Question

The wavelength of a red night lamp that I use in my house (not that I am scared of monsters under my bed, it is just a habit) is 700 nm. Find the energy contained in each photon of light.

• A. 4.77 eV
• B. 3.77 eV
• C. 2.77 eV
• D. 1.77 eV.

Answer 1

The correct option is D

1.77 eV.

The energy carried by a photon is given by the quantum relation E=hν, or interchangeably, E$=\frac{hc}{\lambda }$. Remember that the photon itself does not have any frequency or wavelength - it is not a wave. It just so happens that the photon's energy is related to the frequency of the light wave it corresponds to.

Anyway, the energy contained in a photon of light of wavelength 700nm will be -

$E=\frac{hc}{\lambda }=\frac{(6.626\times {10}^{-34}js)\times (3\times {10}^{3}m/s)}{700\times {10}^{-9}m}=2.839\times {10}^{-19}J=(2.839\times {10}^{-19}\times 6.2415\times {10}^{18})ev=1.772eV$