Work Function vs De Broglie

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Rachel Lipman
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Work Function vs De Broglie

Postby Rachel Lipman » Sat Nov 07, 2015 4:28 pm

Looking back at my notes from chapter one, I am confused about when to use just E=hv and when to actually use Ephoton = Ek + work function. Can someone please clarify, especially with the midterm question.

Umair Khan 2G
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Re: Work Function vs De Broglie

Postby Umair Khan 2G » Sat Nov 07, 2015 5:20 pm

The energy of a photon is is Planks constant (h) times the frequency (v), which is equal to E=hv. Work function is just the minimum amount of energy required to remove an electron, also known as threshold energy.
In other words, the formula you mention is exactly the same thing as hv=Ek + work function.
De Broglie's equation, on the other hand, is the relationship between wavelength and objects that have a mass and velocity.
In the photoelectric equation , v is the velocity is the speed of the electron.
De Broglie's Equation is , where h is Plank's constant, m is the mass of the electron, and v is the velocity of the electron.
By utilizing the velocity found for the kinetic energy of the electron, we can calculate its wavelength with De Broglie's equation. Aside from this work function and De Broglie are not used together very often.
Note that , which is equal to can not be used to find the wavelength of an electron, because it specific to the speed of light, i.e. photons.

Jake Ney lecture 1 discussion 1F
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Re: Work Function vs De Broglie

Postby Jake Ney lecture 1 discussion 1F » Sat Nov 07, 2015 5:20 pm

First, finding the de broglie wavelength of an object or particle involves calculating its momentum and h/p. This has nothing to do with the photoelectric effect. Second you often have to use E=hv in a problem involving the photoelectric effect to calculate the work function of a metal surface or to calculate the energy of incident light, given its frequency.

For example for question for on the fall 2012 midterm we are given the work function of chromium metal in eV. After converting this to Joules we use E=hv to calculate the frequency required to remove electrons from its surface. We can then calculate the wavelength required to remove electrons from the chromium surface using wavelength=c(speed of light)/v. This wavelength however is not the same as a de broglie wavelength.

Given the work function energy you could then also use the equation (Ephoton = Ek + work function) to relate energy of the incident light to the energy of the emitted photon.

JasmineAlberto4J
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Joined: Fri Sep 25, 2015 3:00 am

Re: Work Function vs De Broglie

Postby JasmineAlberto4J » Sat Nov 07, 2015 6:15 pm

the De Broglie equation is used when you are trying to find the wavelength of something with rest mass (i.e. an electron). A photon does not have rest mass so you use the equations E=Φ+ 1/2 mv^2 and λ=hc/E

Vanessa A 3F
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Joined: Fri Sep 25, 2015 3:00 am

Re: Work Function vs De Broglie

Postby Vanessa A 3F » Sat Nov 07, 2015 8:16 pm

E=hv simply means Energy = Planck's consant x velocity

Ephoton = work function + kinetic energy
is the same thing as
Eincident = Ethreshold + Eexcess
This is basically saying that in the photoelectric effect, the energy of the incident light that hits the metal (E photon), equals the minimum energy it takes to remove an electron from the metal's surface (Ethreshold/work function), plus whatever energy is left over (Eexcess/Kinetic energy).

Usually you would use E=hv to find either the energy, in Joules, of a light, or its frequency.

Ephoton = work function + kinetic energy
Is usually used to find out either how much kinetic energy an electron that is ejected has, how much energy the incident photon had, or what the work function of the metal was.
I hope this helps.


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