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 :

Question

( A ) $\sqrt{(F_3-F_1)^2+F{^2}{2}}$
( B ) $\sqrt{(F_3-F_1)^2-F{^2}{2}}$
( C ) $F_3$ – $F_1$ – $F_2$
( D ) $F_3$ – $F_1$ – $F_2$