Question

The first spectral line in the Pfund series of Hydrogen spectrum is given by ($R_H$ = Rydberg constant) :

• A. $\frac{56R_H}{36}$
• B. $\frac{7R_H}{144}$
• C. $\frac{11R_H}{900}$
• D. $\frac{9R_H}{400}$

Answer 1

Answer: (C)

$\frac{11R_H}{900}$

A series of wavenumber in the Pfund series of the Hydrogen spectrum is given by $R_H[\frac{1}{5^2}-\frac{1}{n^2}]$, where $R_H$ is the Rydberg constant for hydrogen and n is an integer greater than 5.

Now, first spectral line $n=6$.

$\frac{1}{\lambda }=R_H[\frac{1}{5^2}-\frac{1}{6^2}]=R_H[\frac{1}{25}-\frac{1}{36}]=\frac{11R_H}{900}$.