According to the Bohr model, the orbital magnetic moment ($\mu$) of an electron is given by the product of the current ($I$) and the area of the orbit ($A$).

1. Current $I = \frac{e}{T} = \frac{ev}{2\pi r}$.
2. Area $A = \pi r^2$.
3. Thus, $\mu = \frac{evr}{2}$. From Bohr's postulates, the angular momentum $mvr = \frac{nh}{2\pi}$ . Substituting $vr = \frac{nh}{2\pi m}$ into the magnetic moment equation: $\mu = \frac{e}{2} \left( \frac{nh}{2\pi m} \right) = n \left( \frac{eh}{4\pi m} \right) = n \mu_B$. Therefore, $\mu \propto n$.