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If R is the Rydberg constant for hydrogen, what is the wave number of the first line of the Lyman series?
- 2R
- R/2
- 3R/4
- R/4
Correct answer: 3R/4
Solution
The Lyman series involves transitions from higher levels to n=1. The first line (lowest energy, longest wavelength) corresponds to the transition n=2 -> n=1. Wave number (1/lambda) = R_H*(1/n1² - 1/n2²) = R*(1/1² - 1/2²) = R*(1 - 1/4) = R*(3/4) = 3R/4.
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