Let the radius of ring be r and thickness of the ring be dr The expression for the charge on the element is written as, dq=σ(2πr)dr The current associated with the rotatingcharge dq is calculated as
di=
dq
T
=
dqω
2π
This implies that, di=σωrdr The expression for the magnetic field at the centre is calculated as
dB=
µ0di
2r
=
µ0σωrdr
2r
=
µ0σωrd
2
Integratethe expression to calculate the net magnetic field as, Bnet=