Question

The ratio of energy of a photon of radiation of wavelength $2000\stackrel{\circ }{A}$ to that of a radiation of wavelength $4000\stackrel{\circ }{A}$ is:

• A. $\frac{1}{4}$
• B. $4$
• C. $\frac{1}{2}$
• D. $2$

Answer 1

The correct option is D $2$

From Planck's quantum theory,

$E=\frac{hc}{\lambda }$
Given ,
${\lambda }_1=2000\stackrel{\circ }{A}$ and ${\lambda }_2=4000\stackrel{\circ }{A}$
$E\propto \frac{1}{\lambda }$
$\frac{E_1}{E_2}=\frac{4000}{2000}\Rightarrow$ i.e., $\frac{{\lambda }_2}{{\lambda }_1}=2$