Condensers connected in series

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Discussion Overview

The discussion revolves around the behavior of capacitors (condensers) connected in series, specifically addressing the charge distribution on the plates and the effects of inserting a dielectric. Participants explore the underlying principles and seek intuitive explanations for these phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • Some participants question why one plate (a) gets a +Q charge while the other plate (b) gets -Q, suggesting that the total charge must balance to zero.
  • Others discuss the implications of inserting a dielectric, proposing that it alters the charge distribution and leads to behavior akin to two capacitors in series.
  • A participant mentions that charge imbalance occurs due to thermal agitation and that applying voltage causes charge migration, influencing the charge on the plates.
  • One participant emphasizes that the charge on the inner plates must equal the charge on the outer plates, raising questions about the mechanics of charge distribution.
  • Another participant notes that if the charges on plates a and b were unequal, it would result in excess charge leading to current flow in the connecting wire.
  • Concerns are raised about the complexities involved in inserting and removing dielectrics, particularly regarding the changes in voltage and charge distribution.
  • One participant references an assignment solution manual to illustrate how the dielectric affects the capacitor's behavior, indicating a need for clarity on the charge distribution when the dielectric is present.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and interpretation regarding the charge distribution and the effects of dielectrics. There is no consensus on the explanations provided, and multiple competing views remain regarding the underlying principles.

Contextual Notes

Some participants highlight the complexity of the problem, particularly in relation to charge distribution and the behavior of dielectrics, suggesting that there are unresolved aspects that require further exploration.

Who May Find This Useful

This discussion may be of interest to students and educators in physics or electrical engineering, particularly those studying capacitors, dielectrics, and electric charge behavior in circuits.

Nikitin
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Question 1:

Two condensers connected in series will be charged such that one gets +Q charge on one of its plates, and the other -Q.

Schematic: ------(-Q)| |(a)------(b)| |(+Q)-------

Can somebody prove (or at least show) intuitively to me why the plate "a" gets a +Q charge, and the plate "b" -Q?

Question 2:

A dialectic is inserted into a condenser made up of two plates. Afterwards, the condenser acts like it is two condensers connected in series. Why?
 
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Nikitin said:
Question 1:

Two condensers connected in series will be charged such that one gets +Q charge on one of its plates, and the other -Q.

Schematic: ------(-Q)| |(a)------(b)| |(+Q)-------

Can somebody prove (or at least show) intuitively to me why the plate "a" gets a +Q charge, and the plate "b" -Q?

Question 2:

A dialectic is inserted into a condenser made up of two plates. Afterwards, the condenser acts like it is two capacitors connected in series. Why?

The plates and wires initially ("uncharged") have + and - charges (electrons and the atoms they would "belong to at zero deg absolute")
These are all jostling together due to thermal agitation (300 deg above abs zero).
So at any INSTANT in any volume there IS a charge inbaleance + or -. This is called "Noise"
But LONG TERM average ther is none - it tends to disappear. "Flow away"
This is said to be "current flowing away"

When we apply a voltage, this pushes the charges aside, making one end of a wire or conductor + and the other -.
+ means there is a VERY SMALL % more + charges there then -ve. A charge migration.

Now look at your diagram how your capacitors are "connected in series"
The REASON a gets minus the charge b gets (equal and opposite) is a+b=0 total charge is all there is! We cannot CREATE charge - only move it around (ever so slightly)


Inserting dielectrics between plates and removing them is VERY TRICKY and misleading!
You DO WORK because of the force needed to remove the dielectric.
So the VOLTAGE changes
Also all surfaces have monofilms of WATER on them
The plates do: the dielectric does
So where does the charge (voltage: coulombs) REMAIN when the dielectric is removed!
 
You didn't understand my questions.

1) Why is a=-b=Q charged? Why is the charge of the two inner plates equal to the charge of the outer plates?

2) If a dialectic of length d is inserted between two parallel condenser-plates distanced D from each-other (d<D), the condensers act like they are connected in series. Why?
 
If the charge on a and b was smaller than Q, the two condensers would each have an excess charge and so they would pull/push electrons in the connecting wire. Only when the amount of positive and negative charge in each condenser is balanced will the external electric field vanish and only then will the current in the wire stop flowing.
Could you explain your second question in more detail? In which way does the capacitor act like two in series? If you put a dielectric inside the capacity increases.
 
Thanks for answering Q1.

As for Q2: That's how it is explained in the assignment. It's a weird problem. Look here at the solution-manual, assignment 4b ("Oppgave 4 b", page 4) http://folk.ntnu.no/sveinoll/ov/TFY/4155%20Elektrisitet%20og%20Elektromagnetisme/V11/LF/Ov06los.pdf .

The original situation is like A, and the condenser acts like in B.

Why would the dialectic suddenly be able to provide such a charge-distribution that it acts like a part of a condenser in series?
 
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Is nobody here smart enough to solve my professor's problem? Come on! :-p
 

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