Deformation of Flexible Current Loop in Magnetic Field – Rankers Physics
Topic: Magnetic Effects of Current
Subtopic: Force Acting on Current Carrying Conductor

Deformation of Flexible Current Loop in Magnetic Field

Assertion (A): If a flexible loop (irregular shape) carrying current is located in an external uniform magnetic field then it may be changed to circular shape.
Reason (R): A current carrying loop in uniform magnetic field has zero net force.
 
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Solution:

Assertion (A) is true: A current loop in a magnetic field tends to maximize its enclosed area to minimize its magnetic potential energy \(-\vec{M} \cdot \vec{B}\). A circle provides the maximum area for a given perimeter.

Reason (R) is true: The net force on a closed loop in a uniform magnetic field is zero. (R) does not explain (A); the shape change is due to torque and area maximization, not the zero net force. Both are true, but (R) is not the explanation for (A).

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