Kaplan Is Conceptually Wrong!!!

[mterp45]

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I ran into a problem while using Kaplan's Qbank. The question was on the photoelectric effect and it's really borthering me. Kaplan seems to be treating Binding energy, and work function as if they are the same thing. This is entirely false, I have always known that the binding energy is the energy needed to augment the electron to the fermi level, and that the work function is the treshhold energy corresponding to energy needed to augment the electron's from the fermi to the vacuum level.

According to Kaplan:

Energy of a photon= binding energy of electron + kinetic energy of electron

This has to be wrong!!!, the binding energy simply cannot be treated as the work function Right?

Well I guess the real question is:

Does AAMC treat work function and binding energy as anologues? and for MCAT purposes, should I just treat the two as if they were the same? what do you think? have you discussed this before?

 

[Mandek]

whats Qbank? is it a review book? never heard of it...

 

[RSAgator]

should i be worried that i have no clue what you're talking about? 😀

what topic does this concern?

 

[hum3a]

i believe the equation is: photon energy (hf) = maximum kinetic energy of ejected electron (in joules) + the work function (minimum energy need to eject the electron in joules)

You could treat the binding energy as the work function i suppose but i have never heard of this. But the energy needed to eject the electron should be the energy needed to break the bond between the electron and the atom. right?

 

[RapplixGmed]

Kaplan's Qbank is kind of bad. I've noticed several errors with it. It is also relatively inconsistent in difficulty level. I don't recommend studying with it unless you're looking for some extra practice material AND its a few weeks before the exam so u can burn through the Qbank and then get your bearings back on real practice exams.

 

[Vihsadas]

Don't worry about the fermi level and vacuum level. The binding energy of an electron is the energy needed to release it from its atomic (molecular) orbit for MCAT purposes. In the derived photoelectric equation:

Hv = phi + KE

phi is the energy required to remove the electron from the atom, and is considered by the MCAT to be the work function. (It's been a long while...I'm pretty sure that I'm right though.)

EDIT: And yes, there are a number of errors in Kaplan's Qbank, but I don't think this is one of them.

 

[Mandek]

whats Qbank??

 

[mterp45]

i believe the equation is: photon energy (hf) = maximum kinetic energy of ejected electron (in joules) + the work function (minimum energy need to eject the electron in joules)

You could treat the binding energy as the work function i suppose but i have never heard of this. But the energy needed to eject the electron should be the energy needed to break the bond between the electron and the atom. right?

ok

 

[mterp45]

should i be worried that i have no clue what you're talking about? 😀

what topic does this concern?

It concerns the photoelectric effect, and NO you shouldn't be worried about it. It's just the physics major part of me that worries about such things, just know that hf= electron emission energy + K.E and you will be ok.

 

[Vihsadas]

Well I am a physics major, and I had never heard of treating the binding energy as the work function either until I came across that question. I think doing so is completely incorrect, but I am willing to do so for the MCAT, as long as can be reassured that aamc treats them analogously.

I'm a physics major too so I know what you mean. On the MCAT, the types of questions that you'll get will give you something like:

The work function of an electron is XeV, if YeV worth of energy is put into the electron to eject it, what will its kinetic energy be?

In terms of terminology, I don't remember if the MCAT explicitly confuses Binding energy and work function but I wouldn't worry about it too much.

 

[mterp45]

I'm a physics major too so I know what you mean. On the MCAT, the types of questions that you'll get will give you something like:

The work function of an electron is XeV, if YeV worth of energy is put into the electron to eject it, what will its kinetic energy be?

In terms of terminology, I don't remember if the MCAT explicitly confuses Binding energy and work function but I wouldn't worry about it too much.

lol Thanks.

 

[mterp45]

Kaplan's Qbank is kind of bad. I've noticed several errors with it. It is also relatively inconsistent in difficulty level. I don't recommend studying with it unless you're looking for some extra practice material AND its a few weeks before the exam so u can burn through the Qbank and then get your bearings back on real practice exams.

Actually, don't get misconstrued by my post. Kaplan's Qbank is an extremely useful and challenging tool. It is great way to increase your score without wasting any of the full lentghs. I have noticed that many on this site wonder if and when they should start taking full lentghs, whether it's better to wait until their done reviewing. Well, the Qbank allows you to effectively combine the review process with timed, full lentgh stimulated practice. I highly recommend it.

 

[Vihsadas]

That's a good point, and it probably did contribute to my success somewhat. It allowed me to do some questions during my review period. The questions are very difficult. And, there tend to be a few errors. It was s decent review tool in my opinion.

 

[Mandek]

What is Kaplan Qbank? Does it come with the course?

 

[majik1213]

I ran into a problem while using Kaplan's Qbank. The question was on the photoelectric effect and it's really borthering me. Kaplan seems to be treating Binding energy, and work function as if they are the same thing. This is entirely false, I have always known that the binding energy is the energy needed to augment the electron to the fermi level, and that the work function is the treshhold energy corresponding to energy needed to augment the electron's from the fermi to the vacuum level.

According to Kaplan:

Energy of a photon= binding energy of electron + kinetic energy of electron

This has to be wrong!!!, the binding energy simply cannot be treated as the work function Right?

Well I guess the real question is:

Does AAMC treat work function and binding energy as anologues? and for MCAT purposes, should I just treat the two as if they were the same? what do you think? have you discussed this before?

hey what's up .. i'm a physics major who took Modern Physics I where we dealth with that .. so hopefully I may be able to shed some light

in honesty, though, i'm no expert I guess on anything, but hear me out:

when an electron travelling freely through space collides into an atom lacking an electron in its ground state, the electron may get absorbed. If so, then a photon can be released in this process. The photon will then have energy equal to the initial kinetic energy of the electron before hitting the atom plus the energy the electron gained from the atom in becoming bound (at the expense of the atom's "effort," if I may, to bind the electron).

as for your "real" question, rely on your knowledge from a level of physics no higher than modern physics I .. in modern physics II, we spent a lot of time solving the TDSE and TISE .. and we discussed fermions briefly.


now I have a question: can photons be released when electrons are ejected form an atom? Or only when they fall back into a ground state? the photon java applet here seems to suggest only the former is possible.

 

[Vanguard23]

Keep ignoring Mandek. He MUSTN'T know the truth!