Q.

A long conducting wire having a current I flowing through it is bent into a circular coil of N turns. Then it is bent into a circular coil of n turns. The magnetic field is calculated at the centre of coils in both the cases. The ratio of the magnetic field in first case to that of second case is             [2023]

1 N:n  
2 n2:N2  
3 N2:n2  
4 n:N  

Ans.

(3)

l=(2πr)n

r(ln)

B=n(μ0i2r)(μ0i2L)n2

B1B2=(N2n2)