Question

A closed loop $PQRS$ carrying a current is placed in a uniform magnetic field. If the magnetic forces on segments $PS,SR$ and$RQ$ are $F_1,F_2$ and $F_3$ respectively and are in the plane of the paper and along the directions shown, the force on the segment $QP$ is

Answer 1

The net force on a current carrying loop placed in a magnetic field is zero.
Balancing the forces along horizontal and vertical direction we get,
$F_4\sin \theta =F_2$
$F_4\cos \theta =(F_3-F_1)$
$\therefore F_4=\sqrt{(F_3-F_1{)}^2+F_2^2}$
For a closed loop there is no translation.

Hence, option $\left(D\right)$ is correct.