What exactly is Φ?


Moderators: Chem_Mod, Chem_Admin

Nane Onanyan 1G
Posts: 105
Joined: Wed Sep 30, 2020 9:43 pm
Been upvoted: 1 time

What exactly is Φ?

Postby Nane Onanyan 1G » Mon Oct 12, 2020 10:54 am

I understand that this is used in the work function, but how is it calculated? Is it just h(v)?

Alexa Pham 1D
Posts: 69
Joined: Wed Sep 30, 2020 10:03 pm

Re: What exactly is Φ?

Postby Alexa Pham 1D » Mon Oct 12, 2020 10:56 am

I think it's usually a value that's given in an equation. Or you could solve for it if they give you the energy of the photon. If that's the case, then you'd have to make the kinetic energy portion equal to 0 in order to find the minimum amount of energy (aka work function) needed to emit an electron from that metal.

KatarinaReid_3H
Posts: 184
Joined: Wed Sep 30, 2020 9:41 pm
Been upvoted: 4 times

Re: What exactly is Φ?

Postby KatarinaReid_3H » Mon Oct 12, 2020 10:57 am

Yes, the work function is the energy. In problems, it will usually give this value in Joules or eV(electron volt). 1eV is equal to 1.6 x 10^-19 Joules.

Andrew Wang 1C
Posts: 92
Joined: Wed Sep 30, 2020 10:11 pm
Been upvoted: 5 times

Re: What exactly is Φ?

Postby Andrew Wang 1C » Mon Oct 12, 2020 10:59 am

Φ is the amount of energy (unique to each element) that a photon needs to have for an electron to be ejected from a metal when it is hit with the proton. E = hv is the energy of a photon when it hits the metal (hv = Φ + Ek). So Φ would be equal to hv only if the electron is ejected with no excess energy.

I think Φ will be given to us in problems. Or we could also be solving for Φ, if the problem gives us enough info (hv and Ek).

Hope this helps!

Nika Gladkov 1A
Posts: 122
Joined: Wed Sep 30, 2020 9:33 pm
Been upvoted: 6 times

Re: What exactly is Φ?

Postby Nika Gladkov 1A » Mon Oct 12, 2020 11:01 am

is defined as the amount of energy required to remove an electron from a metal surface in a vacuum with the electron having 0 KE. You would calculate it by using the equation E(photon)- = E(excess) (or the kinetic energy). If you know the frequency of incoming light, you can use to calculate it's energy. Then, if you are given the velocity of the outgoing electron, you can use it to calculate the kinetic energy through the equation . Then, you would subtract the E of the incoming photon from the KE of the outgoing electron to get the work function. If the velocity of the outgoing electron is zero, the energy of the incoming photon is equal to the work function.

Shrey Pawar 2A
Posts: 96
Joined: Wed Sep 30, 2020 9:42 pm
Been upvoted: 3 times

Re: What exactly is Φ?

Postby Shrey Pawar 2A » Mon Oct 12, 2020 11:01 am

The Φ symbol is just meant to represent the work function which shows the threshold energy needed to excite the electron. Most of the time it is provided in the context of the problem, or you could use the equation that Alexa provided to find it, given you have the rest of the variables already. H(v) is just the energy of the photon so that is not the same thing. The h(v) in the equation is just there to show the intial amount of energy. When it is subtracted by the work function, we get the excess energy remaining, which is the kinetic energy of the electron excited. Hope this helps sorry it's a bit wordy!

Malakai Espinosa 3E
Posts: 91
Joined: Wed Sep 30, 2020 9:50 pm
Been upvoted: 1 time

Re: What exactly is Φ?

Postby Malakai Espinosa 3E » Mon Oct 12, 2020 11:21 am

Φ is described as the work function/threshold energy, but I don't believe there is an equation that we need to know in order to get the value on our own. This number is more determined through experimental data, and therefore beyond the scope of this class. If the work function is needed then the problem will give it to you, unless of course the problem is asking you to solve this variable.

Hope this helps!

Tessa House 3A
Posts: 91
Joined: Wed Sep 30, 2020 9:52 pm
Been upvoted: 1 time

Re: What exactly is Φ?

Postby Tessa House 3A » Mon Oct 12, 2020 11:35 am

This is the work function, which tells you the energy required to remove one electron from the metal. It can be given in problems in J or kJ, but in the case it is given in kJ/mol for a metal, you might need to calculate the energy required to remove one electron rather than one mole to solve other parts of the problem. You can also use the energy of the incoming light and kinetic energy to calculate it.

Nicoli Peiris 1B
Posts: 105
Joined: Wed Sep 30, 2020 10:02 pm

Re: What exactly is Φ?

Postby Nicoli Peiris 1B » Mon Oct 12, 2020 12:29 pm

This is the work function. To solve for this you would have to given some way to solve for or directly given the kinetic energy of the electron and the energy of the photon. Otherwise you would be given the work function value and would be asked to solve for something related to the kinetic energy or the energy of the photon.

Margaret Wang 2D
Posts: 90
Joined: Wed Sep 30, 2020 9:58 pm

Re: What exactly is Φ?

Postby Margaret Wang 2D » Mon Oct 12, 2020 12:35 pm

The work function is also known as the threshold energy, the energy needed to eject an electron. From what I understand, we will always be given the value. If we need to solve for it, it'll be with the equation E(photon) - (work function) = E(excess) and never any other way.

Aydin Karatas 1F
Posts: 119
Joined: Wed Sep 30, 2020 9:37 pm

Re: What exactly is Φ?

Postby Aydin Karatas 1F » Mon Oct 12, 2020 12:38 pm

It is the work energy. When looking at work energy in a problem, it's usually measured in Joules (J) of electronvolts (eV). Keep in mind that the work energy plus the excess energy (kinetic energy of an electron) is equal to the incoming energy of the photon.

Hope this helps!

Tiao Tan 3C
Posts: 100
Joined: Wed Sep 30, 2020 9:59 pm

Re: What exactly is Φ?

Postby Tiao Tan 3C » Tue Oct 13, 2020 1:50 am

It is the work function/threshold energy: the energy to remove electrons. It is usually given in the question so you don't have to worry! If not, then you would have to find it using the equation hv=Ek + Φ. I am sure the other conditions will be given for you to apply this equation.

Ximeng Guo 2K
Posts: 101
Joined: Wed Sep 30, 2020 9:54 pm

Re: What exactly is Φ?

Postby Ximeng Guo 2K » Tue Oct 13, 2020 2:01 pm

Energy required to remove an electron from the metal surface.

Total Energy provided by photons = energy required to remove 1 e- + kinetic energy of that removed e-

Simer_Shera_2D
Posts: 104
Joined: Wed Sep 30, 2020 9:58 pm
Been upvoted: 1 time

Re: What exactly is Φ?

Postby Simer_Shera_2D » Tue Oct 13, 2020 2:03 pm

The work function is the energy required to remove a single electron from a specific surface. From my understanding and the practice problems that I've done, it's always provided in the problem and does not need to be solved for.

Lorraine Jiang 2C
Posts: 102
Joined: Wed Sep 30, 2020 9:54 pm
Been upvoted: 1 time

Re: What exactly is Φ?

Postby Lorraine Jiang 2C » Wed Oct 14, 2020 6:14 am

The work function, which is also called the threshold energy, is the minimum amount of energy required for the e- on an atom to be removed!

Hope it helps!

Jiapeng Han 1C
Posts: 91
Joined: Wed Sep 30, 2020 9:50 pm

Re: What exactly is Φ?

Postby Jiapeng Han 1C » Wed Oct 14, 2020 8:24 am

Work function is the threshold energy--the minimum amount of energy needed to release electrons from a metal surface. Too calculate it, you need to know exactly at which frequency of light does the electrons get released. Then simply use the equation: E=h*f. If the energy of light is big enough to release electrons from metal surface, then to calculate the work function, you need to use the energy of the light to subtract the kinetic energy of the released electrons.

Shrinidhy Srinivas 3L
Posts: 108
Joined: Wed Sep 30, 2020 9:39 pm
Been upvoted: 2 times

Re: What exactly is Φ?

Postby Shrinidhy Srinivas 3L » Wed Oct 14, 2020 9:51 am

I think the most important thing that you need to remember about the work function is that it represents the threshold energy. The amount of energy that the photon comes in with minus the threshold energy gives you the kinetic energy of the ejected electron. Hope this helps!


Return to “Properties of Light”

Who is online

Users browsing this forum: No registered users and 1 guest