Q.

Figure shows a current carrying square loop ABCD of edge length is 'a' lying in a plane. If the resistance of the ABC part is r and that of ADC part is 2r, then the magnitude of the resultant magnetic field at centre of the square loop is         [2025]

1 3πμ0I2a  
2 μ0I2πa  
3 2μ0I3πa  
4 2μ0I3πa  

Ans.

(3)

B→=B→AB+B→BC+B→CD+B→DA

B→AB=B→BC

          =μ0(2I/3)4π(a/2)[sin45°+sin45°](–k^)

          =μ0I23πa(–k^)

B→CD=B→DA

           =μ0(I/3)4π(a/2)[sin45°+sin45°](k^)

          =μ0I26πa(k^)

B→=2[μ0I23πa(–k^)+μ0I26πa(k^)]

⇒ B→=2μ0I3πa(–k^)