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 $6\to 5$
Minimum wavelength is given by
$\frac{1}{{\lambda }_{\min }}=R\left(\frac{1}{5^2}-\frac{1}{\infty }\right)$
In transition $\infty \to 5$
So, ratio is $\frac{36}{11}$.