Photoelectric Effect: Understanding Kinetic Energy of Electrons

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Discussion Overview

The discussion focuses on the photoelectric effect, specifically addressing the kinetic energy of ejected photo-electrons when light of the same frequency is incident on a metal surface. Participants explore the reasons behind variations in kinetic energy despite constant frequency, touching on concepts from solid state physics and experimental methods.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why the kinetic energy of ejected photo-electrons varies even when the same frequency of light is used, suggesting a need for clarification on this phenomenon.
  • Another participant introduces methods to determine the work function of metals, referencing thermionic emission as a related technique.
  • A request for further explanation on the differing velocities of ejected electrons is made, indicating that provided resources do not adequately address this aspect.
  • A participant explains that the variation in kinetic energy is related to the nature of the material and the concept of the Fermi energy, noting that photons can excite electrons with a range of energies, leading to different kinetic energies for ejected electrons.
  • One participant expresses agreement with the explanation provided about the energy levels and the emission of electrons with varying energies.

Areas of Agreement / Disagreement

Participants express differing views on the explanation of kinetic energy variations, with some seeking clarification while others provide insights based on solid state physics. The discussion does not reach a consensus on the underlying reasons for the observed phenomena.

Contextual Notes

The discussion highlights the complexity of the photoelectric effect, including the dependence on material properties and the energy levels of electrons. There are unresolved aspects regarding the relationship between photon energy and the kinetic energy of ejected electrons.

Who May Find This Useful

This discussion may be of interest to those studying the photoelectric effect, solid state physics, or experimental techniques in physics.

Esfand Yar Ali
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It is explained in a book that to know the kinetic energy of the photo-electrons ,we reverse the polarity so that the minimum energy can be known.but I want to know that if we are incidenting same frequency of light on the metal surface and we also know that energy is directly proportional to freaquency then the kinetic energy of the ejecting photo-electrons should be same,but it was written in that book that kinetic energy of the ejecting electrons are diffrent.please explain this phenomenon
 
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There are several ways to find the work function of a metal:

Here is a nice description of the thermionic method:
http://avs.org/AVS/files/96/96788451-2031-48b4-a768-73b94102cd5e.pdf

When you analyze the lab technique used with photo emission, you will find some similarities with the thermionic method: http://demoweb.physics.ucla.edu/node/118
 
I need some explanations about this phenomenon of 'diffrent velocities' of the ejected electrons,the links you've given have no explanation on this
 
This has more to do with the nature of the material, and thus, requires an understanding of solid state physics.

Photoelectric effect are typically done on metals, which has a conduction band consisting of "free" electrons. This is an energy band (google it), the highest of it (in a relative term) are the electrons at the Fermi energy (at T=0K).

When a photon hits a metal, that photon has the probability of exciting electrons with a range of energies, not just the ones right at the Fermi energy. It can excite those below those electrons as well. If the electrons that are excited below the Fermi energy will acquire a different energy than the one excited from the Fermi energy, because these electrons are "deeper" in the energy "well". So they will end up with a different kinetic energy.

Since this band is continuous, you can expect, with bombardment of many photons, electrons being emitted with a range of energies.

Zz.
 
I think this explanation is good Zapper
 

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