Voltage of Capacitors in Series, a widely held assumption

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Discussion Overview

The discussion centers around the voltage behavior of capacitors in series within a circuit, specifically questioning the widely held assumption that the voltages across individual capacitors add up to the total voltage supplied by the battery. Participants seek a proof based on electrostatics rather than Kirchhoff's Laws, exploring the underlying principles and seeking clarity on this concept.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the assumption that the voltages of capacitors in series add up to the total voltage, expressing dissatisfaction with existing explanations in physics texts.
  • Another participant references Maxwell's equations, suggesting that the integral form of the Maxwell-Faraday equation can lead to Kirchhoff's loop law, which states that the voltage in a loop sums to zero.
  • A participant expresses a desire for a more accessible explanation suitable for a Physics 2 student, indicating they are not yet comfortable with Maxwell's equations.
  • Another participant proposes using the concept of electric potential in electrostatics, explaining that the work done in a circuit depends only on the start and end points, leading to a total work done of zero in a closed loop.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the proof of the voltage relationship for capacitors in series. Multiple viewpoints and approaches are presented, indicating ongoing uncertainty and exploration of the topic.

Contextual Notes

There are limitations in the discussion, including the reliance on different levels of understanding of electrostatics and Maxwell's equations among participants, as well as the absence of a clear, universally accepted proof for the voltage addition in series capacitors.

Hirams_bro
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Say we have a simple circuit with just a battery and two capacitors. Why must the voltage of each capacitor in series add up to the total voltage of the battery? It seems intuitively plausible, I admit. But can someone show how to go about proving this using the laws of electrostatics ( please, not Kirchoff's Laws )?
I've already consulted 3 physics texts and none of them shed any light on this question. In one book, it says "clearly the voltage Vac = Vab + Vbc." That's it. Just because they wrote it in the form of an equation and said its clear, I guess they think they proved it. But that doesn't really prove much.
In Jewett's Physics for Scientists, their attempt at explaining this is to simply refer to a diagram and say "as can be seen, the diagram shows that these voltages add up..." Well drawing a diagram and labeling it doesn't it make it so. And this fact is used to prove the Law of Series Capacitance.

It seems to be a widely held assumption that individual voltages add up to the circuit voltage for series capacitors, but how can we assume this? I'm not aware of any conservation of voltage. Can someone please explain it?
 
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Thank you. I'm sure after this semester, when I finish Calc 3, I'll be able to make sense of Maxwell's Equations, gradient and curl, etc., and derive it from those. Until then is there any other way of showing this relationship, one that might be more familiar for a Physics 2 student?
 
OK, maybe try this. In electrostatics, we can use an electric potential instead of an electric field. Work done by a force usually depends on the path taken, but if the force can be represented by a potential, the work done only depends on the start and end points of the path. In a circuit, the charge starts out and ends up at the same place, so the total work done (charge times potential difference) in a loop is zero.
 

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