Question

The energy of photon of light wavelength $450\, nm$ 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
$E=h v$
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 , $
$\lambda=450\, nm$
$=450 \times 10^{-9} m $
$\therefore E=\frac{6.6 \times 10^{-34} \times 3 \times 10^{8}}{450 \times 10^{-9}} $
$E=4.4 \times 10^{-19} J$