Energy of a Wave & the Photoelectric Effect: Is My Statement Correct?

[Sandeep T S]

In classical electrodynamics energy of a wave is proportional to its intensity , this theory fails when Hertz did experiment on photoelectric effect. Is my statement is correct? If not correct me.

 

[PeterDonis]

In classical electrodynamics energy of a wave is proportional to its intensity

What do you mean by "intensity"? The correct mathematical statement is that the energy of a classical EM wave is proportional to the square of its amplitude.

this theory fails when Hertz did experiment on photoelectric effect

What theory? Classical electrodynamics? Yes, the observed photoelectric effect cannot be explained by classical electrodynamics. However, that has nothing to do with the classical formula for the energy carried by an EM wave.

 

[George Jones]

In classical electrodynamics energy of a wave is proportional to its intensity , this theory fails when Hertz did experiment on photoelectric effect. Is my statement is correct? If not correct me.

Quantization of the electromagnetic is consistent with the photoelectric effect, but it is not necessary to explain the photoelectric effect, i.e., the photoelectric effect can be explained by a classical electromagnetic radiation incident on a photomaterial. Of course, the photoelectric effect can be explained by quantized electromagnetic radiation incident on a photomaterial.

Both situations are treated quantitatively in the interesting book "Quantum Mechanics: Theory and Experiment" by Mark Beck.

 

[tech99]

Quantization of the electromagnetic is consistent with the photoelectric effect, but it is not necessary to explain the photoelectric effect, .

But I thought Einstein proposed quantisatiion to explain the effect. Why does intense white light not create electron emission?

 

[George Jones]

But I thought Einstein proposed quantisatiion to explain the effect. Why does intense white light not create electron emission?

This is explained in the text that I referenced, which probably is unavailable to you. See also the video below (between times 27:30 and 30:23), by Alain Aspect, who, in my opinion, should be a Nobel Laureate.

 

[king vitamin]

In classical electrodynamics energy of a wave is proportional to its intensity , this theory fails when Hertz did experiment on photoelectric effect. Is my statement is correct? If not correct me.

As George Jones already said, one may use a classical electromagnetic field in dealing with the photoelectric effect, and since the definition of intensity is independent of whether you treat the rest of the system as quantum or not, intensity is still proportional to the energy of an electromagnetic wave.

With that said, given the definition of intensity, I am fairly certain that even with a fully quantized electromagnetic field it would still be proportional to the (average/time averaged) energy of the field. But I'm happy to be corrected if I'm wrong on this point.

What do you mean by "intensity"? The correct mathematical statement is that the energy of a classical EM wave is proportional to the square of its amplitude.

Intensity is the power per unit area. For an electromagnetic wave. It is also proportional to the square of the amplitude of the electric field.

 

[tech99]

This is explained in the text that I referenced, which probably is unavailable to you. See also the video below (between times 27:30 and 30:23), by Alain Aspect, who, in my opinion, should be a Nobel Laureate.

Thank you very much for this fantastic lecture. Are we saying that the light source need not be quantised, but the wavelength must be ultra violet so that the wave energy exceeds the work function of the material?