I'm having a bit of trouble reconciling information taught about the wave theory of light and the predictions it makes about the photoelectric effect.

Let me first explain my understanding of the wave theory vs. particle theory of light in regards to the photoelectric effect.

In a classic photoelectric experiment, the wave theory of light predicts that the the incident light intensity varies the amplitude and energy of light while the particle theory of light predicts that the intensity of light determines the amount of incident photons.

In the context of the ejecting electrons, this means that the wave theory of light predicts that as light intensity increases, the KE of the electrons increases due to the increased energy of light but the amount of electrons ejected remains the same, as the light hits the same number of electrons. Conversely, in the particle theory of light, the amount of electrons increases with intensity, as there are more incident photons per unit area, but the KE of each electron remains the same, as the energy of the light does not change.

From this understanding, I expected that the wave theory of light would predict that the saturation current (maximum current) in a photoelectric effect would not vary with the intensity of light, as it only effects the energy of the electrons which is the stopping voltage. However, I was told that my understanding was incorrect and that the saturation current would increase alongside the intensity of light under the wave theory of light model.

Where did I go wrong in coming to the conclusion that the saturation current would not in fact vary with the intensity of light according the wave theory of light?

  • $\begingroup$ I’m not quite sure what your question is but I can understand your confusion For the wave theory of light. How can you discuss the saturation current of a wave in which itself cannot be described? It’s best to always consider a light wave as billions of individual photons. $\endgroup$ Apr 29, 2018 at 17:29
  • $\begingroup$ I might replace the word "always" with "in this case" $\endgroup$
    – garyp
    Feb 2, 2020 at 18:16

2 Answers 2


If you have constant frequency, and you increase the intensity, you will have more photons, more electrons will be removed from the material, so you will have a higher current.


This was one of the failure of wave theory: It couldn't explain the photoelectric effect because as per wave theory, intensity increases energy.

And because of this failure, Einstein came up with idea of considering light as having dual nature: behaving both like a wave as well as like a particle.

Einstein concluded that increasing intensity increases current because more photons would be released and consequently more electrons and more current.

Thus, when we talk about photoemission and Compton effect, we consider light as particle; but when we talk about diffraction, interference and polarization, we consider light as wave.

The answer is simple: Light has dual nature.


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