Charging and Discharging of two capacitors

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Discussion Overview

The discussion revolves around the charging and discharging behavior of two capacitors with different capacitances and voltages when connected in various configurations. Participants explore the physical principles underlying charge summation and cancellation in these scenarios, as well as the role of electrons in charge flow.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant states that when connecting capacitors with similar terminals, the net charge is the sum of the individual charges, while connecting opposite terminals results in the net charge being the difference of the individual charges.
  • Another participant emphasizes the importance of tracking signs when adding charges, noting that positive charges are summed directly, while positive and negative charges are combined with subtraction.
  • Several participants inquire about the physical mechanisms behind charge addition and cancellation, particularly in relation to electron movement and redistribution.
  • One participant mentions that the segments connecting the capacitor plates have negligible charge compared to the capacitors themselves, and that any potential difference prior to connection is equalized by a transient flow of charge.
  • Another participant explains that electrons redistribute themselves until equilibrium is achieved when the capacitors are connected.
  • Some participants provide examples involving excess and deficiency of electrons on metal bits, illustrating how these charges combine when connected.
  • A later reply suggests that the explanation provided offers a 'quantum explanation' for the problem, indicating a more nuanced understanding of the charge interactions.

Areas of Agreement / Disagreement

Participants generally agree on the principles of charge summation and cancellation, but there are varying interpretations of the underlying physical processes, particularly regarding electron behavior and the significance of connecting segments.

Contextual Notes

Some assumptions about charge distribution and the role of connecting segments remain unaddressed, and the discussion does not resolve the complexities of electron interactions in the context of capacitor behavior.

Hijaz Aslam
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Two capacitors with different capacitance are charged with two different voltages. When we connect both the capacitors with the similar terminals (that is positive terminal of one capacitor to the positive terminal of the other and vice-versa) the net charge is the sum of the former individual charges.

Whereas when we connect both the capacitor (without any battery or cell in the circuit) with the opposite terminals (that is positive terminal of one capacitor connected to the negative of the other and vice-versa) the net charge is taken as the difference of the former individual charges of both the capacitors.

Physically how does this happen?
 
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When the terminals are connected together, the net charge is always the sum of the original charges, but you must keep track of the signs. In one case, you are adding positive charges together, Q1+Q2; in the other case, you are adding positive charges to negative charges, so it looks like Q1 + -Q2 = Q1 - Q2.
 
Physically how does this happen?

Like charges are cumulative.
Opposite charges cancel each other.
 
Alright, so when we connect the capacitors the segment which connects each plates adds up or cancels out according to the connection?
But how does this happen in terms of the electrons which are the basic constituents that contributes to the charge flow?
 
Hijaz Aslam said:
Alright, so when we connect the capacitors the segment which connects each plates adds up or cancels out according to the connection?
But how does this happen in terms of the electrons which are the basic constituents that contributes to the charge flow?
The segments' charges and capacities are negligible compared to capacitors' charges and capacities.
If there is a potential difference between segments prior to the series connection of the caps, small equalizing electrical transient takes care of it.
 
Hijaz Aslam said:
Alright, so when we connect the capacitors the segment which connects each plates adds up or cancels out according to the connection?
That's right.

Hijaz Aslam said:
But how does this happen in terms of the electrons which are the basic constituents that contributes to the charge flow?
The electrons are free to redistribute themselves until equilibrium is reached.
 
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If you have an excess of 2000 electrons (eg a -ve charge) on one bit of metal and an excess of 1000 on another then when you connect them together you have an excess of 2000 + 1000 = 3000 electrons.

If you have an excess of 2000 electrons on a bit of metal and a deficiency of 1000 (eg a +ve charge) on another then when connected you have of 2000 + (-1000) = 1000.
 
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CWatters said:
If you have an excess of 2000 electrons (eg a -ve charge) on one bit of metal and an excess of 1000 on another then when you connect them together you have an excess of 2000 + 1000 = 3000 electrons.

If you have an excess of 2000 electrons on a bit of metal and a deficiency of 1000 (eg a +ve charge) on another then when connected you have of 2000 + (-1000) = 1000.

I think that gives a sort of 'quantum explanation' for the problem.
Thanks for your support everyone!
 

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