Finding electric field through capacitor

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Discussion Overview

The discussion revolves around calculating the electric field in a parallel-plate capacitor that contains two different dielectrics when a voltage is applied. Participants explore the relationship between electric field, voltage, and dielectric properties, focusing on the implications of the capacitor's configuration.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant presents a scenario involving a parallel-plate capacitor with two dielectrics and asks how to divide the voltage between them.
  • Another participant suggests starting with the electric displacement field D and questions the relevance of the width of the dielectrics.
  • A participant provides the relationship between the electric displacement field and the electric field, indicating that the electric field can be derived from D and the permittivity.
  • There is a mention of the formula for the displacement field, which is related to charge and area.
  • Participants express gratitude for shared formulas and insights regarding the displacement field's units.

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to approach the problem of voltage division between the dielectrics, and the discussion remains exploratory with multiple viewpoints presented.

Contextual Notes

Participants do not clarify certain assumptions regarding the relationship between the electric field and the displacement field, nor do they resolve how to apply the voltage across the two dielectrics specifically.

geft
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A parallel-plate capacitor with two dielectrics is placed in a circuit with 10V applied.

Dielectric A has 0.001m width and relative permittivity 2. Dielectric B has 0.003m width and relative permittivity 4. The plates have area of 0.01m^2. What is the electric field through each dielectric? (Ans: 4000 V/m and 2000 V/m)

I know the formula used is E = V/d, but how do I divide the voltage between these dielectrics?
 
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hi geft! :smile:
geft said:
I know the formula used is E = V/d, but how do I divide the voltage between these dielectrics?

why would the width matter?

start with the electric displacement field D …

what is its magnitude, and how is E related to it? :wink:
 
D = eE

E = D/e = V/d

...but I wouldn't be able to get the displacement field without the electric field, right?
 
displacement field was invented for the capacitor …

D = -Q/A :wink:​
 
Didn't know that formula, thanks! :)
 
oooh, i forgot to mention …

that's exactly why the electric displacement field D is measured in units of coulombs per square metre, C/m2 :biggrin:​
 

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