# Does Intensity actually effect the number of photons?

Does Intensity actually effect the number of photons?This question I ask because that's what I knew until I referred to the book by Dirac on quantum mechanics which says:" the wave function gives information about the probability of one Photon being in a particular place and not the probable number of photons in that place".

Does Intensity actually effect the number of photons?

Intensity is defined in classical electromagnetic field, including light.

Photons obey quantum mechanics as quantum mechanical elementary particles.

Photons carry the energy $$h*ν$$ where $$ν$$ is the frequency of the classical beam which is built up by very many photons and $$h$$ the Planck constant.

In quantum mechanics the wavefunction models the probability of finding a single photon at (x,y,z,t), so there is no problem with Dirac's statement.One needs many measurements of photons with the same condition to find this.

" the wave function gives information about the probability of one Photon being in a particular place and not the probable number of photons in that place".

To find the number of photons in a monochromatic pulse of classical light, one needs to know the energy in the pulse and divide it by the energy of the individual photon to find the number of photons.

See this answer of mine to get an intuition of how photons build up the classical wave of light.

• So does that mean the classical wave builder up by photons is different from the wave function associated with it? Jun 15 at 13:17
• ofcourse, they are solutions of different equations, the classical ,classical maxwell, the quantum quantized maxwell. Jun 15 at 13:37