The figure below represents the one vertex of square loop at origin,
For wire AB , magnetic filed, B0(1+0)=B0x=0 For wire CD, magnetic filed, B0(1+Ly)x=L For wire BC, magnetic filed, B0(1+Lx)y=L For wire AD, magnetic filed, B0y=0 The forces in the square loop, F1=0∫LIB0=IB0LF2=0∫LIB0(1+Lx)dx=23IB0LF3=0∫LIB0(1+Lx)dx=23IB0LF4=0∫LIB0dx=IB0L The force in x direction, Fx=F3−F1Fx=23IB0L−IB0LFx=21IB0L Similarly, The force in y direction, Fy=F2−F4Fy=23IB0L−IB0LFy=21IB0L The net magnitude of force, F=(21IB0L)2+(21IB0L)2F=2IB0L