Cylindrical Capacitor

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SUMMARY

The discussion centers on calculating the radius of a cylindrical capacitor that contains half of the stored electric potential energy. The relevant capacitance formula used is C = 2πE₀(L/ln(b/a)), where E₀ is the permittivity of free space, L is the length of the cylinder, and a and b are the inner and outer radii, respectively. The challenge arises from the charge variable q in the electric potential energy equations, specifically q²/r and 1/2 C V². Participants emphasize the need for clarity in the problem statement and the equations involved to derive the solution effectively.

PREREQUISITES
  • Cylindrical capacitor theory
  • Capacitance formula for cylindrical geometries
  • Electric potential energy equations
  • Understanding of Gaussian surfaces in electrostatics
NEXT STEPS
  • Study the derivation of electric potential energy in capacitors
  • Learn about Gaussian surfaces and their applications in electrostatics
  • Explore the relationship between charge, capacitance, and voltage in cylindrical capacitors
  • Investigate numerical methods for solving integrals related to electric potential energy
USEFUL FOR

Students in physics or electrical engineering, particularly those studying capacitors and electric potential energy calculations, will benefit from this discussion.

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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