Negative potential energy and capacitors

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Discussion Overview

The discussion revolves around the concept of negative potential energy in the context of capacitors, particularly parallel plate capacitors. Participants explore how the attraction between oppositely charged plates relates to energy storage and the implications of defining potential energy in different ways.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the attraction between oppositely charged plates in a capacitor implies that they store negative energy, suggesting this could lead to incorrect conclusions about energy storage.
  • Another participant notes that potential energy is defined up to an additional constant, indicating that the definition may not be absolute.
  • A participant presents a scenario analyzing the energy states of parallel plates with different distances, proposing that depending on the reference point chosen for zero energy, the potential energy can be either negative or positive.
  • Discussion includes methods of extracting energy from a capacitor, highlighting how the movement of charges affects the energy associated with the capacitor and referencing the importance of zero as a reference point in potential energy definitions.

Areas of Agreement / Disagreement

Participants express differing views on the implications of negative potential energy in capacitors, with no consensus reached on whether it leads to incorrect interpretations of energy storage.

Contextual Notes

Participants reference different conventions for defining zero potential energy, which may affect their interpretations and conclusions about energy states in capacitors.

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potential energy is defined up to an additional constant by the way
 
Say parallel opposite charges plates whose distance d are:

1. infinite
2. finite ##d_0##
3. 0 and all electrons and positive ions on the plate reunite after releasing energy with short circuit.

Then energy of the states are
E_3<E_2<E_1

If we take ##E_1=0## as you do for gravity, ##E_2## is negative.

If we take ##E_3=0## as usually we do in electric circuit studies, ##E_2## is positive.
Even in gravity study, we have learned that a object of mass m in height h has potential energy ##mgh >0##.
 
We can take energy out of a capacitor by:

1. Letting the positive charges move further apart. That decreases the positive energy of one plate.
2. Letting the negative charges move further apart. That decreases the positive energy of one plate.
3. Letting the opposite charges get closer together. That increases the negative energy of the capacitor.
4. Draining the capacitor, which involves all those three things above.In the link in post #1, there it is mentioned something about zero being a special number among numbers, and gravitational potential at infinity being a special gravitational potential among gravitational potentials. Well, I agree with that part of the answer. (Actually only zero being an important number was mentioned. Well, it's not a very good answer IMO)
 
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