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- Thread starter curiousatlarg
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Drakkith

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What amplitude are you referring to?

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More here:

http://en.wikipedia.org/wiki/Photoelectric_effect

Photoelectric effect

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Physics Monkey

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I assume by amplitude you mean the magnitude of the electric field, let's call it E. In fact, E is related to the average number of photons via [itex] N \sim E^2[/itex]. Please note also the very important word average. A macroscopic electric field does not correspond to an exact number of photons but instead to something called a coherent state of photons (we can discuss this later if you want).

My claim above can be understood as follows. Let's think about a EM wave of fixed frequency. If you accept that the energy of one photon is [itex] h f [/itex] then the energy of N photons is [itex] N h f[/itex] and the rate of energy flow, which is proportional to the intensity, is [itex] I \sim c N h f[/itex] ([itex] c [/itex] is the speed of light i.e. how fast the photons are going). Now you also know that the intensity is given by [itex] I \sim E^2 [/itex] in a classical EM wave, so by equating these two forms you find that [itex] E^2 \sim N[/itex] up to lots of factors that you can work out or look up somewhere.

Hope this helps.

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