Q.

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    [2016]

1 2μ0IiL3π  
2 μ0IiL2π  
3 2μ0Ii3π  
4 μ0Ii2π  

Ans.

(3)

Force on arm AB due to current in conductor XY is

    F1=μ04π2IiL(L/2)=μ0Iiπ

acting towards XY in the plane of the loop.

Force on arm CD due to current in conductor XY is

      F2=μ04π2IiL3(L/2)=μ0Ii3π

acting away from XY in the plane of the loop.

  Net force on the loop=F1-F2=μ0Iiπ[1-13]=2μ0Ii3π