Magnetic systems always work towards the state of minimum potential energy, which corresponds to maximum magnetic flux.

Answer 1

The Correct Option is B

Step 1: A current loop in a magnetic field experiences a force that tends to maximize the magnetic flux passing through it.
Step 2: For a given perimeter, a circle has the maximum area. Thus, the flexible wire expands into a circular shape.
Step 3: To maximize flux ($\Phi = BA \cos \theta$), the plane of the loop aligns perpendicular to the field ($\theta = 0^\circ$).