Question

Find the ratio of magnetic dipole moment and magnetic field at the centre of a disc. Radius of disc is R and it is rotating at constant angular speed o about its axis. The disc is insulating and uniformly charged

Answer 1

Answer:

Let surface charge density is σ.

(dq)=[(2πr)dr]σ

Equivalent current i=(dq)f

dM=iA=[(dq)f][πr2]

∴M=∫0RdM

dB=2rμoi=2rμo(dq)f

∴B=∫0RdB

Now, we can find the ratio BM