Recently I got interested in the photoelectric effect and a little bit of quantum physics. So I have a couple of questions I'm really not in the clear about from the information I can find.

When I read the Wikipedia article https://en.wikipedia.org/wiki/Photoelectric_effect in the contents "Emission mechanism" there seems to be a lot of contrary statements which don't really make sense to me...

For one they say that the electrons follow some sort of "all or nothing" principle so that if the incoming photon doesn't have a high enough frequency, the photon gets reemitted again. But then they say that there is a time lag of at least $10^{-9}$ seconds between incidence & emission and that if you increase the intensity enough, there is still an emission regardless of it being a frequency less than the critical frequency!

I barely know anything about quantum physics for now, but it seems to me it's all about the absolute minimum "state" or "action" like electrons jumping from one orbit to another, but I don't really fully understand yet how photons as particles fit in this picture. Couldn't that all be more easily and intuitively explained by it being a continuous wave, and the apparent "photon" only happens because the non-light particles behave in some sort of quantized fashion? Like the double slit experiment would be so easily explained in that way without any "duality", but I digress...

So what exactly happens when a high intensity low frequency ray shines on metal, are there multiple photons on top of another or something?

  • 1
    $\begingroup$ Just a comment on your statement about double-slit experiment being easily explained by a continuous wave. First, it can be done with electrons interfering instead of photons, and electrons are clearly not continuous waves of matter. Also, the experiment can also be done such that only one photon is shot at a time, so single photons arrive at the detection screen, appearing as a point on the screen, so the continuous wave idea could not account for that. $\endgroup$
    – Hugo V
    Feb 6, 2019 at 13:43
  • $\begingroup$ Could you explain what seems contradictory to you in those statements? $\endgroup$
    – Hugo V
    Feb 6, 2019 at 13:49
  • $\begingroup$ thanks for the reply, first of all I'm fully aware that I don't know what I'm talking about so I appreciate any input . How is it clear that an electron is not a wave? and in the single photon case I mean more like the wave interacting with the particles in the screen and some just end up being in a more much more close to the next quantized state so thats the "photon" that one would see $\endgroup$
    – ctsmd
    Feb 6, 2019 at 13:53
  • $\begingroup$ The contradiction i see is within the "all or nothing" principle of electrons and the high intensity low frequency beam still resulting in an electron being given enough energy to fly out. $\endgroup$
    – ctsmd
    Feb 6, 2019 at 13:55
  • $\begingroup$ For your first comment I think the answer would have to me more elaborate, so I would suggest doing some research on elementary particles and why they are considered point particles, because if you are questioning if the eletron is a particle, you are actually questioning if there is such a thing as a particle in nature. Is that what you are saying, that you think there is no such thing as a particle? $\endgroup$
    – Hugo V
    Feb 6, 2019 at 14:08

1 Answer 1


The WP article simply doesn't seem very accurate, and some of the OP's statements summarizing it also seem like inaccurate descriptions of what the article says.

The article says:

Electrons can absorb energy from photons when irradiated, but they usually follow an "all or nothing" principle. All of the energy from one photon must be absorbed and used to liberate one electron from atomic binding, or else the energy is re-emitted.

This is wrong on several counts. If it were true, then there would be no such thing as absorption of red or infrared light by matter, which is false. It also makes it sound like electrons are bound to atoms. This would be true, for example, in a gas, but in real-world experiments using the photoelectric effect, we usually use metals as the cathode, so there are conduction electrons available, which are not bound to any atom. The threshold for the photoelectric effect occurs because of the energy required for the electron to escape through the surface of the metal.

The OP says:

they say that there is a time lag of atleast 10^-9 seconds between incidence & emission

But the article says:

The time lag between the incidence of radiation and the emission of a photoelectron is very small, less than 10−9 second.

These are opposite statements.

The OP says:

if you increase the intensity enough there is still an emission regardless of it being a frequency less than the critical frequency

But this is not true in reality, and I don't see anything in the WP article that says this.


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