Q.

A circular loop of radius r is carrying current 1 A. The ratio of magnetic field at the center of the circular loop and at a distance r from the center of the loop on its axis is     [2023]
 

1 1:32  
2 22:1  
3 32:2  
4 1:2  

Ans.

(2)

Magnetic field due to a current carrying circular loop on its axis is given as

B=μ0ir22(r2+x2)3/2

At centre, x=0, B1=μ0i2r

At x=r, B2=μ0i2×22r

B1B2=22