How many photons are produced in a laser pulse of 0.727 J at 615 nm?

Answer 1

First we have to calculate the energy of a single photon of light with a wavelength of 615 nm.

We can use the equation

E = hc/λ

where E is energy, h is Planck's constant, c is the speed of light in a vacuum, and λ is the wavelength.

h = 6.626 x 10^-34 J·s

c = 3.00 x 10⁸ m/s

Note that our units have to be consistent. Because c has units of m/s, we should convert the wavelength into meters. 615 nm = 6.15 x 10^-7 m.

So the energy of one photon is

E = (6.626 x 10^-34 J·s)(3.00x10⁸m/s) / (6.15 x 10^-7 m) = 3.23 x 10^-19J

So we have 3.23 x 10^-19 Joules per photon.

If we take 0.727 J and divide by 3.23 x 10^-19 Joules per photon then we get 2.25 x 10¹⁸ photons.