How would this capacitor configuration work?

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Discussion Overview

The discussion revolves around the behavior of charges on capacitor plates when different dielectrics are present between them. Participants explore the implications of dielectric polarization, charge distribution, and electric fields in this configuration, addressing both theoretical and conceptual aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the charges on the plates remain uniformly distributed when two different dielectrics are present, suggesting that this could lead to a varying potential difference across the capacitor.
  • Another participant asserts that conductors are always equipotential, indicating that the dielectrics become polarized in the direction of the electric field, which affects charge density near the conductors.
  • A participant seeks clarification on the distribution of charge on a conducting plate, noting that while charge is uniformly distributed in isolation, the presence of dielectrics complicates this, leading to a non-zero electric field from surface charges.
  • One participant cautions against assuming uniform charge distribution for isolated conductors, emphasizing the need to consider charge density and the assumption of constant voltage when analyzing such systems.

Areas of Agreement / Disagreement

Participants express differing views on the uniformity of charge distribution in the presence of dielectrics, with some suggesting non-uniform distribution while others emphasize the equipotential nature of conductors. The discussion does not reach a consensus on these points.

Contextual Notes

There are unresolved assumptions regarding the behavior of charges in the presence of dielectrics and the conditions under which uniform charge distribution can be assumed. The discussion also highlights the complexity of electric fields in non-homogeneous materials.

Who May Find This Useful

This discussion may be of interest to those studying electrostatics, capacitor design, and the effects of dielectric materials in electrical engineering or physics contexts.

azure kitsune
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Assume you have two parallel plates with charges +q and -q.

Now, you fill the space in between with two different dielectrics so that if you were to move straight from one plate to the other, you would be in the same dielectric. (In other words, the two dielectrics do not form "layers.")

My question is: What happens to the charges on the plates?

Do they stay uniformly distributed? This would mean the potential difference across the capacitor is different at different locations. Wouldn't this make the electric field inside the capacitor non-conservative?

Do the charges move reposition themselves so that the potential difference remains constant? If this were true, wouldn't the charges have a tendency to go back to uniform distribution because the closer-packed ones would repel each other more?

If the capacitor is connected to an EMF source with constant voltage, then I believe the charges would reposition themselves to maintain the same potential drop. But what if there is no current?
 
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The conductors will always be equipotential, due to E = 0 inside the conductor. The dielectrics are polarized in the direction of E, which means there is an effective charge density next to each conductor. This allows the charge inside the conductor to be re-arranged.
 
Thank you for explaining! I think I understand. Is the following statement correct?:

For a charged conducting plate by itself, the charge would be uniformly distributed on the two surfaces because there is no other way for E to be 0 inside. For a capacitor with two dielectrics, the charge is not uniformly distributed, so the electric field inside the plate due to the charges on the surface alone is not zero. However, the net electric field inside the conductor (which includes E from the polarized dielectrics) is zero.
 
It's not really safe to assume charge is distributed uniformly, even for isolated conductor. Except perhaps spheres or infinite plates. You usually start with the assumption of a constant voltage on the conductor, and then solve for the charge density.
 

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