An electron of charge e moves in a circular orbit of radius r around a nucleus. The magnetic field due to orbital motion of the electron at the site of the nucleus is B. The angular velocity $\mathrm{\omega }$ of the electron is

• A

  $\frac{4\mathrm{\pi rB}}{{\mathrm{\mu }}_0\mathrm{e}}$

• B

  $\frac{2\mathrm{\pi rB}}{{\mathrm{\mu }}_0\mathrm{e}}$

• C

  $\frac{{\mathrm{\mu }}_0\mathrm{eB}}{\mathrm{\pi r}}$

• D

  $\frac{{\mathrm{\mu }}_0\mathrm{eB}}{4\mathrm{\pi r}}$