Cylindrical Capacitor

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Homework Help Overview

The discussion revolves around a problem related to cylindrical capacitors, specifically focusing on determining the radius of a cylinder that contains half of the stored electric potential energy. The original poster mentions using the capacitance formula for a cylinder and expresses difficulty with the charge variable in the context of energy equations.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the need for clarity on the problem statement and the equations used. The original poster attempts to apply the capacitance formula and energy equations but encounters challenges with the charge variable. There are mentions of using integrals related to electric potential energy.

Discussion Status

The conversation is ongoing, with participants seeking more details about the problem and the original poster's attempts. Some guidance has been offered regarding the need for specificity in the question and the equations used, but no consensus or resolution has been reached.

Contextual Notes

The original poster notes that the assignment deadline has passed, indicating a potential constraint on the urgency of the discussion. There is also mention of a visual aid (a picture of the cylindrical capacitor) that may be relevant to understanding the problem setup.

rey242
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Homework Statement


Hey guys, My prof asked us to find the radius of a cylinder within a cylindrical capacitor with 2 radii a and b. I know we use the Capacitance formula for a cylinder but I can't seem to get pass the q that shows up when I plug it into the 1/2 c*V^2

EDIT: He wants us to find a cylinder's radius that contains half the stored electric potential energy.
 
Last edited:
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I'm afraid you'll need to be a lot more specific than that. Can you give us the full question (word-for-word), plus all of the equations you used and all of the calculations you tried?
 
Oh I'm sorry, I forgot to add something. He wants us to find a cylinder's radius that contains half the stored electric potential energy.

Yea there's a picture he showed us, a long cylindrical capacitor. The picture shows a cross section of the cylinder. The smaller cylinder within the bigger one has a radius a and the bigger one has a radius b. The radius of an arbitrary cylindrical Gaussian surface between a and b is r.

I tried to use C= 2pi E0 (L/ ln(b/a)) for the capacitance and use it with both forms of Electric Potential energy equation(q^2/r and 1/2cV^2). But I get stuck on the charge q variable. and I even tried to use the Integral used to derive Elec. Potent. Eng. but I can't really figure that out what to do with that.
 
Even though the homework assignment passed, I would still like an answer to this. :)
 

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