Question

A circular loop of wire is carrying a current $ i $ (as shown in figure) on applying a uniform magnetic field inward perpendicular to the plane of the loop:

(A) Contract
(B) Expand
(C) Move along the positive $ x $ direction
(D) Move along the negative $ x $ direction

Answer 1

Hint: Here, in the above given figure we see that the circular loop is carrying current in it in clockwise direction and a uniform magnetic field is shown by a cross symbol which indicates that the direction of the magnetic field is perpendicularly inwards. We have to apply the concept of magnetic field lines, force and the direction of current such that the vector product between current and magnetic field gives direction of force.

Complete step by step answer:
Let us first understand the given figure, then apply the concept of magnetic field direction, force direction and current direction in the loop carrying current in clockwise direction. The magnetic field is in the inward direction as shown by the cross marks in the above figure. We have to apply the concept mentioned above that at any instant when we take a vector product of a magnetic field and current the resultant will give the direction of the force vector.
Here, force will be radially outwards from the loop at any instant. Thus, the outcome of this is that the loop will expand in an outward direction.
The correct answer is option B.

Note:
Here, we have to understand that the magnetic field, force and current are perpendicular to each other and then we obtain the answer that the force is radially outwards. Just remember this concept and answer such questions carefully. The whole problem depends on directions.