Potential of a spherical shell (non-uniform charge density)

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Homework Help Overview

The discussion revolves around a problem involving a spherical shell with a non-uniform surface charge density, where participants are tasked with finding the electric potential and electric field both inside and outside the sphere. The original poster expresses confusion regarding the setup and the implications of the charge distribution.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to understand the implications of the charge distribution and its effect on the potential and electric field. Some participants question the absence of a specific equation relating to charge density in the problem statement, suggesting the need for additional information or context. Others explore the idea of treating the charge distribution as a point charge, while noting potential contradictions regarding the total charge being zero due to the distribution of positive and negative charges.

Discussion Status

The discussion is ongoing, with participants raising questions about the problem's setup and the implications of the charge distribution. There is no explicit consensus yet, but some guidance is being offered regarding the need for further clarification on the charge density and its role in the calculations.

Contextual Notes

Participants are grappling with the lack of a clear equation for charge density and its impact on the electric potential and field. The original poster's diagram is mentioned, but its effectiveness in clarifying the problem is uncertain. There is also a discussion about the conditions under which the cosine of the angle becomes negative, indicating a need for deeper exploration of the geometry involved.

SquidgyGuff
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Homework Statement


Given a spherical shell of radius R and the surface charge density
gif.gif
(
gif.gif
being the angle from the top of the sphere
gif.gif
and
gif.gif
being a constant) find the electric potential
gif.gif
and the electric field
gif.gif
inside and outside the sphere. Check that both the potential is continuous inside and outside the sphere and that
gif.gif
inside and out. I made this little diagram to illustrate.
sphere_by_k4l3b-d98wxw3.png


2. Homework Equations

gif.gif

gif.gif


The Attempt at a Solution


I can't even understand this problem. I feel like the point of interest shown in the diagram should be on the shell so that
gif.gif
can return a meaningful value, but I need to find the potential and electric field everywhere, so it can't be on the sphere.
 
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Hello Guff,

I notice that your problem statement mentions a charge distribution on the surface of the sphere, but that there is no equation where charge or charge density plays a role. Is there something you can add to your 'toolbox' ?
 
BvU said:
Hello Guff,

I notice that your problem statement mentions a charge distribution on the surface of the sphere, but that there is no equation where charge or charge density plays a role. Is there something you can add to your 'toolbox' ?
If I looked at the charge distribution a point charge the field would look like this
%5Cfrac%7B%28%5Csigma_%7B0%7Dcos%5Ctheta%29%284%5Cpi%20R%5E%7B2%7D%29%7D%7Br%5E2%7D%5Chat%7Br%7D.gif
, but I know that isn't correct because I believe the total charge is zero. because half of the values of
gif.gif
are negative and the other half are positive.
 
I still don't see how you want to find the field or the potential at a point in space.
Where exactly on the sphere is ##\cos\theta## negative ?
 

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