If an electron in a hydrogen atom jumps from the 3rd orbit to the 2nd orbit, it emits a photon of wavelength λ. When it jumps from the 4th orbit to the 3rd orbit, the corresponding wavelength of the photon will be

  1. \(\frac{{16}}{{25}}\lambda \)
  2. \(\frac{9}{{16}}\lambda \)
  3. \(\frac{{20}}{7}\lambda \)
  4. \(\frac{{20}}{{13}}\lambda \)

Answer (Detailed Solution Below)

Option 3 : \(\frac{{20}}{7}\lambda \)
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 When electron jumps from higher orbit to lower orbit then, wavelength of emitted photon is given by,

\(\frac{1}{\lambda } = R\left( {\frac{1}{{n_f^2}} - \frac{1}{{n_i^2}}} \right)\) 

So, \(\frac{1}{\lambda } = R\left( {\frac{1}{{{2^2}}} - \frac{1}{{{3^2}}}} \right) = \frac{{5R}}{{36}}\) 

and \(\frac{1}{{\lambda '}} = R\left( {\frac{1}{{{3^2}}} - \frac{1}{{{4^2}}}} \right) = \frac{{7R}}{{144}}\) 

∴ \(\lambda ' = \frac{{144}}{7} \times \frac{{5\lambda }}{{36}} = \frac{{20\lambda }}{7}\)

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