state any two postulates of bohr's theory of hydrogen atom. what is the maximum possible number of spectral lines observed when hydrogen atom is in its second excited state. justify your answer. calculate ratio of the maximum and minimum wavelength of the radiations emitted in this process.

1.Bohr's  Postulates are following :- He only used the principle of newtons mechanics and Planks theory in his postulates !!
1. In an atom, the electrons revolve around the nucleus in certain definite circular paths called orbits, or shells.
2. Each shell or orbit corresponds to a definite energy. Therefore, these circular orbits are also known as energy levels or energy shells.

2. Now hydrogen atom in second excited state means n=3
from where only only three types of spectral lines are observed!! 
3 to2, 2 to1, 3 to1.
The answer can be obtained by using  permutation and combination to find the answer if n is higher!
The required formulae is  n(n-1)/2 where n is the orbit no.  in which e is present!

3. Its a known fact that wavelength is inversely proportional to energy of photon emitted!
so by taking the inverse ratio of energies
the wavelength corresponding to maximum wavelength has minimum energy and vice versa!
maximum E = minimum wavelength = transition from n=3 to n=1
minimum E = maximum wavelength = transition from n=3 to n=2

As total energy of electron in nth orbit of H2 atom is given by :- E= -13.6n2eV.
Here, negative sign shows that the electron is bound to the nucleus and is not free to leave it.
Therefore,ratio of maximum  wavelength/ minimum wavelength = ratio of maximum energy / minimum energy.
                                                       =  13.6 (1/12  - 1/32) /13.6 (1/22 - 1/32)  
                                                       = 32/5

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