# A level physics Quantum

#1
Hi TSR,

I am just slightly confused on how the photoelectric effect shows that light has a particle-like nature. Could someone please explain this to me?

0
3 years ago
#2
Ok so for many years, light was thought of as a wave but this couldn’t explain the photoelectric effect. From experiments it was shown that if the light shone on the metal surface was below a particular frequency, no electrons would be emitted from the surface of the metal at all. Wave theory suggests that electrons would be emitted regardless of the frequency, but the rate of emissions would be lower the lower the frequency of light. Thinking of light as a particle explains the observation from the experiment. It is known that a metal has a work function (min energy of a photon incident on the metal surface for photoelectric emissions) the photon energy (hf) has to be equal to or above the work function. A photon transfers energy in a one on one interaction with an electron that allows the electron to leave the metal from the surface. If the photon energy isn’t at least equal to the work function, then no electrons are emitted from the surface of the metal. This therefore demonstrates the particle like nature of light. (Just finished my Physics A level 😂😂 hope this explanation helps)
2
3 years ago
#3
Ok so for many years, light was thought of as a wave but this couldn’t explain the photoelectric effect. From experiments it was shown that if the light shone on the metal surface was below a particular frequency, no electrons would be emitted from the surface of the metal at all. Wave theory suggests that electrons would be emitted regardless of the frequency, but the rate of emissions would be lower the lower the frequency of light. ....
There is a confusion between wave and particle model of light in the underlined statement.
According to wave theory of light, electrons should absorb energy continuously from the electromagnetic radiation. As the light intensity incident on a metal is increased, energy should be transferred into the metal at a higher rate and the electrons should be ejected with more kinetic energy.
Electrons should be ejected from the metal at any incident light frequency, as long as the light intensity is high enough, because energy is transferred to the metal regardless of the incident light frequency.

Both wave model and particle model of light suggest that the rate of emissions is dependent on the intensity.
0
3 years ago
#4
(Original post by Eimmanuel)
There is a confusion between wave and particle model of light in the underlined statement.
According to wave theory of light, electrons should absorb energy continuously from the electromagnetic radiation. As the light intensity incident on a metal is increased, energy should be transferred into the metal at a higher rate and the electrons should be ejected with more kinetic energy.
Electrons should be ejected from the metal at any incident light frequency, as long as the light intensity is high enough, because energy is transferred to the metal regardless of the incident light frequency.

Both wave model and particle model of light suggest that the rate of emissions is dependent on the intensity.
The intensity of the electromagnetic radiation can only affect the rate of photoelectric emissions if the frequency of the electromagnetic radiation is above a certain value (threshold frequency) as this will mean that the photon energy will be above a certain value (the metal’s work function) which provides evidence for light having particle-like properties.
0
3 years ago
#5
The intensity of the electromagnetic radiation can only affect the rate of photoelectric emissions if the frequency of the electromagnetic radiation is above a certain value (threshold frequency) as this will mean that the photon energy will be above a certain value (the metal’s work function) which provides evidence for light having particle-like properties.
My suggestion is reread what I underlined. What you have written here is different from what I have underlined in the previous post.
0
3 years ago
#6
(Original post by Eimmanuel)
My suggestion is reread what I underlined. What you have written here is different from what I have underlined in the previous post.
Sorry, I now realise that throughout the entirety of your post you were explaining how wave theory would explain the photoelectric effect which is why I was disagreeing with what you said. With the underlining I now see where I went wrong, thanks for your help, I didn’t mean to come off confrontational, I’m always looking to better my understanding of a subject, so thank you 🙏🏾
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