Question

Write the statement of Bohr's Second postulate of quantisation. Determine the wavelength of first spectral line in the Lyman series of the hydrogen spectrum.[Rydberg constant R$=1.097\times {10}^7{m}^{-1}$].

Answer 1

Bohr's second postulate states that allowed electric motion are only in those orbits in which the angular momentum of an electron is an integral multiple of $\frac{h}{2\pi }$.

First spectral line of Lyman series of hydrogen atom is given by transition $(2\to 1)$

$\frac{1}{\lambda }=R(\frac{1}{n_1^2}-\frac{1}{n_2^2})$

$=1.097\times {10}^7(\frac{1}{1^2}-\frac{1}{2^2})m^{-1}$

$=8227500m^{-1}$

$⟹\lambda =121.5nm$