Question

The wave number of the $H_{\alpha }$ - line in Balmer series of hydrogen spectrum is :

• A. 5R / 36
• B. 3R
• C. 21R / 100
• D. 3R / 4

Answer 1

The correct option is A 5R / 36

Wave number is reciprocal of wavelength i.e. number of wavelength per centimeter. It is denoted by $\overline{\nu }$. H-alpha ($H_{\alpha }$) is a specific deep-red visible spectral line in the Balmer series with a wavelength of 656.28 nm; it occurs when a hydrogen electron falls from its third to second lowest energy level. For $H_{\alpha }$ - line in Balmer series of hydrogen spectrum $\overline{\nu }$ is given by $\overline{\nu }=R[\frac{1}{2^2}-\frac{1}{3^2}]$ = $\frac{5R}{36}$, where $R$ is Rydberg constant.