Conductors and Gauss Law

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Homework Statement


http://img21.imageshack.us/img21/8079/orderyy3.th.jpg [Broken]


Homework Equations





The Attempt at a Solution



Well all I know that the smallest will be C, as it's 0 (inside the conductor), I think the next one is A, and I don't know about B and D
 
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Answers and Replies

  • #2
LowlyPion
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Inside the inner shell at A is 0, as for B and D which one is farther away from the charge source?
 
  • #3
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so A and C are both 0? D is farther... but flux isn't associated with radius isn't it
 
  • #4
Delphi51
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Imagining a Gaussian sphere enclosing the charge as far out as A, it would have less charge than a sphere at B.
The field at D will be smaller than B because it is spread out more in space.
Pretty tough to compare A and D.

I don't know how this works. What makes E = 0 in the conducting layer? It seems to me that the field due to the central charge would cause a charge separation in conducting layer C, so that (assuming central q is positive) there will be a layer of negative charge on the inner side of layer C and a positive one on the outer side. Do you know if that is correct?
 
  • #5
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E = 0 in the conducting layer because the electric field is 0 inside the conductor
 
  • #6
LowlyPion
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What makes E = 0 in the conducting layer?

If there were an E-field inside the conductor ... and the electrons are free to move ... how can an E-field be maintained?

Here's a lecture that covers this and more on electrostatics:
(about 20 min in. Though the whole lecture is good.)
 
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  • #7
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If there were an E-field inside the conductor ... and the electrons are free to move ... how can an E-field be maintained?

Here's a lecture that covers this and more on electrostatics:
(about 20 min in. Though the whole lecture is good.)

Therefore I was right that there is no E field inside the conductors right?
 
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  • #8
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Yes, there should be no E-field inside a conductor, therefore the charge enclosed by a Gaussian surface drawn inside a conductor should be zero.
 
  • #9
Nabeshin
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Inside the inner shell at A is 0, as for B and D which one is farther away from the charge source?

The inner shell isn't zero, because it's an insulating shell instead of conducting, so charge is distributed uniformly.
 
  • #10
LowlyPion
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The inner shell isn't zero, because it's an insulating shell instead of conducting, so charge is distributed uniformly.

If the point A is inside the shell - shell being the operative word - and inside of that then, it is 0. If it were a solid sphere with uniformly distributed charge, you would be correct (if A is not the center). But they call it a shell.
 
  • #11
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So what is the charge on A then?
 
  • #12
gabbagabbahey
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If the point A is inside the shell - shell being the operative word - and inside of that then, it is 0. If it were a solid sphere with uniformly distributed charge, you would be correct (if A is not the center). But they call it a shell.

Hmmm....this problem is certainly open to some interpretation!

If it is indeed a shell, and if A is inside the shell; even that doesn't guarantee the field is zero inside. Charge isn't free to distribute itself on an insulator, so there is no guarantee that the charge Q is uniform over the insulating shell. If it isn't uniform, then the field will not be zero.

I suspect that you are to assume that the charge Q is not distributed uniformly over the shell, and that the point A is very close to the charge, producing a large field at A. But that's just a guess.

@EquinoX--- You should probably ask for clarification from your prof or a TA.
 

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