Question

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

Answer: (A), (C)

We see the following:
- $F_{BC}$ is perpendicular plane of the loop and it acts in the upward direction.
- $F_{DA}$ is perpendicular of the loop and it acts in the downward direction. Therefore, the net force on the loop is zero.
$F_{AB}=F_{CD}=0$
Now, $\vec{J}=I\vec{A}\times \vec{B}$
$|\vec{J}|=\mid AB\sin \theta |$
Here, $\theta =90^{\circ },|\vec{J}|=\mid AB\ne 0|$.
As seen from the point $O$, the loop rotates in clockwise direction.