# Experiment involving photoelectric effect

• math_04
In summary, the conversation is about the possibility of seeing an interference pattern on a shiny metal surface when light is shined through two slits, and whether this would still support the particle theory of light. There is also a discussion about the photoelectric effect and how it relates to the wave-particle duality of light. Some participants suggest reading a paper on the subject and clarify that quantum mechanics has a unified description of light, while others argue that the term "particle" may not be the most accurate way to describe light.
math_04
Reading through the lecture notes, I had a weird idea which came in the form of an experiment that could be done.

Imagine you shine light through two slits. Obviously you will get an interference pattern with bright and dark lines (constructive and destructive interference). Then on the other side of the slit, you have a shiny metal surface where you view the interference pattern. Not sure about this but would you be able to see an interference pattern on a shiny metal surface? The question is if you could, would you still be able to say that the particle theory of light (photoelectric effect), which states that light is composed of individual packets called photons which each carry a certain energy E= hf, holds true?

When you try and detect the current flowing through the metal, i am guessing that current still flows otherwise by now quantum theory would be in a big mess haha. But I fail to understand how they could get out of this experiment. Anyone care to explain?

Cheers

Current in metal no good when interfere because lines too close. Need heat to get electrons off metal.

math_04 said:
Reading through the lecture notes, I had a weird idea which came in the form of an experiment that could be done.

Imagine you shine light through two slits. Obviously you will get an interference pattern with bright and dark lines (constructive and destructive interference). Then on the other side of the slit, you have a shiny metal surface where you view the interference pattern. Not sure about this but would you be able to see an interference pattern on a shiny metal surface? The question is if you could, would you still be able to say that the particle theory of light (photoelectric effect), which states that light is composed of individual packets called photons which each carry a certain energy E= hf, holds true?

When you try and detect the current flowing through the metal, i am guessing that current still flows otherwise by now quantum theory would be in a big mess haha. But I fail to understand how they could get out of this experiment. Anyone care to explain?

Cheers

I am not sure what you are trying to get at here. Why would you want to "view" the interference effect using the photoelectric effect? Just to show that light can still have particle properties? Just because this light came from a 2-slit experiment makes no difference. It is still a light, and you can do to it the same thing you can do to any light. How were you to know the intricate history of the light that was used to go through the 2-slit in the first place? Would that make any difference if I used a synchrotron source, or an arc lamp? Those two used completely different principles to generate light.

Please note that the spectrum of photoelectrons emitted from a photoemission process isn't trivial, and the emitted electrons can go in many different directions. You cannot "view" this the same way you view those interference pattern.

Zz.

I am suggesting that if the wave theory of light explains the interference pattern and you do what I have told above, why does the classical theory of light not work. In other words, an increasing intensity of light should increase the current flow but it does not. I used the double slit in forcing light to be a wave and hit the metal as a wave or does it somehow change back into particle form?

I thought light interacts as a wave in some situations and as a particle in others?

math_04 said:
I am suggesting that if the wave theory of light explains the interference pattern and you do what I have told above, why does the classical theory of light not work. In other words, an increasing intensity of light should increase the current flow but it does not. I used the double slit in forcing light to be a wave and hit the metal as a wave or does it somehow change back into particle form?

I thought light interacts as a wave in some situations and as a particle in others?

Er... there is only ONE description of light within the QM formalism. Read the FAQ in the General Physics forum. Using the particle picture, one can also arrive at the interference pattern.

"wave theory" IS the classical theory of light. And increasing the intensity DOES increase the current flow in a photoelectric effect - you get more electrons out since there are more photons per unit time per unit area.

I think there's a serious misunderstanding of not only the photoelectric effect, but basic quantum physics here.

Zz.

Oh so there is only one unified description of light according to quantum mechanics. I get that but how does quantum mechanics achieve that at least through the Schrodinger equation. How do you unify something that displays both wave like nature and particle like behaviour?

math_04 said:
Oh so there is only one unified description of light according to quantum mechanics. I get that but how does quantum mechanics achieve that at least through the Schrodinger equation. How do you unify something that displays both wave like nature and particle like behaviour?

Read the Marcella paper that I've mentioned several times on here. He derived all the interferences effects not using waves, but purely using QM.

http://arxiv.org/ftp/quant-ph/papers/0703/0703126.pdf

Zz.

math_04 said:
How do you unify something that displays both wave like nature and particle like behaviour?

That's just what standard quantum mechanics does. However, a lot of physicists do object to the term "particle" for light, and prefer instead to talk about energy quanta or packets of energy.

There is a difference between saying that the amount of energy is present in discrete units (integer multiples of hf), vs. calling something a particle.

math_04 said:
I thought light interacts as a wave in some situations and as a particle in others?

My understanding is that it behaves as both, all the time. (But see my comment above on using the term "particle".)

## 1. What is the photoelectric effect?

The photoelectric effect is a phenomenon in which electrons are emitted from a material when light of a certain frequency or higher is shone upon it. This effect was first observed by Heinrich Hertz in 1887 and was later explained by Albert Einstein in 1905 through his theory of the quantization of light.

## 2. How does the photoelectric effect work?

When light of a certain frequency, known as the threshold frequency, is shone onto a material, it causes the electrons within the material to absorb the energy from the photons in the light. If the energy of the photons is high enough, the electrons will be emitted from the material, creating a current. This process is known as the photoelectric effect.

## 3. What is the significance of the photoelectric effect?

The photoelectric effect has significant implications in the field of quantum mechanics and the understanding of the nature of light and matter. It also has practical applications in technology, such as solar cells and photomultiplier tubes, which use the photoelectric effect to convert light energy into electrical energy.

## 4. What factors affect the photoelectric effect?

The photoelectric effect is affected by several factors, including the frequency and intensity of the incident light, the type of material being used, and the work function of the material (the minimum amount of energy needed to remove an electron from the material). Additionally, the number of electrons emitted depends on the number of photons that hit the material and the efficiency of the material in converting light energy into electron energy.

## 5. How is the photoelectric effect used in experiments?

The photoelectric effect is often used in experiments to study the properties of light and matter. Scientists can vary the frequency and intensity of the incident light to observe how it affects the emission of electrons from different materials. They can also measure the energy and velocity of the emitted electrons to further understand the behavior of electrons in the photoelectric effect.

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