Capacitance, parallel plates, electric field

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Homework Help Overview

The discussion revolves around calculating the capacitance of parallel plates and understanding the electric field in this context. The original poster is exploring the use of Gauss's law and is uncertain about the appropriate Gaussian surface to use, particularly questioning whether a spherical surface would be suitable given the non-infinite nature of the plates.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to determine the electric field using Gauss's law and questions the choice of Gaussian surface. They also raise a separate question regarding the potential limits for concentric spheres with charges.

Discussion Status

Some participants suggest assuming the plates are infinite for simplification, while others clarify that the area used in the capacitance formula is relevant but may not depend on the specific shape of the plates. The discussion is exploring different interpretations of the problem without reaching a consensus.

Contextual Notes

Participants are considering the implications of plate size and shape on the calculations, as well as the effects of fringe fields, which may not be fully defined in the original problem statement.

Chronos000
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Homework Statement



To find the capacitance of parallel plates, I am first finding the E field using gauss. However I don't know what the gaussian surface will be. I don't think it will be a gaussian pillbox as the plates aren't infinite, but will it be a sphere??

On a side note, if I have two concentric spheres with radii a<b with charges +Q and -Q, what are the limits of the potential: My thoughts were: b is final, a is initial
 
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Assume the plates are infinite if the plates are very close together. Ignore fringe effects.
 
in that case, do you know if the area quoted in the capacitance for parallel plates is the area of a circle, and not that of a square/rectangle?

( C= A*epsilon/d )
 
Doesn't matter. It's just the area of your pillbox. It'll cancel.
 

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