Question

The line spectrum of lithium has a red line at 670.8 nm. Calculate the energy of a photon with this wavelength.

Answer 1

First of all, we can calculate the frequency of the photon, which is related to the wavelength by the following equation:

`f= (c)/(\lambda)`
where c is the speed of light and
`\lambda=670.8 nm=670.8 \cdot 10^(-9) m` is the photon wavelength. Substituting into the formula, we find the frequency

`f= (c)/(\lambda)= (3 \cdot 10^8 m/s)/(670.8 \cdot 10^(-9) m)=4.47 \cdot 10^(14) Hz`

Now we can find the energy of the photon with the following equation:

`E=hf`
where h is the Planck constant. Substituting numbers, we find

`E=hf=(6.6 \cdot 10^(-34)Js)(4.47 \cdot 10^(14) Hz)=2.95 \cdot 10^(-19) J`