Q.

Two identical long current carrying wires are bent into the shapes shown in the following figures. If the magnitude of magnetic fields at the centers P and Q of a semicircular arc are B1 and B2 respectively, then the ratio B1B2 is ______.               [2026]

1 2+π1+π  
2 1+π1-π  
3 2+π1-π  
4 1+π2-π  

Ans.

(1)

BP=μ0i4πr×2+μ0i4r=μ0i4r(1+2π)

BQ=μ0i4πr+μ0i4r=μ0i4r(1+1π)

⇒BPBQ=1+2/π1+1/π=π+2π+1