Calculating Capacitor Variance/Uncertainty

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Discussion Overview

The discussion revolves around calculating the uncertainty in charge (Q) for capacitors in series and parallel circuits, given uncertainties in capacitance and voltage. Participants explore methods to derive these uncertainties based on provided values and equations.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant seeks guidance on calculating charge uncertainty given capacitance and voltage uncertainties in a simple circuit setup.
  • Another participant requests clarification on what is meant by "charge uncertainty."
  • A participant provides additional context by linking to a more detailed question, specifying the uncertainties in capacitance (5%) and voltage (1%), and mentions an equation for calculating uncertainty.
  • Another participant suggests that the uncertainty in charge can be derived from the nominal values of capacitance and voltage, proposing a method to calculate minimum and maximum values to determine the uncertainty range.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the method for calculating total charge uncertainty, and multiple approaches are being discussed without resolution.

Contextual Notes

Participants have not fully defined the assumptions behind their calculations, and there may be dependencies on specific definitions of charge uncertainty that remain unclear.

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I can't seem to find out how to calculate a charge's uncertainty when given capacitance & voltage across a series & parallel circuit. Simple circuit setup w/voltage and the 2 capacitors.

Any suggestions?Thanks!
 
Last edited:
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Hi Blog,

Could you give somemore details - and what you mean by 'charge uncertainty'?

Thanks

Tom
 
Hey Tom,

I had to adjust the question, because it was formatted as a "homework question" so I posted the entire question here: https://www.physicsforums.com/showthread.php?t=126165

Basically, I'm given Capacitance uncertainty(5%) & Voltage uncertainty(1%), as well as the Capacitance & voltage across a simple DC circuit(one Series & one Parallel circuit).

The question was a 2 part, find Q(charge) as well as its uncertainty based on the information above.I finally came across this equation:

(Delta.Z / Avg.Z) = sqrt( (delta.X/avg X)^2 + (delta.Y/avg.Y)^2 )

I was able to find each capacitor's charge uncertainty, except for Q.total's Charge Uncertainty, when using C.eqThanks.
 
Hmmm... well, we know c=q/v, so q=cv (obviously not straight out of the problem, but you can calculate the nominal values). I would guess the uncertainty is just the range of uncertainties possible for c and q after that. So you know the nominal value easily, and you can calculate the minimum and maximum values, giving you your uncertainty range
 

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