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. If a steady current I is established in the wire, as shown in Fig., the loop

• 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

The correct option is C

move towards the wire

Referring to Fig. the forces acting on arms BC and AD are equal and opposite. The force on arm AB is given by
$F_1=\frac{{\mu }_{0}Ii}{2\pi a}$
which is directed towards the wire. The force on arm CD is given by
$F_2=\frac{{\mu }_{0}Ii}{2\pi (a+b)}$
which is directed away from the wire. Since $F_1>F_2$, the loop; will move towards the wire. Hence the correct choice is (c).