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Q.
What is the colour corresponding to the wavelength of light emitted when the electron in a hydrogen atom undergoes transition from $n = 4$ to $n = 2$?
Structure of Atom
Solution:
$\frac{1}{\lambda}=R\left[\frac{1}{n^{2}_{1}}-\frac{1}{n^{2}_{2}}\right]$
$=109677$
$\left[\frac{1}{2^{2}}-\frac{1}{4^{2}}\right]cm^{-1}$
$=205644.4\,cm^{-1}$
$\lambda=\frac{1}{20564.4\,cm^{-1}}$
$=486\times10^{-7}\,cm$ or $486\times10^{-9}\,m$
Colour corresponding to this wavelength is blue.