How does a capacitor get charged?

  • Context: High School 
  • Thread starter Thread starter krackers
  • Start date Start date
  • Tags Tags
    Capacitor Charged
Click For Summary

Discussion Overview

The discussion centers on the charging process of a parallel-plate capacitor, exploring the movement of electrons and the role of a connected battery. Participants examine the initial state of the capacitor, the effects of connecting the battery, and the resulting charge distribution on the plates.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants describe the initial state of the capacitor as having equal positive and negative charges on both plates.
  • It is noted that when the battery is connected, electrons from the top plate move towards the positive terminal, leading to a positive charge on the top plate.
  • Questions arise regarding the destination of the electrons after they leave the top plate and how the bottom plate becomes negatively charged.
  • One participant suggests that electrons from the negative terminal of the battery move towards the bottom plate, charging it negatively.
  • Another participant questions the source of the negative pole and whether electrons would be repelled from a neutral plate, raising concerns about the movement of electrons towards the bottom plate.
  • Further explanations include that electrons from the electrolyte near the battery's negative terminal migrate to the bottom plate, contributing to its negative charge.
  • Some participants mention the electric fields created by the charge separation and the battery, which help maintain the charge on the capacitor.
  • There are references to the electrochemistry of the battery, although some participants argue that it does not directly influence the capacitor's charging process.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms of electron movement and the implications of the battery's electrochemistry. There is no consensus on the specifics of how the bottom plate becomes negatively charged or the role of the battery in this process.

Contextual Notes

Some assumptions about the behavior of electrons and the nature of electric fields are not fully explored. The discussion also touches on electrochemical processes that are not directly related to the capacitor's operation.

Who May Find This Useful

This discussion may be of interest to those studying electrical engineering, physics, or anyone seeking to understand the principles of capacitors and their charging mechanisms.

krackers
Messages
72
Reaction score
0
[I have attached a diagram of the setup below].

I am trying to understand how exactly a parallel-plate capacitor [the one with two metal plates separated by a dielectric] gets charged. This is what I have gotten so far.

1) When the capacitor is in its uncharged state, both metal plates have both positive and negative charges in equal amounts.

2) When the battery is connected, the electrons in the top plate move towards the positive terminal of the battery.

3) ? Where does the electron go now?

4) The electrons in the top plate keep moving moving towards the positive terminal, making the top plate positively charged.

5) How does the bottom plate become negatively charged?
 

Attachments

  • Untitled.png
    Untitled.png
    1.4 KB · Views: 644
Physics news on Phys.org
The electrons all along the wire are set into motion when the battery is connected. Those close to the top plate tend to move away from it thus the plate is charged positive. Respectively the electrons on the bottom part of the wire are repelled by the negative pole and move in the direction of the bottom plate where they stack, charging it negatively.
 
Trifis said:
The electrons all along the wire are set into motion when the battery is connected. Those close to the top plate tend to move away from it thus the plate is charged positive. Respectively the electrons on the bottom part of the wire are repelled by the negative pole and move in the direction of the bottom plate where they stack, charging it negatively.

What is the source of the negative pole? Further, if the bottom plate is neutral, why would electrons move towards it. Wouldn't they get repelled, since the neutral plate contains electrons as well?
 
Last edited:
How does the battary work is another topic... Just consider that the two poles function in a reverse manner, the positive attracts and the negative repells. Thus the electrons on the top are moving away from the plate while those in the bottom are moving towards it, cause they are being repelled by the negative pole.
 
krackers said:
[I have attached a diagram of the setup below].

I am trying to understand how exactly a parallel-plate capacitor [the one with two metal plates separated by a dielectric] gets charged. This is what I have gotten so far.

1) When the capacitor is in its uncharged state, both metal plates have both positive and negative charges in equal amounts.

2) When the battery is connected, the electrons in the top plate move towards the positive terminal of the battery.

3) ? Where does the electron go now?

4) The electrons in the top plate keep moving moving towards the positive terminal, making the top plate positively charged.

5) How does the bottom plate become negatively charged?

3) The electron from the top plate when it reaches the positive electrode of the battery combines with a positive ion (i.e., cation) in the electrolyte that surrounds that electrode. What happens next is described by the electrochemistry of that battery. However, it really doesn't matter to the capacitor. The top plate now has more protons than electrons, so it is positively charged.

5) Electrons leave the negative ions (i.e., anions) in the electrolytic solution near the negative electrode of the battery. The details again have to do with the electrochemistry of the battery. However, electrochemistry does not directly influence the capacitor.
The electrons move into the metal on the bottom plate. The bottom plate now has more electrons than protons, so that it is negatively charged.

There is an electric field in the dielectric of the capacitor that points from the top plate to the bottom plate. Therefore, the extra protons in the top plate attract the extra electrons in the bottom plate. This attraction helps keep the capacitor charged.
There is also an electric field from the positive terminal to the negative terminal of the battery. This also helps keep the capacitor charged.

A more detailed description would require a solid state description of both the metal and dielectric of the capacitor, in addition to the electrochemistry of the battery.
 
The electrons then exit the negative battery terminal and migrate to the negative plate.
 

Similar threads

Undergrad Charging Capacitor with one terminal grounded
  • · Replies 16 ·
Replies
16
Views
3K
Undergrad Parallel plate capacitor, charge imbalance VS charge redistribution
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Capacitor surface charge movement current, relativistic effects
  • · Replies 2 ·
Replies
2
Views
2K
High School Do Electrons Completely Leave a Capacitor at T/4 in an LC Circuit?
  • · Replies 2 ·
Replies
2
Views
873
High School Some Questions about Electric Current/Capacitors to help my understanding
  • · Replies 7 ·
Replies
7
Views
2K
High School Rotating Capacitor: Concentrating energy using accessible technology
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Is capacitor energy the electrostatic energy of the whole system?
  • · Replies 9 ·
Replies
9
Views
2K
Undergrad Magnetic field when the area of the plates of a capacitor increases
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Voltage drop across a capacitor and resistor in series
  • · Replies 19 ·
Replies
19
Views
5K
High School How is capacitor energy the same as electrostatic potential energy?
  • · Replies 21 ·
Replies
21
Views
2K