Modern Physics 1 Question 18

15. The largest wavelength in the ultraviolet region of the hydrogen spectrum is 122nm. The smallest wavelength in the infrared region of the hydrogen spectrum (to the nearest integer) is

(a) 802nm

(b) 823nm

(c) 1882nm

(d) 1648nm

(2007,3 M)

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Solution:

  1. The series in UV region is Lymen series. Longest wavelength corresponds to minimum energy which occurs in transition from n=2 to n=1.

122=1R112122

The smallest wavelength in the infrared region corresponds to maximum energy of Paschen series.

λ=1R1321

Solving Eqs. (i) and (ii), we get

λ=823.5nm



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