Work Function

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Alyssa Wilson 2A
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Joined: Fri Sep 28, 2018 12:18 am

Work Function

Postby Alyssa Wilson 2A » Wed Oct 17, 2018 8:30 pm

Hi, will the work function always be given to us in the problem when solving for the kinetic energy?

rosemarywang4i
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Re: Work Function

Postby rosemarywang4i » Wed Oct 17, 2018 8:31 pm

Constants will always be given on the front page for exams :)

Pipiena Malafu 4G
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Re: Work Function

Postby Pipiena Malafu 4G » Wed Oct 17, 2018 8:51 pm

It depends - this question is fairly vague. Read the information thoroughly and figure out based off of the problem and the given information.

Vanessa Reyes_1K
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Re: Work Function

Postby Vanessa Reyes_1K » Thu Oct 18, 2018 10:17 pm

For problem 1.69b do you have to convert electron volts to joules, and then use the E=hc/frequency equation?

Carissa Young 1K
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Re: Work Function

Postby Carissa Young 1K » Thu Oct 18, 2018 10:21 pm

Vanessa Reyes_4C wrote:For problem 1.69b do you have to convert electron volts to joules, and then use the E=hc/frequency equation?


Yes, you have to make sure all your SI units are correct before doing the problem.
1eV=1.602 x 10^-19 J

ThomascnguyenDis1J
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Re: Work Function

Postby ThomascnguyenDis1J » Sat Oct 20, 2018 12:57 am

I believe it is possible to find the work function if given only the frequency of the photon, using the equation:

E=hv, which will then equal the work function to eject the electron.

Alexandra Albers 1D
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Re: Work Function

Postby Alexandra Albers 1D » Sat Oct 20, 2018 3:55 pm

I think that the work function depends on the problem, the equation with the work function is Kinetic Energy = hv - work function, so if you have the other values you can compute it that way, but I think otherwise some number for the work equation needs to be given in the problem. If that is the case, should we memorize the number to convert electronvolts to joules?

Josephine Lu 4L
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Re: Work Function

Postby Josephine Lu 4L » Sat Oct 20, 2018 3:56 pm

Is the unit of work function Joules, or Joules per photon?

Brice McKeown 3D
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Re: Work Function

Postby Brice McKeown 3D » Sun Oct 21, 2018 4:53 pm

Could someone reiterate to me what Dr. Lavelle said about the 1/2mv^2 when the energy supplied by a photon (hv) is equal to the work function (phi).

Brice McKeown 3D
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Re: Work Function

Postby Brice McKeown 3D » Sun Oct 21, 2018 4:57 pm

Also, I am a little confused on what it means when the electron is ejected from the metal. Like is it light? Like what is the purpose of the electron being ejected?

cara_cavarretta_3F
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Re: Work Function

Postby cara_cavarretta_3F » Sun Oct 21, 2018 5:43 pm

In metals, free electrons may float about the metal but do not have enough energy to escape from the surface. When additional energy is added in the form of a photon that reaches the threshold energy, these free electrons can escape from the surface of the metal and be emitted

ariana_apopei1K
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Re: Work Function

Postby ariana_apopei1K » Sun Oct 21, 2018 5:44 pm

Brice McKeown 3D wrote:Also, I am a little confused on what it means when the electron is ejected from the metal. Like is it light? Like what is the purpose of the electron being ejected?

It has to do with the experiment we discussed in class where light (photons) hit a block of metal, leading to the e- being ejected. The main takeaway from the experiment was that light has particle properties, not only wave-like properties, meaning a larger wavelength will not mean more e- are ejected. The work function equation that people are discussing above can be used to calculate how much energy is needed from the photon to eject an electron from a specific metal.

SydBenedict2H
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Re: Work Function

Postby SydBenedict2H » Sun Oct 21, 2018 6:33 pm

If the energy of the light (photons) is higher than the work function (the little symbol that looks kind of like the green lantern symbol) then its met the "threshold" and can eject an electron. The difference between the work function (threshold) and the energy from the light equates to what the kinetic energy of the electron being ejected will be. It doesnt really happen but if the energy from the light is equal to the work function then the electron would be ejected but with a kinetic energy of 0.

Millicent Navarro 1I
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Re: Work Function

Postby Millicent Navarro 1I » Sun Oct 21, 2018 6:41 pm

Josephine Lu 1L wrote:Is the unit of work function Joules, or Joules per photon?


The unit for work function is Joules. Moreover--work function is a measure of energy, and energy is measured in the units of Joules.

Matthew Mar 1J
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Re: Work Function

Postby Matthew Mar 1J » Sun Oct 21, 2018 8:03 pm

In most of the problems I've seen, they don't usually give a number as the work function outright. Generally it's referred to as "the energy required to remove an electron from _____ surface" or whatever. I've also seen problems where the frequency or wavelength is given rather than the energy and you just use the equations to figure out the work function from there.

yuetao4k
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Re: Work Function

Postby yuetao4k » Sun Oct 21, 2018 10:58 pm

Josephine Lu 1L wrote:Is the unit of work function Joules, or Joules per photon?


The unit for work is joules! And joules = kg.m^2.s^-2

Angel Chen 2k
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Re: Work Function

Postby Angel Chen 2k » Sun Oct 21, 2018 11:16 pm

Work function is essentially the energy required to eject an electron. The equation of the work function is work function = h* Vo ( with Vo being the minimum frequency needed to eject an electron). Sometimes work function us given in eV so make sure to covert eV into Joules to avoid unit confusions.


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