Modern Physics 4 Question 1

1. Consider an electron in a hydrogen atom, revolving in its second excited state (having radius 4.65\AA ). The de-Broglie wavelength of this electron is

(Main 2019, 12 April II)

(a) 3.5\AA

(b) 6.6\AA

(c) 12.9\AA

(d) 9.7\AA

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Solution:

  1. By Bohr’s IInd postulate, for revolving electron,

 Angular momentum =nh2πmvrn=nh2π Momentum of electron, p=mv=nh2πrn

de-Broglie wavelength associated with electron is

λn=hp=2πrnn Given, n=3,rn=4.65\AAλn=(2×π×4.65)39.7\AA



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