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msamadia
Joined: 02 Aug 2006
Posts: 13
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 Posted: Sun Aug 09, 2009 5:19 pm Post subject: |
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I got this question wrong b/c i was thinking that Pouiseille's law with resistance and the radius to the fourth power?
How will i know on the MCAT when i can use this and the resistance..
is this the AV=constance flow eqn? |
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mcat_premed3832
Joined: 19 Oct 2006
Posts: 412
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| Posted: Tue Aug 11, 2009 7:24 pm Post subject: Resistance and radius |
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Using Pouiseille's law on the MCAT, in the absence of them providing the equation to you, is very rare. Not to mention, Pouiseille's law and the AV (flow) equation are used for fluid dynamics which is not focus of the question stem.
Wires and resistance should have you consider electricity and relationships between resistance and radius. (PHY 10.2, 3.3 in the GS text or http://hyperphysics.phy-astr.gsu.edu/hbase/electric/resis.html ). |
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quadalpha
Joined: 21 Feb 2010
Posts: 65
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| Posted: Tue Mar 09, 2010 10:20 pm Post subject: |
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| Perhaps the question can mention that the lengths of the wires are equal? Right now, it might sustain a reading wherein the wires are drawn from same "blocks" of material, which would mean one has four times the cross sectional area and one quarter the length, giving 16:1. |
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mcat_premed3832
Joined: 19 Oct 2006
Posts: 412
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| Posted: Mon Mar 22, 2010 4:32 am Post subject: |
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Being of the same lengths is a reasonable thing to specify in a question; however, given the nature of a wire, I don't understand your interpretation of "drawn from the same material"?
Just to clarify:
Typical definition: A wire is a single, usually cylindrical, elongated strand of drawn metal.
Wikipedia definition: A wire is a single, usually cylindrical, string of metal . . . commonly formed by drawing the metal through a hole in a die or draw plate.
http://en.wikipedia.org/wiki/Wire |
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quadalpha
Joined: 21 Feb 2010
Posts: 65
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| Posted: Mon Mar 22, 2010 9:25 pm Post subject: |
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| mcat_premed3832 wrote: | | Being of the same lengths is a reasonable thing to specify in a question; however, given the nature of a wire, I don't understand your interpretation of "drawn from the same material"? |
Wires are typically drawn (pulled) from a block of material. Does that make things clearer? |
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mcat_premed3832
Joined: 19 Oct 2006
Posts: 412
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| Posted: Mon Mar 22, 2010 9:34 pm Post subject: |
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| Now you are asking a super tough question! When defining "wire" in physics, it's rare to see a definition without the word "drawn"; so you are right that "pulled" would be more clear but you would have gotten "pulled" correct on the real MCAT but not "drawn" (which is more common). If we had both in the question, you might not have remembered "drawn" 2 months from now. We want to get you ready for the real thing and I don't think you could possibly get this question type wrong in the future. |
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quadalpha
Joined: 21 Feb 2010
Posts: 65
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| Posted: Mon Mar 22, 2010 9:52 pm Post subject: |
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| mcat_premed3832 wrote: | | Now you are asking a super tough question! When defining "wire" in physics, it's rare to see a definition without the word "drawn"; so you are right that "pulled" would be more clear but you would have gotten "pulled" correct on the real MCAT but not "drawn" (which is more common). If we had both in the question, you might not have remembered "drawn" 2 months from now. We want to get you ready for the real thing and I don't think you could possibly get this question type wrong in the future. |
Okay, cheers  I was thinking too hard. |
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