Question

If R is the Rydberg’s constant for hydrogen the wave number of the first line in the Lyman series will be.

• A. $\frac{R}{4}$
• B. $\frac{3R}{4}$
• C. $\frac{R}{2}$
• D. 2R

Answer 1

Answer: (B)

$\frac{3R}{4}$

Answer 2

For Lyman series

$\bar{\nu} = \frac{1}{\lambda} = R\left( \frac{1}{1^{2}} - \frac{1}{n^{2}} \right)$

Here n = 2, 3, 4, 5.....

For first line

$\bar{\nu} = R\left( \frac{1}{1^{2}} - \frac{1}{2^{2}} \right) \Rightarrow \bar{\nu} = R\left( 1 - \frac{1}{4} \right) = \frac{3R}{4}$