Question

Hydrogen atom is excited by means of a monochromatic radiations of wavelength $975\mathring{A}$ . In emission spectrum the number of possible lines are :

• A. 2
• B. 4
• C. 5
• D. 6

Answer 1

Answer: (B)

Energy of radiations $E=\frac{hc}{\lambda }$
$=\frac{6.6\times 10^{-34}\times 3\times 10^8}{975\times 10^{-10}\times 1.6\times 10^{-19}}eV$
$=12.75eV$
Energy of hydrogen atom in first energy level $=-13.6eV$
Energy of atom after absorbing radiations
$=-13.6+12.75=-0.85eV$
Number of spectral lines
$E=\frac{13.6}{n^2}$
$n^2=\frac{13.6}{0.85}$
$n^2=16$
$\Rightarrow n=4$