Potential difference across a capacitor problem

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Homework Help Overview

The problem involves determining the potential difference across a capacitor in a circuit with multiple batteries and capacitors. The context centers on understanding the behavior of charge in a series circuit.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between current and charge in a series circuit, questioning the assumption that charges on the capacitors are equal despite differing capacitances.

Discussion Status

The discussion is exploring the reasoning behind charge equality in capacitors within a series circuit. Some participants have provided insights into current flow, while others are questioning the validity of the assumptions made regarding charge distribution.

Contextual Notes

There is an ongoing examination of the implications of having different capacitances in the circuit and how that affects the charge on the capacitors. The original poster's question highlights a potential gap in understanding the principles governing series circuits.

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Homework Statement



The problem is to find out the potential difference between P and Q in the following figure-

attachment.php?attachmentid=34660&stc=1&d=1303308181.jpg


The solution given takes the charges on two capacitors to be equal. Why is it so?
 

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It's a series circuit, so any current that flows while the circuit heads to equilibrium must be the same for all components. Same current --> same amount of charge moved.
 
Some amount of charge say Q1 may flow from the 22V battery to the 7V battery to charge the 2F capacitor. Q2 amount may flow from 7V battery to 22V battery. How can we say that the charges are equal unless the two capacitances are equal?
 
The current in a series circuit is everywhere the same. Any current that leaves the 22V battery's + terminal must also flow back into its - terminal. Same goes for the 7V battery, and all the other components in the series.
 
I got it now. Thanks!
 

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