Question

what is the energy (in eV units) carried by one photon violet light that has a wavelength of 4.5e-7?

Answer 1

The energy of a photon is given by

`E=hf`
where h is the Planck constant and f is the photon frequency.

We can find the photon's frequency by using the following relationship:

`f= (c)/(\lambda)`
where c is the speed of light and
`\lambda` is the photon's wavelength. By plugging numbers into the equation, we find

`f= (c)/(\lambda)= (3 \cdot 10^8 m/s)/(4.5 \cdot 10^(-7) m)=6.67 \cdot 10^(14)Hz`

And so now we can find the photon energy

`E=hf=(6.6 \cdot 10^(-34) Js)(6.67 \cdot 10^(14)Hz )=4.4 \cdot 10^(-19) J`

We know that 1 Joule corresponds to

`1 J = 1.6 \cdot 10^(-19) eV`
So we can convert the photon's energy into electronvolts:

`E= (4.4 \cdot 10^(-19) J )/(1.6 \cdot 10^(-19) J/eV)=2.75 eV`