## Work Function

Alyssa Wilson 2A
Posts: 65
Joined: Fri Sep 28, 2018 12:18 am

### Work Function

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

rosemarywang4i
Posts: 34
Joined: Fri Sep 28, 2018 12:28 am

### Re: Work Function

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

Pipiena Malafu 3J
Posts: 39
Joined: Fri Sep 28, 2018 12:27 am

### Re: Work Function

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
Posts: 60
Joined: Fri Sep 28, 2018 12:28 am

### Re: Work Function

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

Carissa Young 1K
Posts: 65
Joined: Fri Sep 28, 2018 12:17 am

### Re: Work Function

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
Posts: 30
Joined: Fri Sep 28, 2018 12:16 am

### Re: Work Function

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
Posts: 61
Joined: Fri Sep 28, 2018 12:18 am

### Re: Work Function

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
Posts: 62
Joined: Fri Sep 28, 2018 12:18 am

### Re: Work Function

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

Brice McKeown 3D
Posts: 35
Joined: Fri Sep 28, 2018 12:25 am

### Re: Work Function

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
Posts: 35
Joined: Fri Sep 28, 2018 12:25 am

### Re: Work Function

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
Posts: 32
Joined: Fri Sep 28, 2018 12:23 am

### Re: Work Function

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
Posts: 89
Joined: Fri Sep 28, 2018 12:27 am
Been upvoted: 1 time

### Re: Work Function

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
Posts: 60
Joined: Wed Nov 08, 2017 3:00 am

### Re: Work Function

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
Posts: 61
Joined: Fri Sep 28, 2018 12:25 am

### Re: Work Function

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
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am
Been upvoted: 1 time

### Re: Work Function

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
Posts: 60
Joined: Fri Sep 28, 2018 12:27 am
Been upvoted: 1 time

### Re: Work Function

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
Posts: 59
Joined: Fri Sep 28, 2018 12:20 am

### Re: Work Function

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.