(a) State Bohr's postulate to define stable orbits in hydrogen atom. How does de-Broglie's hypothesis explain the stability of these orbits ?
(b) A hydrogen atom initially in the ground state absorbs a photon which excites it to the p=4 level. Estimale the frequency of the pholon.

Explanation

(a) See Short Answer Question Number 29.
(b) We know that energy of an electron in a hydrogen atom is, `E = (13.6)/(n^(2)) eV`
For ground state n =1 , hence `E_(1) = - (13.6)/((1)^(2)) = - 13.6 eV`
and for excited state `n = 4` , hence `E_(2) = - (13.6)/((4)^(2)) = - 0.85 eV`
`therefore ` Energy gained by absorbing a photon of frequency y is given by
`E_(2) - E_(1) = (hv)/(e)`
`rArr " " v=(e)/(h) [E_(2) - E_(1)] = (1.6 xx 10^(-19))/(6.63 xx 10^(-34)) [(-0.85)] = (1.6 xx 10^(9) xx 12.75)/(6.63xx 10^(-34)) = 3.08 xx 10^(15) Hz`