Question

Directions: The following question has four choices, out of which one or more are correct. An infinite current-carrying wire passes through point O and in perpendicular to the plane containing a current-carrying loop ABCD as shown in the figure. Choose the correct option(s).

• (A) Net force on the loop is zero.
• (B) Net torque on the loop is zero.
• (C) As seen from O, the loop rotates clockwise.
• (D) As seen from O, the loop rotates anticlockwise.

Answer 1

The Correct Option is A, D

Explanation:
Force acting on the section $BC$ due to the magnetic field is $F_{BC}$. It is perpendicular to the plane of the loop and it acts in the upward direction. Force acting on the section DA due to the magnetic field is $F_{DA}$. It is perpendicular to the loop and it acts in the downward direction. Therefore, the net force on the loop is zero. $F_{AB}=F_{CD}=0$As the current in the loop is clockwise, therefore the magnetic moment associated with it is in downward direction. Hence, the torque due to the magnetic field is

$$\overrightarrow{\tau }=\overrightarrow{M}\times \overrightarrow{B}$$Hence torque acting on the loop is clock wise as seen from point $O.$