Dialectric inserted into capacitor => creation of a double-capacitor

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Discussion Overview

The discussion centers around the effects of inserting a dielectric into a capacitor, specifically how it influences the behavior of the capacitor and the resulting capacitance. Participants explore the theoretical implications of this configuration, including the concept of capacitors in series and the role of induced charges.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions how a dielectric can develop induced charges equivalent to those on the capacitor plates, suggesting that this expectation may be unfounded.
  • Another participant proposes that adding a conducting plate of negligible thickness between the dielectric and air would not change the overall capacitance, indicating that the situation can be viewed as two capacitors in series.
  • A claim is made that a dielectric in series results in equal charges on all plates, prompting a question about why this does not apply to the current dielectric scenario.
  • One participant explains that inserting a dielectric changes the permittivity between the plates, which in turn alters the capacitance, allowing for selection of capacitance based on the dielectric material used.
  • Another participant discusses the potential gradient across the air gap versus the dielectric, suggesting that the presence of the dielectric leads to different potential gradients, akin to two capacitors in series sharing the total potential difference.
  • A correction is made regarding the spelling of "dielectric," along with a clarification on its role as a non-conductive layer between capacitor plates and its impact on capacitance based on thickness and composition.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of the dielectric and its effect on charge distribution and capacitance. There is no consensus on the implications of inserting a dielectric or the nature of induced charges.

Contextual Notes

Participants mention various assumptions regarding the behavior of dielectrics and capacitors, including the effects of thickness and material composition, but these assumptions remain unresolved within the discussion.

Nikitin
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A dialectic of width d is inserted into a capacitor made up of two plates, with the plates being a distance D apart. D>d. Afterwards, the capacitor acts like it is two capacitor connected in series. Why? I mean how the heck is the dialectic supposed to get induced charges equivalent to the ones on the capacitor-plates?

the situation is illustrated in the solution manual. Look for assignment 4b ("Oppgave 4 b", page 4) http://folk.ntnu.no/sveinoll/ov/TFY/4155%20Elektrisitet%20og%20Elektromagnetisme/V11/LF/Ov06los.pdf . The situation as described is like A, and the capacitor acts like in B.
 
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I mean how the heck is the dialectic supposed to get induced charges equivalent to the ones on the capacitor-plates?
It is not, why do you expect this?

You can imagine adding an additional conducting plate of "0" thickness between the dielectric and the air (or whatever) without changing the capacity. But then you just have two different capacitors in series.
This is possible without dielectric, too, by the way.
 


A dialectric in series has equal charges on all the plates. Why doesn't this dialectric have that?
 


I'm not 100% certain what your question is. But putting a dielectric in-between the plates causes the permittivity in-between the plates to change. And this means that the capacity of the capacitor will change. So by selecting a material of a certain permittivity, you can choose the capacitance of the capacitor. pretty neat.
 


With or without a layer of metal between the dielectric and the air, I think the same situation exists. There will be a potential gradient across the air gap and a different (shallower) potential gradient across the dielectric because the molecules of the dielectric can polarise. It's just like two capacitors in series, sharing the total PD. The equivalent capacitance will be greater than for an air gap and less than when full of dielectric.
 


Nikitin said:
A dialectric in series has equal charges on all the plates. Why doesn't this dialectric have that?

its spelt ... Dielectric :)

It seems you don't realize or understand what a dielectric is
its the non-conductive layer between 2 plates of a capacitor
it may be composed of air, paper or ceramic amongst other things

The thickness and composition of which, as others have said, will have an effect on the value of capacitance


Dave
 

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