Photoelectric effect and maximum kinetic energy

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Discussion Overview

The discussion revolves around the calculation of the work function of a metal (specifically Sodium) in the context of the photoelectric effect. Participants explore the relationship between maximum kinetic energy of emitted electrons, photon energy, and the work function, while addressing assumptions and methods for measurement.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant proposes using the equation KE = hf - W to find the work function, questioning whether to assume the velocity of the electron or photon is the speed of light.
  • Another participant suggests that there is no need to assume a velocity, as the kinetic energy and photon energy can be used directly to calculate the work function.
  • A later reply clarifies that the participant initially misunderstood the availability of kinetic energy, indicating uncertainty about whether to consider photons or electrons in the calculations.
  • One participant emphasizes that in standard experiments, maximum kinetic energy is typically measured directly through stopping potential, which provides necessary information to find the work function.
  • Another participant asks how to calculate the work function if the stopping potential is known.
  • A participant shares a link to a typical photoelectric effect experiment description, indicating it may not be appropriate for school-type work.
  • The original poster expresses gratitude for the provided link and clarifies that the inquiry is for personal interest, not academic work.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of assumptions regarding velocity and the method of measuring maximum kinetic energy. There is no consensus on the best approach to calculate the work function, as multiple perspectives on the experimental setup and calculations are presented.

Contextual Notes

Participants mention the relationship between stopping potential and maximum kinetic energy, but there are unresolved details regarding the specific experimental setup and the definitions of variables involved in the calculations.

doc.madani
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Hey guys, assume that i performed and experiment to measure the maximum kinetic energy of electrons released due to the photoelectric effect due to light falling on a metal target (i.e. Sodium).

KE = hf - W (where W = work function, f = frequency and h = Planck constant)

since KE = 1/2 mv^2

i need to find the work function of this metal due to the photoelectric effect, do i assume the the velocity of the electron (or photon confused :S) is traveling at 3x10^8 (c) ??

p.s. i have all other known variables excluding W

thanks.
 
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Er.. why do you even need to make any assumption about the velocity? You have KE, and presumably, you can determine the photon energy. What's left is simply plug and chug into the photoelectric effect equation to get the work function!

Or am I missing something here?

{scratching head}

Zz.
 
Oh very sorry i was not given the kinetic energy, however i knew the mass of the particle.
can't remember whether it was a photon or electron. In terms of calculating the work function for this particular experiment, is it the absorbed photons we need to consider in determining the work function?

very sorry for this silly question
 
So what exactly is this "experiment"?

You said that the experiment is to measure the max. KE. In most experiment, this is measured "directly", i.e. independent of the values of the work function, etc. In a standard photoelectric effect experiment, the max. KE is related to the stopping potential. So you get the value of the max. KE directly. This gives you ALL you need to find the work function of the metal.

Zz.
 
ZapperZ said:
So what exactly is this "experiment"?

You said that the experiment is to measure the max. KE. In most experiment, this is measured "directly", i.e. independent of the values of the work function, etc. In a standard photoelectric effect experiment, the max. KE is related to the stopping potential. So you get the value of the max. KE directly. This gives you ALL you need to find the work function of the metal.

Zz.

so then just say the stopping potential was 1.6 volts, how would you go on calculating W.
 
This is a description of a typical Photoelectric effect experiment in an undergraduate physics lab. Read it.

http://mypages.iit.edu/~segre/phys223/08F/lab10_223.pdf

BTW, this better not be part of a school-type work, because you should know better by now where such a question should go into.

Zz.
 
thank you very much for that link explained a lot, and no its not school-type work, its simply personal leisure.
 

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