Question

How many photons are produced in a laser pulse of 0.459 J at 637 nm?

Answer 1

The relationship between energy of a single photon and its wavelength is given as:

E = h c / λ
E = energy per photon
h = Plancks constant = 6.626x10^-34 J s
c = speed of light = 3.00x10⁸ m/s
λ = wavelength = 637 nm = 637 x10^-9 m

If you can find the energy of a single wavelength of 637 x10^-9 m, you can then determine the number of photons that gives total 0.459 J energy.

Then, from above equation:

E = (6.626x10^-34)(3 x 10⁸) / 637 x10^-9

E = 3.12 x 10^-19 J

This is the energy in Joules for a single photon.

Now, the number of photons in 0.459 J = 0.459 / 3.12 x 10^-19

Number of photons in 0.861 J = 1.47 x 10¹⁸ photons.