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 the figure, the loop will

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

Answer 1

Answer: (C)

move towards the wire

Answer 2

Straight wire will produce a non-uniform field to the right of it. $F_{bc}and F_{da}$will be calculated by integration but these two forces will cancel each other. Further force on wire ab will be towards the long wire and on wire cd will be away from thelong wire. But since the wire ab is nearer to the long wire force of attraction towards the long wire will be more. Hence, the loop will move towards the wire.
$\therefore$ Correct option is (c).