The angular momentum of an electron in a Bohr's orbit of H-atom is $4.2178\times 10^{-34}Kg-m^2/s$.Calculate the spectral line emitted when electron falls from this level to next lower level.

Question

$\begin{array}{1 1}(a)\;1.8\times 10^{-2}cm&(b)\;1.8\times 10^{-4}cm\\(c)\;2.8\times 10^{-4}cm&(d)\;1.7\times 10^{-2}cm\end{array}$