Question

The ratio of energy of a photon of radiation of wavelength $2500\stackrel{\circ }{A}$ to that of a radiation of wavelength $7500\stackrel{\circ }{A}$ is:

• A. 9
• B. 3
• C. 7.5
• D. 2.5

Answer 1

The correct option is B 3

From Planck's quantum theory,

$E=\frac{hc}{\lambda }$
Given ,
${\lambda }_1=2500\stackrel{\circ }{A}$ and ${\lambda }_2=7500\stackrel{\circ }{A}$
$E\propto \frac{1}{\lambda }$
$\frac{E_1}{E_2}=\left(\frac{{\lambda }_2}{{\lambda }_1}\right)$
$\frac{E_1}{E_2}=\left(\frac{7500}{2500}\right)=3$