Doubt in parallel plate capacitor

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Discussion Overview

The discussion revolves around the behavior of electric fields in a parallel plate capacitor, specifically addressing misconceptions about the direction of electric fields produced by the plates and their cancellation effects both inside and outside the capacitor. Participants explore theoretical aspects, including Gauss's law and the principle of superposition, while examining images of electric fields around capacitors.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about which electric fields are in opposite directions and how they cancel out, questioning if this is true only for equal charges on the plates.
  • Another participant suggests considering the fields produced by each plate independently and then applying the principle of superposition to understand the resultant fields.
  • Some participants discuss the distinct behavior of electric fields inside the capacitor versus outside, noting that the electric field inside the plates cancels out due to the opposing directions of the fields from the positive and negative charges.
  • There is a challenge regarding the assertion that the electric field outside the capacitor is zero, with participants emphasizing the need to consider the directions of the fields produced by the charges.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as there are competing views on the behavior of electric fields in different regions of the capacitor and the implications of charge direction on field cancellation.

Contextual Notes

Some participants reference Gauss's law and the principle of superposition, but there are unresolved assumptions regarding the conditions under which the electric fields cancel and the implications of charge distribution.

AdityaDev
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I was going through the capacitor lesson in my textbook. In it its written "...both positive and negative plates will produce electric field in the same direction, hence the electric field adds up...outside the plates, electric field is zero since the field due to negative and positive charges are in opposite direction..."
My doubt : i am confused at the 2nd statement. (i have attached two images)
  • which electric fields are in opposite direction? how does it cancel out?
  • Is this true only if the charge on the capacitor plates are same?
  • Do electric fields extend to infinity?
  • does the electric field outside capacitor for second image become zero?
 

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What do you think, and why? Then we can correct the specific misconceptions that you have.
 
jtbell said:
What do you think, and why? Then we can correct the specific misconceptions that you have.
this is what I think... let the positive plate be on the left and the negative on right. From gauss law, field inside conductor should be zero. Maybe the positive field from left plate extends to right and the negetive from right plate also passes through plate 1 on ...I have no idea...
 
Have you looked at images of the fields around a parallel plate capacitor? The situation between the plates is very distinct from the situation outside and at a distance.
This link shows what happens outside.
 
AdityaDev said:
and the negetive from right plate also passes through plate 1

You're on the right track here. Do you know about the principle of superposition? Consider the field produced by each plate by itself, as if the other one were not there at all; then add the two fields together.
 
Last edited:
sophiecentaur said:
Have you looked at images of the fields around a parallel plate capacitor? The situation between the plates is very distinct from the situation outside and at a distance.
This link shows what happens outside.
you are going off topic
 
jtbell said:
You're on the right track here. Do you know about the principle of superposition? Consider the field produced by each plate by itself, as if the other one were not there at all; then add the two fields together.
Ok.field of -Q charge from the inner surface of left plate passes through the metal plate. the electric field of +Q charge also passes through its own metal plate. Hence inside the metal plate the electric field cancels out. This also happens outside the plate. Hence there also field cancels out.
 
AdityaDev said:
Hence inside the metal plate the electric field cancels out.

No... consider the directions of the two fields. The electric field produced by a positive charge points away from the charge, and the electric field produced by a negative charge points towards the charge.
 
jtbell said:
No... consider the directions of the two fields. The electric field produced by a positive charge points away from the charge, and the electric field produced by a negative charge points towards the charge.
That is why it cancels out int outer region. One is in +x and other is in -x. But inside both are in same direction.
 
Last edited by a moderator:
  • #10
O
jtbell said:
No... consider the directions of the two fields. The electric field produced by a positive charge points away from the charge, and the electric field produced by a negative charge points towards the charge.
Oops... Outside the metal plate E cancels out
 

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