Explanation:
FOR CLOSED CIRCUIT LOOP IN A UNIFORM MAGNETIC FIELD
total force F= [tex]I\oint\vec{ds}\times\vec{B}[/tex]
here vector B has constant strength and direction so, we take it outside the integral
F= [tex]I\times\vec{B}\oint\vec{ds}[/tex]
[tex]\oint\vec{ds}[/tex]= This vector displacements yields overall displacement
so, [tex]\oint\vec{ds}[/tex]=0
therefore,
F= [tex]I\times\vec{B}\oint\vec{ds}[/tex]=0
