Question

A rectangular loop carrying a current $i$ is situated near a long straight wire such that the wire is parallel to one of the sides of the loop and is in the plane of the loop. If steady current I is established in the wire as shown in fig., the loop will

• A. rotate about an axis parallel to the wire
• B. move away from the wire
• C. move toward the wire
• D. remain stationary

Answer 1

The correct option is C move toward the wire

The long straight wire and side $AB$ carry current in the same direction, hence will attract each other.
The long straight wire and side $CD$ carry current in the opposite direction, hence will repel each other.
Force on side $BC$ will be equal and opposite to force on side $DA$.
Since $CD$ is farther from the wire than $AB,$ the force of attraction on $AB$ will exceed the force of repulsion on $CD$.
Hence, there will be a net force of attraction on the loop $ABCD$ and it will move towards the wire.