E=hv vs. Work Function?


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Rachel Min
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Joined: Fri Sep 29, 2017 7:04 am

E=hv vs. Work Function?

Postby Rachel Min » Thu Nov 09, 2017 5:05 pm

Is the best indicator of when to use E=hv vs. E=Ek+work function just whether or not the question asks about a photon or electron? I know sometimes we need to find the energy of photons for the work function equation, but is that for the threshold energy or just the normal energy? I don't think my question makes much sense...

Lena Nguyen 2H
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Re: E=hv vs. Work Function?

Postby Lena Nguyen 2H » Thu Nov 09, 2017 5:24 pm

The equation is kinetic energy = photon energy + work function. If you're finding the energy of the photon given frequency or wavelength, you would use E = hv. For electrons given velocity or kinetic energy, you would use DeBroglie's equation. The work function is the threshold energy, which you would be able to find only if you were able to figure out the photon energy and kinetic energy of the electron.

Mika Sonnleitner 1A
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Re: E=hv vs. Work Function?

Postby Mika Sonnleitner 1A » Thu Nov 09, 2017 9:43 pm

You would use the equation E=hv when asked to find the energy of the photon. However, if you were asked to find anything related to the emitted electron, you would use the overall photoelectric effect equation, E(photon) - work function = Ek. For example, if you were asked to find the velocity of the electron, you would have to plug in values for the energy for the photon and the work function, solve for kinetic energy, then use Ek = (1/2)mv^2 to solve for the velocity.

However, if you were asked to find the wavelength of the ejected electron, you would use DeBroglie's wavelength equation, because an electron is a particle that has mass. If you were asked to find the wavelength of the incoming light, you would use E=hv and c=λv (λ=hc/v), since light is a particle that has no mass. In summary, you use DeBroglie's wavelength equation for particles with mass (like electrons or protons), and you would use E=hv for particles with no mass (such as light).


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