A long wire carrying a steady current is bent into a circular loop of one turn. The magnetic field at the centre of the loop is B. It is then bent into a circular coil of n turns. The magnetic field at the centre of this coil of n turns will be?

The circumference of the first loop is the length of the wire=2πR
The magnetic field at the center of this wire=B=μ0I/2R
The same wire is bent into n circular coils.
Thus new radius is found out by
n×2πr=2πR
r=R/n
The magnetic field at the center of n turns coil is given by
B'=nμ0I/2r=nμ0I/(2R/n)=n2μ0I/2R=n2B