In Bohr model of hydrogen atom, find the ratio of period of revolution of the electron in the orbit n = 2 to that in the orbit n = 1.

$\displaystyle T=\frac{2 \pi r_{n}}{v_{n}}$ $\displaystyle r_{n} \propto n^{2}$ $\displaystyle v_{n} \propto \frac{1}{n}$ $\displaystyle T \propto n^{3}$ $\displaystyle \frac{T_{2}}{T_{1}}=\frac{\left(n_{2}\right)^{3}}{\left(n_{1}\right)^{3}}$ $\displaystyle =\frac{(2)^{3}}{(1)^{3}}$ $\displaystyle =\frac{8}{1}$