Question

In Pfund series, ratio of maximum to minimum wavelength of emitted spectral lines is

• A. $\frac{\lambda_{\max }}{\lambda_{\min }}=\frac{4}{3}$
• B. $\frac{\lambda_{\max }}{\lambda_{\min }}=\frac{9}{5}$
• C. $\frac{\lambda_{\max }}{\lambda_{\min }}=\frac{16}{7}$
• D. $\frac{\lambda_{\max }}{\lambda_{\min }}=\frac{36}{11}$

Answer 1

Answer: (D)

In Pfund series,
$\frac{1}{\lambda}=R\left(\frac{1}{5^{2}}-\frac{1}{n^{2}}\right) ; n=6,7, \cdots$
Maximum wavelength is given by
$\frac{1}{\lambda_{\max }}=R\left(\frac{1}{5^{2}}-\frac{1}{6^{2}}\right)$
In transition $6 \rightarrow 5$
Minimum wavelength is given by
$\frac{1}{\lambda_{\min }}=R\left(\frac{1}{5^{2}}-\frac{1}{\infty}\right)$
In transition $\infty \rightarrow 5$
So, ratio is $\frac{36}{11}$.