Amplitude of Electromagnetic wave?

[The_Thinker]

How come the energy of an electromagnetic wave depends only on its frequency?

Given by E = hf.

How come the energy depends only on the frequency of the wave and not on the magnitude of the E component of the wave?

Doesn't the energy depend on the amplitude? Or is there no such thing?

 

[Vanadium 50]

How come the energy of an electromagnetic wave depends only on its frequency?

It doesn't. It also depends on the amplitude. The equation you wrote was for a single photon.

 

[Renge Ishyo]

This was found with the photoelectric effect and interpreted by Einstein. It meant that electrons could not be ejected from a metal unless the light was above a certain frequency even if you made the light more "intense." (It used to be thought that energy was proportional to the intensity prior to this point). Changing the frequency of the light and not the intensity of the light caused the electrons to be ejected from the metal. It was later found that the intensity is proportional to the number of photons, not the energy.