Atomic Structure - Result Question 93

####69. The atomic masses of He and Ne are 4 and 20amu, respectively. The value of the de-Broglie wavelength of He gas at 73C is ’ M ’ times that of the de-Broglie wavelength of Ne at 727C.M is

(2013 Adv.)

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Answer:

Correct Answer: 69. (4.14eV)

Solution:

  1. PLAN KE=12mv2=32RT

m2v2=2mKEmv=2mKE

λ (wavelength) =hmv=h2mKEh2m(T)

where, T= Temperature in Kelvin

λ(He at 73C=200K)=h2×4×200 λ(Ne at 727C=1000K)=h2×20×1000 λ(He)λ(Ne)=M=2×20×10002×4×200=5

Thus, M=5



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