Question

Every series of hydrogen spectrum has an upper and lower limit in wavelength . The spectral series which has an upper limit of wavelength equal to $18752\mathring{A}$ , is

• A. Balmer series
• B. Lyman series
• C. Paschen series
• D. pfund series

Answer 1

The correct option is C Paschen series

For hydrogen spectrum from Bohr's theory
$\frac{1}{\lambda }=R(\frac{1}{n_1^2}-\frac{1}{n_2^2})$
$(\frac{1}{n_1^2}-\frac{1}{n_2^2})=\frac{1}{\lambda R}$
$=\frac{1}{18752\times {10}^{-10}\times 1.097\times {10}^7}$
$=\frac{486}{10000}=\frac{7}{144}$
$=\frac{4^2-3^2}{3^2\times 4^2}$
$=(\frac{1}{3^2}-\frac{1}{4^2})$
$Rightarrow$ ${\pi }_1=3,{\pi }_2=4$
It is true for Paschen series.