A ring of radius R, made of an insulating material, carries a charge Q uniformly distributed on it. If the ring rotates about the axis passing through its centre and normal to plane of the ring with constant angular speed $\omega$, then the magnitude of the magnetic moment of the ring is

• A

  ${\mathrm{Q\omega R}}^2$

• B

  $\frac{1}{2}{\mathrm{Q\omega R}}^2$

• C

  ${\mathrm{Q\omega }}^{2}R$

• D

  $\frac{1}{2}{\mathrm{Q\omega }}^{2}R$