AAMC Chem/Phy Section Bank 12

[bellowbruins]

Hi all, I am confused with the question when the question said "NOT" and they minus -3.4 eV from total Energy. Can someone help me with this question as to why they minus -3.4 eV ? I got 20.5 eV and go with B. AND what does that NOT in the question even mean lol. I am confused with the wording also.

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[deleted853480]

What's the question?

 

[bellowbruins]

@aldol16 hello can you help me out with this question please! Thanks

 

[aldol16]

Yeah, what's the question? I no longer have access to AAMC materials.

 

[drms2015]

Yeah, what's the question? I no longer have access to AAMC materials.

I was also confused by this.
The question is: "What is the kinetic energy of a photoelecron produced in the energy meter of the photoacoustic calorimetry device when the frequency of an incident photon that is NOT absorbed in the solution is f=5.0x10^15 Hz? (Note: Use h=4.1x10^-15 eV*s)." The passage includes, "The energy meter, based on the photoelectric effect, uses a detector with a work function of 3.4 eV."

 

[Akela98]

Off the top of my head, the equation to be used is KEmax = hf-(work function). So h(4.1 times 10^-15) times f(5.0 times 10^15) would equal 20.5 eV. The work function is simply 3.4.

Therefore the answer is 20.5-3.4= 17.1 eV.

The reason they used NOT is because you have to understand what is going on in the problem. The photon energy that is ABSORBED by the solution goes into creating a sound wave which is received by the microphone. As such when they say "the energy meter, based on the photoelectric effect" they are telling you that the sample is losing photons via the photoelectric effect and these are not absorbed by the solution. In the photoelectric effect, energy is used to knock off photons. They are registered by the energy meter and its particular equation must be known.

The reason you most likely missed this problem is because you may have skimmed the paragraph rather than understanding the setup of the experiment.

 

[aldol16]

So work functions are something we don't usually teach but are important in solid-state chemistry. Think of a work function as an overhead cost. You always have to pay it in order to get the electron moving. It's the minimum energy you need to move an electron at all. So say you shoot 20 eV of energy at an electron. By energy conservation, it's excited 20 eV. 3 eV is paid into the overhead cost, leaving it 17 eV to convert to kinetic energy.

 

[silverlinings0618]

SDN Week 16 post 3

1. “Does free will exist?” Khan: free will=better as emergent property than explained by quantum mechanics

2. “Alcoholism” JW: best treatment= appeals to their values and goals

3. “Galatians” JW: difference b/t Jews and Christ = how they read old testament

4. “Stockhausen” JW: Stockhausen revolutionizes by combining both machine and man

5. “Puritan society” Khan: rose= the Scarlet letter= enlightens the sorrow of the prison= the woman