Modern Physics 1 Question 36

33. The wavelength of light emitted in the visible region by He+ions after collisions with H atoms is

(a) 6.5×107m

(b) 5.6×107m

(c) 4.8×107m

(d) 4.0×107m

(2008, 4M)

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Solution:

  1. Visible light lies in the range, λ1=4000\AA to λ2=7000\AA. Energy of photons corresponding to these wavelengths (in eV ) would be :

E1=123754000=3.09eVE2=123757000=1.77eV

From energy level diagram of He+atom, we can see that in transition from n=4 to n=3, energy of photon released will lie between E1 and E2.

ΔE43=3.4(6.04)=2.64eV

Wavelength of photon corresponding to this energy,

λ=123752.64\AA=4687.5\AA=4.68×107m



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