Q.

An infinitely long straight wire carrying current I is bent in a planer shape as shown in the diagram. The radius of the circular part is r. The magnetic field at the centre O of the circular loop is :   [2026]

1 -μ02πIr(π-1)i^  
2 μ02πIr(π-1)i^  
3 -μ02πIr(π+1)i^  
4 μ02πIr(π+1)i^  

Ans.

(1)

B0=BAB+BDE+BBCD

=μ0i4πri^+μ0i4πri^-μ0i2ri^

=μ0i2πri^-μ0i2ri^

=μ0i2πr(1-π)i^

=-μ0i2πr(π-1)i^