Keywords for Work Function or E_photon?


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KC Navarro_1H
Posts: 33
Joined: Fri Apr 06, 2018 11:04 am

Keywords for Work Function or E_photon?

Postby KC Navarro_1H » Mon May 07, 2018 5:59 pm

What are some keywords to look out for if we need to find the Work Function or E_photon?

For example, there are questions from last Friday's review session like:

No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50 x 10^16 Hz. How much energy is required?

and

What is the wavelength that causes the ejected electron?

For the first question, you just use E = hv and for the second question, you use the whole E_photon - Φ = 1/2mv^2 to find E_photon. Should "required" be a keyword for the work function and "required" for the ejected electron? What are some other keywords to look out for?

Cindy Nguyen 1L
Posts: 48
Joined: Fri Apr 06, 2018 11:04 am

Re: Keywords for Work Function or E_photon?

Postby Cindy Nguyen 1L » Mon May 07, 2018 9:09 pm

I don't think you should necessarily memorize keywords in order to use different equations. Different problems have different contexts. In the example you gave for last Friday's midterm session, you had to use the work function + the kinetic energy to eventually find the wavelength because in the first part of the question, it told you that the ejected electron had kinetic energy. If it didn't tell you that the ejected electron had kinetic energy, you would just use the work function to find the energy of the photon and then the wavelength for it (because kinetic energy would be 0). That kind of question might be worded something like "What is the lowest wavelength for this electron to be ejected" or something.

TL;DR: If the entire problem doesn't specify extra energy, kinetic energy, etc., then you can just find the minimum energy required/lowest wavelength/frequency/etc. If it does, then you have to calculate that into your equations as well.

sharonvivianv
Posts: 63
Joined: Fri Apr 06, 2018 11:05 am

Re: Keywords for Work Function or E_photon?

Postby sharonvivianv » Sun May 13, 2018 12:11 am

You should know what the work function means exactly. It is the threshold energy. So when they ask for a minimum amount of energy of the photon to meet the threshold energy, there will be no kinetic energy. The threshold energy will not cause any electrons to bounce off. Any value greater than the threshold or the work function will produce kinetic energy.

Jacy Black 1C
Posts: 30
Joined: Fri Apr 06, 2018 11:01 am

Re: Keywords for Work Function or E_photon?

Postby Jacy Black 1C » Sun May 13, 2018 9:45 pm

Most times, if it asks for the energy required to eject an electron, this means it is asking for the work function, or the threshold energy. If it’s asking for the wavelength that caused the electron to be ejected, it is most likely asking for you to solve for the E Photon, and then find the wavelength of that photon.

Jose Hernandez 1D
Posts: 16
Joined: Tue Nov 14, 2017 3:02 am

Re: Keywords for Work Function or E_photon?

Postby Jose Hernandez 1D » Sun May 13, 2018 10:58 pm

One of the keywords you should be looking for is threshold energy, if this comes up in the problem being asked you know you will not be solving for the e photon. If you see wavelength then you know you will be solving for e photon.


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