Question

The energy of photon of light wavelength $450nm$ is:

• A. $2.5\times 10^{-17}J$
• B. $1.25\times 10^{-17}J$
• C. $4.4\times 10^{-19}J$
• D. $2.5\times 10^{-19}J$

Answer 1

Answer: (C)

The energy of a photon is given by
$E=hv$
where, $h$ is Planck's constant and $v$ is frequency of light.
Also velocity $(c)=$ frequency $(v)\times$ wavelength $(\lambda )]$
$\Rightarrow v=\frac{c}{\lambda }$
where $c=3\times 10^{8}m/s,$
$\lambda =450nm$
$=450\times 10^{-9}m$
$\therefore E=\frac{6.6\times 10^{-34}\times 3\times 10^8}{450\times 10^{-9}}$
$E=4.4\times 10^{-19}J$