Electric potential in an open circuit

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Discussion Overview

The discussion revolves around the behavior of capacitors in an open circuit, specifically addressing whether an uncharged capacitor can have a potential difference and charge when the circuit is not closed. Participants explore theoretical implications and practical observations related to electric potential in such scenarios.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that if a capacitor is uncharged and placed in an open circuit, its potential difference and charge would be zero.
  • Others argue that an uncharged capacitor does not acquire a charge regardless of whether the circuit is open or closed, maintaining zero electric potential.
  • A later reply challenges the conventional understanding, suggesting that a capacitor can charge in an open circuit if one plate is connected to an external source of free charges, such as static electricity.
  • One participant mentions the concept of the Avramenko plug, indicating that it is possible for a capacitor to charge without a closed circuit if certain conditions are met.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of capacitors in open circuits, with no consensus reached regarding the potential difference or charge of an uncharged capacitor in such a configuration.

Contextual Notes

Some claims rely on specific experimental setups or definitions of electric potential that may not be universally accepted, highlighting the need for further investigation into the behavior of capacitors in open circuits.

yoyoloto
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Hi,

I was wondering, if a circuit is open, would capacitors still have a potential difference ?
If there is no potential difference, can we say its potential is 0 then obtain a charge equal to 0 for the capacitor's charge ?
 
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What I meant is that the capacitor isn't charged in the first place, the circuit is all set up and stuff but its never closed, therefore no current. So I don't think there could be any potential either, making its charge 0.
 
hi yoyoloto! :smile:

(just got up :zzz: …)
yoyoloto said:
What I meant is that the capacitor isn't charged in the first place, the circuit is all set up and stuff but its never closed, therefore no current. So I don't think there could be any potential either, making its charge 0.

oh i see!

ok, then yes, if the https://www.physicsforums.com/library.php?do=view_item&itemid=112" is uncharged, and placed into an open circuit, the potential difference (voltage) across it will remain zero, an so will the charge :smile:
 
Last edited by a moderator:
If the capacitor is uncharged, then it doesn't matter if the circuit is closed or open, the electric potential is zero. An uncharged capactor by itself is also zero electric potential.
 
The problem with schooling today. Typically, the answer is no. The capacitor will not acquire a charge connected to an open circuit and the student may build a simple lab circuit to reinforce this claim as taught. Allowing them to chug along with no further investigations with open potentials. Which is very misleading. I would encourage the student to further explore the open potential as follows and see what results you get.
Connect the capacitor across an open voltage but also connect a aerial to one plate only. Single wire. The cap will chargeup while drawing zero current from the source supply. Aka avramenko plug.
Any capacitor connected to an open voltage will indeed. Charge up so long as one of the plates has Access to free charges, including static charges along the surfaces but not closed loop back to your circuit. Remains electrically an open circuit from the source supply. Another way is an open voltage single wire with diode block to a cap and it's tank circuit closed by a spark gap. The output closed ckt having a single Earth connection but input driving side is open to the output ckt. Power can be produced via potential alone and has already been demonstrated all over the world and there are numerous patents on this technique.
 

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