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hey, can u guys help me? ive been trying to figure this one out forever. :(


1. Which of the following could NOT be used as a definition for resistance?

A. R = -( ∫ E dx) / I (that's the integral of Edx, over I, if your browser doesn't show it clearly)
B. R = -( ∫ E dx) / qI (that's the integral of Edx, over qI)
C. R = ΔU / qI
D. R = ΔV / I
 

aamartin81

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ARAP said:
It could be choice C.
I've taken 3 of the 4 old AAMC exams and have come across nothing like this, don't stress about it!

Adam
 

DHMO

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Yeah, you won't see any calculus on the MCAT. But even if you don't know any calculus, you can still use those test taking skills to narrow down the choices. Choices A and B are mutually exlusive (they added a variable into equation B), so the 'wrong' answer must be one of those. From this, you can infer that choices C and D are correct, so you are left with the question of whether -( ∫ E dx) = ΔV (in which case the 'wrong' answer would be B) or ΔU (in which case the wrong answer would be A). My feeling is that it is the latter because -( ∫ E dx) seems like potential energy, but I haven't taken any physics or calculus for 5 years.
 

Mediculous

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ARAP said:
It could be choice C.
Yeah, I agree, something like this won't be on the MCAT. Just for fun, though, I'll try it.
I don't think it would be choice C because(I don't have any fancy schmancy MAPLE-like font) the change in U=q(change in V)
change in V= I(R)
So, answers C and D are the same(at least in my mind) because once substituted with the equations above, choice C looks like: R=qV/qI=V/I

As a caveat, I've never had calc. based physics but I have had 2 semesters of calculus, so here's my go at it:
E=kq/(x^2)
the integral of that in respect to x=(-)kq/x=(-)V
and R=V/I, =>
after substitution, choice A is right, but choice B is incorrect because of (q) added to the denominator.

Frickin' Awesome!
 

Mediculous

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DHMO said:
Yeah, you won't see any calculus on the MCAT. But even if you don't know any calculus, you can still use those test taking skills to narrow down the choices. Choices A and B are mutually exlusive (they added a variable into equation B), so the 'wrong' answer must be one of those. From this, you can infer that choices C and D are correct, so you are left with the question of whether -( ∫ E dx) = ΔV (in which case the 'wrong' answer would be B) or ΔU (in which case the wrong answer would be A). My feeling is that it is the latter because -( ∫ E dx) seems like potential energy, but I haven't taken any physics or calculus for 5 years.
I would definitely agree with the test-taking strategy above. If you didn't have the luxury of time, a quick scan eliminates C and D because of the obvious difference in A and B when the equations are all supposed to equal each other. You know, I would be apprehensive towards anything DHMO says. After all, in large amounts, DHMO can be fatal. True story.
 

Shrike

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The best response so far is dhmo's, first pointing out that no such question would ever appear on the MCAT, then using process of elimination to raise the chances to 50%.

In case you want to know the answer to the very non-MCAT question asked:

Every MCAT-taker should know V=IR. Some will know, though it is not required, that V (voltage, or potential) arises as a function of E; specifically, it is the definite integral of E dx. From these two equations, we get R = V/I = (integral of E)/I. (Tracking negatives is irrelevant, here and usually -- you just use common sense at the end, and in this case common sense says we don't care because only one of them is in the answer choices.) So choice a works, and b is the answer to the original question.

But again: Not on the MCAT! Don't worry about this sort of thing!

Shrike
TPR lots o' stuff
 

anavistas

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Sinapse that's a very easy question. just playing with words!
First of all D is obviously correct as we know the V=IR law
secound U=Vq so C is also using V=IR law and it's correct
R = -( ∫ E dx) / It may not make any sense but if u multiply an q in that and divide it to q again -( ∫ E qdx) it's obviously -( ∫ Fdx) wich is U and is equal to Vq then Vq/qI is again the V=IR law and so A is correct .
but the answer B V=IRq and is incorrect!.Q.E.D
it's just a combination of mechanics and electronics!
well i'm a physics major! :p loodluck :luck:
 

NorCalGirl

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DHMO said:
Yeah, you won't see any calculus on the MCAT. But even if you don't know any calculus, you can still use those test taking skills to narrow down the choices. Choices A and B are mutually exlusive (they added a variable into equation B), so the 'wrong' answer must be one of those. From this, you can infer that choices C and D are correct, so you are left with the question of whether -( ∫ E dx) = ΔV (in which case the 'wrong' answer would be B) or ΔU (in which case the wrong answer would be A). My feeling is that it is the latter because -( ∫ E dx) seems like potential energy, but I haven't taken any physics or calculus for 5 years.
Wow, that's hot. :love: I think I'm in love.
 

Shrike

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Mediculous said:
Geez, Shrike, you didn't have to stick me on the barbed wire.
You're right; predation unintended and unecessary. You said what I said. I just wanted to emphasize the process, and which parts a test-taker should and might not know. But your answer shouldn't have been slighted; my bad.

As far as I've been able to tell, nobody else has any any idea what the barbed wire thing means. Thanks for knowing.
 

Mediculous

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Shrike said:
You're right; predation unintended and unecessary. You said what I said. I just wanted to emphasize the process, and which parts a test-taker should and might not know. But your answer shouldn't have been slighted; my bad.

As far as I've been able to tell, nobody else has any any idea what the barbed wire thing means. Thanks for knowing.
Ok, I'm all better now. I thought that, since there must be a lot of bio majors on SDN, more people would get the shrike's version of "bling". Or if they were at least from the South. Shrikes up, hoes down.