Momentum conservation in photoelectric effect

Click For Summary

Discussion Overview

The discussion revolves around the conservation of momentum in the context of the photoelectric effect, particularly examining whether momentum conservation is adequately addressed in the traditional photoelectric equation. Participants explore the implications of incorporating momentum conservation into the analysis of the photoelectric effect, including potential modifications to the equation and qualitative changes in the emitted electrons.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants assert that the traditional photoelectric equation focuses solely on energy conservation, neglecting momentum conservation, and question the justification for this approach.
  • Others argue that momentum conservation is indeed considered, suggesting that the momentum of the photon imparts an impulse to the electron, linking energy and momentum in this context.
  • A participant challenges the notion that energy and momentum can be treated as the same, seeking clarification on this point.
  • One participant emphasizes that in more advanced models, such as the Spicer 3-step model, both photon and electron momentum are explicitly accounted for, particularly in the in-plane direction.
  • It is noted that the lattice ions in a solid are necessary to absorb the recoil momentum of the emitted electrons, indicating that momentum conservation is context-dependent and varies between solids and gases.
  • Another participant mentions that the photoelectric effect results in the recoil of the nucleus, adding another layer to the discussion of momentum conservation.

Areas of Agreement / Disagreement

Participants express differing views on the treatment of momentum conservation in the photoelectric effect. While some believe it is neglected in the traditional equation, others contend that it is inherently considered in more complex models. The discussion remains unresolved regarding the extent to which momentum conservation is accounted for in the standard treatment of the photoelectric effect.

Contextual Notes

Participants highlight that the photoelectric effect occurs in solids, which introduces specific conditions regarding momentum conservation that may not apply in gaseous environments. The discussion reflects varying interpretations of the role of momentum in the photoelectric effect and the implications for the emitted electrons.

Who May Find This Useful

This discussion may be of interest to students and researchers in physics, particularly those studying quantum mechanics, the photoelectric effect, and the interplay between energy and momentum in particle interactions.

Reshma
Messages
749
Reaction score
6
The photoelectric equation is given by:
hf = hf0 + 1/2mv2 where f is the frequency of the incident wave and f0 is the threshold frequency.

HERE, only the conservation of energy is taken into consideration and momentum conservation is neglected. Why is this approach justified? Suppose we take momentum conservation into consideration--how will the photoelectric equation be modified?

What qualitative changes will be introduced in the emerging electron?
 
Physics news on Phys.org
see according to me definitely mommentum conservation has been taken into account,a photon having a definite momentum usese all its momentum to give an impulse to the the electron.infact momentum and energy here point to the same thing
 
That doesn't completely answer my question. How can you call the energy and momentum here as the same thing?
 
here the energy to the electron is provided by the momentum of the photon
 
Reshma said:
The photoelectric equation is given by:
hf = hf0 + 1/2mv2 where f is the frequency of the incident wave and f0 is the threshold frequency.

HERE, only the conservation of energy is taken into consideration and momentum conservation is neglected. Why is this approach justified? Suppose we take momentum conservation into consideration--how will the photoelectric equation be modified?

What qualitative changes will be introduced in the emerging electron?

No, conservation of momentum is not neglected if you go beyond the naive treatment of photoelectric/photoemission phenomenon.

Note one important thing: the photoelectric effect is the emission of electrons from a SOLID surface, such as a metal. This is crucial. In the Spicer 3-step model of photoemission, the momentum of both the photon and the outgoing electrons are explicitly considered. In this model, the in-plane momentum (momentum parallel to the surface of the cathode) is conserved. However, since the momentum of the photon is miniscule with respect to the in plane momentum of the outgoing electron, one doesn't detect the momentum of the photon by looking at the outgoing electron.

The perpendicular momentum is something else. The existence of the solid, or more specifically, the lattice ions, is NECESSARY to take up the recoil momentum of the outgoing electrons (this means that photoemission as we know it doesn't occur in gasses - photoIONIZATION that occurs in gasses are of a different nature). Furthermore, since the electrons can come out from different energy within a band, there are no conservation of energy and momentum in the perpendicular direction.

So yes, these considerations ARE already studied and taken care of in a photoemission phenomenon.

Zz.
 
  • Like
Likes   Reactions: jaysriramroy
The photoelectric effect causes the nucleus to recoil
 
Thank you very much, ZapperZ. I completely got it now.
 
Hello! thanks for the information.
could you please suggest me a book or some other resource regarding this? I need more.
many thanks!
 

Similar threads

  • · Replies 5 ·
Replies
5
Views
1K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 35 ·
2
Replies
35
Views
4K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 13 ·
Replies
13
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 8 ·
Replies
8
Views
3K