E field of a conductor with an arbitrary shape enclosing charge

In summary, the electric field outside an arbitrary shaped conductor won't be radially symmetric, resulting in a non-uniform charge density on the interior of a hollow sphere. If you want to find the field produced by a point charge at the origin, you have to use Gauss's theorem on a gaussian sphere around the charge. However, this calculation conflicts with the fact that the field is not symmetric because the arbitrary conductor has a non-uniform charge density on its surface.
  • #1
weezy
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Screen Shot 2017-06-16 at 3.32.22 PM.png

In this image charge q is enclosed within an arbitrary shaped conductor. I'm asked to find what if the Electric field in regions 1,2,3,4 are uniform and if the surface charge densities on the interior wall of the arbitrary shaped conductor and the hollow sphere conductor are uniform.

My analysis tells me that since the inner conductor is arbitrary the E field outside it won't be radially symmetric and thus should induce a non-uniform charge density on the interior of the hollow sphere. On the other hand since we know E field can't exist inside the hollow conductor, by Gauss's law we must have a uniform field in region 4.

What I am having trouble with is the following fact:

If I am to take a gaussian sphere of radius R in region 2 (it encloses the arbitrary shape) and apply Gauss's theorem, I should find the integral give me ## E = \frac{q}{4 \pi \epsilon R^2} ## which is just the E field produced by point charge located at the origin. However this conflicts the fact that the E field is not symmetric because I expect the arbitrary conductor to have uniform charge density on it's surface but due to it's arbitrary shape it'll have a non-uniform E field in region 2. What is happening here?

EDIT #1: Also I'd like to know if changing the position of q changes the E field in region 2. I think it does not if the arbitrary conductor has some thickness. I'm not entirely sure about this.
 
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  • #2
Is the conductor between 1 and 2? If yes, what is 3, another conductor?
weezy said:
My analysis tells me that since the inner conductor is arbitrary the E field outside it won't be radially symmetric and thus should induce a non-uniform charge density on the interior of the hollow sphere.
Right.
weezy said:
On the other hand since we know E field can't exist inside the hollow conductor
That is not true in general, assuming "inside" means vacuum inside the hollow conductor.
weezy said:
by Gauss's law we must have a uniform field in region 4.
That is not inside.

weezy said:
If I am to take a gaussian sphere of radius R in region 2 (it encloses the arbitrary shape) and apply Gauss's theorem, I should find the integral give me ## E = \frac{q}{4 \pi \epsilon R^2} ##
Only if you assume that the electric field has the same magnitude everywhere, otherwise you don't get this result.
Make a wrong assumption and you get a wrong result.
EDIT #1: Also I'd like to know if changing the position of q changes the E field in region 2. I think it does not if the arbitrary conductor has some thickness. I'm not entirely sure about this.
What do you know about the potential of the conductor at its surface? How does that change if you move the charge?
 
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  • #3
mfb said:
Is the conductor between 1 and 2? If yes, what is 3, another conductor?Right.That is not true in general, assuming "inside" means vacuum inside the hollow conductor.That is not inside.

3 is a hollow conductor sphere

mfb said:
Only if you assume that the electric field has the same magnitude everywhere, otherwise you don't get this result.
Make a wrong assumption and you get a wrong result.
Oh my! this is what I overlooked!

mfb said:
What do you know about the potential of the conductor at its surface? How does that change if you move the charge?

The surface must be equipotential so that means in any case the field shouldn't vary. Yet the answer key had my answer marked wrong.
 

1. What is the concept of "E field of a conductor with an arbitrary shape enclosing charge"?

The concept of "E field of a conductor with an arbitrary shape enclosing charge" refers to the electric field that exists around a conductor with a non-uniform shape that contains a charge. This charge can be either positive or negative and creates an electric field that extends into the surrounding space.

2. How is the electric field calculated for a conductor with an arbitrary shape enclosing charge?

The electric field is calculated using Gauss's law, which states that the electric flux through any closed surface is equal to the charge enclosed by that surface divided by the permittivity of the medium. This law can be applied to a conductor with an arbitrary shape by considering the charge enclosed by a small surface element and summing up the contributions from all elements to find the total electric field.

3. What factors affect the strength and direction of the electric field for a conductor with an arbitrary shape enclosing charge?

The strength and direction of the electric field for a conductor with an arbitrary shape enclosing charge are affected by the magnitude and distribution of the charge, as well as the shape and size of the conductor. The distance from the charge also plays a role, as the electric field decreases with distance.

4. How does the presence of a conductor with an arbitrary shape enclosing charge affect the electric field in its surroundings?

The presence of a conductor with an arbitrary shape enclosing charge can significantly alter the electric field in its surroundings. The charge on the conductor will repel or attract other charges, causing the electric field lines to bend and distort near the conductor. The shape of the conductor also determines the direction and magnitude of the electric field at different points in space.

5. How can the "E field of a conductor with an arbitrary shape enclosing charge" be visualized?

The "E field of a conductor with an arbitrary shape enclosing charge" can be visualized using electric field lines. These lines represent the direction and strength of the electric field at different points in space. The density of the lines indicates the strength of the field, with closer lines representing a stronger field. The direction of the lines shows the direction in which a positive test charge would move if placed in the field.

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