Why Do Capacitors Accumulate Charge?

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Discussion Overview

The discussion revolves around the mechanisms of charge accumulation in capacitors, exploring the underlying principles of how and why charge builds up on the plates. Participants delve into concepts related to energy states, electron flow, and analogies to static electricity and water systems.

Discussion Character

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

Main Points Raised

  • Some participants question why charge accumulates on capacitor plates and whether this represents a higher energy state compared to a battery.
  • Others argue that charge accumulation occurs until the energy per electron is equal on both sides, suggesting that the capacitor does not reach a higher energy state than the battery.
  • A participant expresses confusion about electron flow when the circuit is open, questioning the conditions under which electrons should flow.
  • Another participant clarifies that the circuit is considered "open" only when the capacitor is fully charged, and current flows until the voltage across the plates equals the applied voltage.
  • One participant draws an analogy between capacitors and static electricity, explaining how charge imbalances create electric fields and current flow between the plates.
  • A further analogy compares a capacitor to a water tower, illustrating the concept of charge and voltage in terms of water flow and pressure.

Areas of Agreement / Disagreement

Participants express differing views on the energy states of capacitors and the conditions for electron flow, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

Some assumptions about charge behavior, energy states, and analogies may not be fully articulated, leading to potential gaps in understanding the underlying physics.

Avichal
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After studying more complicated electronics, I find myself asking this question - 'Why capacitor works?'
Why does charge get accumulated on the plates? Isn't that a higher energy state than battery?
 
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Why does charge get accumulated on the plates?
Opposite charges attract each other, and the other side has the opposite charge.
Isn't that a higher energy state than battery?
No, the capacitor gets charged until the energy per electron is the same in both.
 
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mfb said:
No, the capacitor gets charged until the energy per electron is the same in both.

Why is it not a higher energy state? When the circuit is closed I understand why electrons flow. But when it is open(which is in this case), I don't understand why electrons should flow.
 
Avichal said:
Why is it not a higher energy state? When the circuit is closed I understand why electrons flow. But when it is open(which is in this case), I don't understand why electrons should flow.

The circuit is only "open" when the capacitor is fully charged. Until then current will flow into one plate and out of the other until the voltage drop across the plates is equal to the applied voltage.
 
If you are familiar with static electricity you will know that it's possible for an object like a plastic comb or rod to become charged up (eg it acquires a surplus or shortage of electrons). Much the same thing happens with each plate of a capacitor...

Imagine one plate (lets call it the top plate) behaves like a comb that you have charged up with extra electrons. If that top plate is close to another plate (eg the bottom plate) then the electrons in the top plate will repel electrons in the bottom plate (like charges repel remember). The electrons in the bottom plate will try to move away from the top plate by escaping down the wire.

So now you have electrons on the top plate and a shortage of electrons on the bottom plate... and for awhile you had current flowing. You put electrons into the top plate and different electrons left the bottom plate.

If you have electrons on one plate and a shortage on the other then there will be an electric field/ voltage between the two plates. This voltage will build up until it's greater than the voltage that caused the surplus of electrons on the top plate. At that point no more electrons flow onto the top plate or out of the bottom plate.
 
A capacitor is somewhat analogous to a water tower. You can pump water in, then close off the gate. Later, you can open the gate and water will flow out. Now replace water with charge, and water pressure with voltage.
 

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