A square loop ABCD carrying a current i, is placed near and coplanar with a long straight conductor XY carrying a current I, the net force on the loop will be :

 Force on arm AB due to current in conductor XY is acting towards XY in the plane of loop and is equal to,

${\mathrm{F}}_1=\frac{{\mathrm{\mu }}_0}{4\mathrm{\pi }}\frac{2\mathrm{IiL}}{(\mathrm{L}/2)}=\frac{{\mathrm{\mu }}_0\mathrm{Ii}}{\mathrm{\pi }}$ 

Force on arm CD due to current in conductor XY is acting away from XY in the plane of loop and is equal to,

${\mathrm{F}}_2=\frac{{\mathrm{\mu }}_0}{4\mathrm{\pi }}\frac{2\mathrm{IiL}}{3(\mathrm{L}/2)}=\frac{{\mathrm{\mu }}_0\mathrm{Ii}}{3\mathrm{\pi }}$

Net force on the loop is, 

${\mathrm{F}}_{\mathrm{net}}={\mathrm{F}}_1-{\mathrm{F}}_2$

${\mathrm{F}}_{\mathrm{net}}=\frac{{\mathrm{\mu }}_0\mathrm{Ii}}{\mathrm{\pi }}\left[1-\frac{1}{3}\right]=\frac{2}{3}\frac{{\mathrm{\mu }}_0\mathrm{Ii}}{\mathrm{\pi }}$