In a hydrogen atom, an electron of mass m and charge e is in an orbit of radius r making n revolutions per second. If the mass of the hydrogen nucleus is M, the magnetic moment associated with the orbital motion of the electron is:

The charge crossing any point of the path per second, is n times the charge e of the electron. This constitutes the current around the orbit, i.e. I = ne. If A is the area of the orbit, the magnetic moment is given by the product:

$\mathrm{IA} = {\mathrm{ne\pi r}}^2$