What is the energy of the photon?

Question

An excited atom emits a photon of red light with a wavelength of 723. nm, what is the energy of the photon?

How do you do this problem?

Answer 1

well idk but it depends if a nanometer is a thousanth of a millameter??

Answer 2

For this, you have to use E = hf.

The frequency is:

f = c / λ = (3.00 x 10^8 m/s) / (723 x 10^-9 m) = 4.15 x 10^14 Hz

The energy of the photon is:

E = (6.63 x 10^-34 Js) x (4.15 x 10^14 Hz) = 2.75 x 10^-19 J