Capacitors connected in series?

  • Thread starter Thread starter mohamed el teir
  • Start date Start date
  • Tags Tags
    Capacitors Series
Click For Summary
When two capacitors are connected in series and then disconnected from a battery, they retain a charge Q on each plate. Reconnecting them in series without a voltage source will not result in a charge of 2Q on each capacitor, as the charges will equalize to zero due to the zero-sum nature of electric charge. If the capacitors are instead connected in parallel, the total charge can be calculated as 2Q, but this requires careful consideration of the voltage and resistance in the circuit. The discussion emphasizes that energy cannot be created from nothing; any additional charge must come from an external source, like a battery. Ultimately, the behavior of the capacitors depends on their configuration and the principles of charge conservation.
  • #31
re post #23 (Bottom left corner of the diagram)

The bottom capacitor goes from +Q, -Q to 0Q, +2Q. So the voltage polarity has reversed. That certainly looks like it's been discharged and recharged in the opposite direction :-)

A change from -Q to +2Q implies a current of 3Q flowed. Yet other nodes change from +Q to +2Q which is only an increase of Q. How is that possible if they are in series?
 
Physics news on Phys.org
  • #32
rumborak said:
Sorry, had not noticed the reversal of charges in case 3. But still, case 1 you can't really calculate like that. The formulas you are using presume ideal components; at the moment of your case 1 picture, you are short-circuiting ideal components. Meaning you have infinite current, and an unaccounted-for potential difference between the capacitors.
mmm, but i think all that in the paper doesn't hold unless c1 = c2, the final answers wouldn't change but the steps would change, for example in case 2 if c1 not equal c2 therefore Q1 will not be equal to Q2 but there summation still will be 2Q
 
  • #33
@CWatters, crap, you are correct, the picture is incorrect. The two right plates should read -2Q (top) and 0Q (bottom). Which would mean, when you cross them over, you are connecting a 2Q to -2Q. The reversal of polarity is what kills it in the end.

It was a nice idea, lol.

EDIT: Thinking about it more, there's also the argument that charges are a zero-sum game. If I create a 2Q somewhere, somewhere else must be -2Q. The only way of reconnecting it without massive discharge would be to find another 2Q potential. Which really could only come from another device.
Hmmmmm, got to think more about this.
 
Last edited:
  • #34
so i think case one would only be short circuit when c1=c2 :D , but if c1 not equal c2 so voltage will be distributed not equally between them (because in series) so i think it will not be shorted
 
  • #35
Throw a few diodes into the mix and you can make a high voltage charge pump..

http://en.wikipedia.org/wiki/Cockcroft–Walton_generator

220px-Cockcroft_Walton_voltage_multiplier_circuit.svg.png
 

Similar threads

  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 16 ·
Replies
16
Views
3K
Replies
7
Views
2K
  • · Replies 19 ·
Replies
19
Views
5K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 4 ·
Replies
4
Views
3K