# Compton vs photoelectric effect.

• A Dhingra
In summary, the photoelectric effect and Compton scattering both involve the interaction of one photon and one electron, but with different energies of the photon. The photoelectric effect occurs when the electron is bound to something else, such as an atom or in a solid, and absorbs the photon's energy, converting it to kinetic energy. Compton scattering, on the other hand, occurs when the electron is free and cannot completely absorb the photon, causing it to scatter and transfer excess momentum. The electron is able to determine whether to absorb or scatter the photon based on the energy of the photon and its own binding energy.

#### A Dhingra

hi...
i found a number of similar thread posing the same question but i didn't get the answer i was looking for, so i am asking it again.

Basically, as far as i have understood photoelectric effect is about absorption of a photon by an electron and the extra energy converted to its kinetic energy; while in case of Compton effect there is collision (or scattering), not complete absorbtion, and the recoil.
The two are about interaction of one photon-and-one electron, but with different energies of the photon, still in one, electron completely absorbs the photon and gets kinetic energy; while the other doesn't convert the whole energy to kinetic energy instead produces a photon of greater wavelength. How really is the electron able to decide when to absorb a photon and when to scatter it; how does the electron get to know the energy of the photon before interacting with it (i.e. absorbing); does it sense the energy and decides what to do next with it??
What really happens??
(please pardon me if the questions sound stupid and irrelevant).

You can only have photoelectric effect if the electron is already in some potential. Say your electron is in some metal and you shine light on it to make it jump off - this is photoelectric effect.

Compton scattering is scattering photons off free electrons.

If the electron is free, it cannot completely absorb the photon, because there is no final configuration with a single electron and no photon that conserves both energy and momentum. So a free electron can only undergo Compton scattering. The photoelectric effect requires that the electron be bound to something else (an atom or in a solid) so it can transfer the excess momentum.

phyzguy said:
If the electron is free, it cannot completely absorb the photon, because there is no final configuration with a single electron and no photon that conserves both energy and momentum. .
I agree to this.
phyzguy said:
So a free electron can only undergo Compton scattering. The photoelectric effect requires that the electron be bound to something else (an atom or in a solid) so it can transfer the excess momentum.
But Compton scattering can be observed by electrons of carbon atom, then why not for metals? Like photoelectric effect...

A Dhingra said:
I agree to this.

But Compton scattering can be observed by electrons of carbon atom, then why not for metals? Like photoelectric effect...

If the energy of the incident photon is very large compared to the binding energy (a free electron is of course just an extreme case of this) you get Compton scattering.

If the energy of the incident photon is greater than than the binding energy, but not enormously so, you get the photoelectric effect.

## 1. What is the difference between Compton and photoelectric effect?

The Compton effect is the scattering of photons by particles, resulting in a change in wavelength and energy of the photons. The photoelectric effect, on the other hand, is the emission of electrons from a material when it is exposed to electromagnetic radiation. In short, the Compton effect involves the interaction of photons with particles, while the photoelectric effect involves the interaction of photons with electrons.

## 2. Can you explain the equations for Compton and photoelectric effect?

The Compton effect is described by the equation Δλ = h/mc (1 - cosθ), where Δλ is the change in wavelength, h is Planck's constant, m is the mass of the particle, c is the speed of light, and θ is the angle of scattering. The photoelectric effect is described by the equation E = hf - φ, where E is the energy of the emitted electron, h is Planck's constant, f is the frequency of the incident photon, and φ is the work function of the material.

## 3. Which effect is responsible for the production of X-rays?

The Compton effect is responsible for the production of X-rays. When high energy photons, such as those in the X-ray range, interact with particles, they can undergo the Compton effect, resulting in a change in wavelength and energy. This change in energy can produce X-rays.

## 4. How do the Compton and photoelectric effect relate to each other?

The Compton effect and photoelectric effect are both examples of how electromagnetic radiation interacts with matter. They are related in that they both involve the interaction of photons with matter, but they have different outcomes. The Compton effect results in a change in wavelength and energy of the photons, while the photoelectric effect results in the emission of electrons from the material.

## 5. In what scenarios would you observe the Compton effect and photoelectric effect?

The Compton effect is commonly observed in high energy interactions, such as in particle accelerators or the production of X-rays. The photoelectric effect is commonly observed in low energy interactions, such as in solar panels or the production of electricity in photocells. However, both effects can occur in various scenarios, as long as there is interaction between photons and matter.