Question

The longest wavelength line in the Lyman series of the hydrogen spectrum is

• A. $949.8\mathring{A}$
• B. $972.6\mathring{A}$
• C. $1215.8\mathring{A}$
• D. $1025.8\mathring{A}$

Answer 1

Answer: (C)

$\frac{1}{\lambda }{R}_H\left[\frac{1}{n_1^2}-\frac{1}{n_2^2}\right]$
For longest wavelength in Lyman series,
$n_1=1,n_2=2$
$\frac{1}{\lambda }=1.09678\times 10^7\left[\frac{1}{(1{)}^2}-\frac{1}{(2{)}^2}\right]$
$\frac{1}{\lambda }=\frac{1.09678\times 10^7\times 3}{4}$
$\therefore \lambda =1.2156\times 10^{-7}m$
$=1215.6\mathring{A}$