A rectangular loop carrying a current $\mathrm{i}$ 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 the steady current $\mathrm{i}$ 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
• Correct answer
  C

  Move towards the wire
• D

  Remain stationary

Solution

Straight wire will produce a non-uniform field to the right of it. ${\overrightarrow{\text{F}}}_{\text{bc}}$ and ${\overrightarrow{\text{F}}}_{\text{ad}}$ will be calculated but integration of 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 the long 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.

Hence, the correct answer is option: 'C'.