# The recoil of an electron receding from a photon

• Akihiro
In summary, the frequency of a photon is frame-dependent and can have different energies depending on who is observing it. If an electron moves in the same direction as the photon, it will recoil as if struck by a photon with a lower frequency, which is consistent with the conservation of energy. The effective frequency of the photon can be calculated using the formula f'=fm/(E+p) in the rest system of the electron.
Akihiro
Hi, everyone, I'm a high school student and i want to ask if an electron moves in the same direction as the photon which is about to strike it, would it recoil away as if struck by one with a lower frequency (due to Dopler's effect/ red-shifting effect) or would it recoil as if struck by the photon of original frequency without any alteration?

It would "recoil" as if struck by one with a lower frequency. "Frequency" is the same as energy for photons, and energy is frame-dependent. Depending upon who's looking at it, the photon can have different energies.

- Warren

Yes, the effective frequency of the photon will be less.
It is given by f'=fm/(E+p) for an electron of mass m, momentum p,
and total energy E.

chroot said:
It would "recoil" as if struck by one with a lower frequency. "Frequency" is the same as energy for photons, and energy is frame-dependent. Depending upon who's looking at it, the photon can have different energies.

- Warren

Thx for the reply. And just to add, would this suggest a violation of conservation of energy??

It is consistent with conservation of energy. Energy is a four-vector in SR, and is usually different in different systems (as Chroot said). The f' in my answer above is the frequency of the photon in the rest system of the electron.

## 1. What is the recoil of an electron receding from a photon?

The recoil of an electron receding from a photon refers to the motion or momentum change of the electron when it absorbs or emits a photon. This phenomenon is a result of the conservation of energy and momentum.

## 2. How does the recoil of an electron affect its trajectory?

When an electron recedes from a photon, its trajectory will change due to the momentum transfer. The direction and speed of the electron will be affected by the properties of the photon, such as its energy and angle of incidence.

## 3. Can the recoil of an electron be observed in experiments?

Yes, the recoil of an electron can be observed in various experiments, such as Compton scattering and photoelectric effect. These experiments involve the interaction between photons and electrons, allowing scientists to study the recoil effect.

## 4. How does the recoil of an electron relate to the concept of wave-particle duality?

The recoil of an electron is a result of the wave-particle duality of light. This concept states that light can behave as both a wave and a particle, and the recoil effect demonstrates the particle-like behavior of photons.

## 5. Does the recoil of an electron have any practical applications?

Yes, the recoil of an electron has practical applications in various fields, such as astronomy, physics, and technology. It allows scientists to study the properties of light and electrons, and it is also utilized in devices like lasers and solar cells.

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