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When light acts as a particle/photon as in the photoelectric effect, the intensity does refer to the amount of photons. The significance is that there is a 1:1 ratio between photons and ejected electrons (with sufficient frequency). So, if we double the intensity of the light, we'll have twice as many electrons ejected. But, if the light is of insufficient frequency, increasing the intensity will have no effect.
Emma Leshan wrote:Continuing off that note, when light acts as a wave, or for any wave, the intensity relates to the amplitude/height of the wave.
Specifically, I think in one part of the textbook it referenced that in terms of the wave model intensity is proportional to the square of amplitude to the wave.
It also referenced that for the particle model, intensity was "proportional to the number of photons in an instant".
The intensity of light is the amount of photons. That is why making a light more intense will not result in an electron being removed from an atom. Each individual photon needs enough energy to remove and electron.
When the energy of the photon is equal or greater than the threshold energy, then an electron can be ejected. By increasing intensity, you are increasing photons, so if and only if we can meet the threshold energy can increasing intensity result in more electrons being ejected.