Calculating Capacitance from Voltage-Time Data

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Homework Help Overview

The discussion revolves around calculating capacitance from voltage-time data in a lab setting. The original poster is attempting to derive capacitance using a linear relationship from an exponential decay equation related to capacitor discharge.

Discussion Character

  • Exploratory, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • The original poster outlines an equation relating voltage and time, seeking clarification on how to apply their measured data to calculate capacitance. They express uncertainty about using the time variable in their calculations. Other participants suggest plotting the data to identify a linear relationship and finding the slope as part of the process.

Discussion Status

The discussion is ongoing, with participants exploring the relationship between the measured voltage and time. Some guidance has been provided regarding the plotting of data, but there is no explicit consensus on the next steps or the correct interpretation of the time constant.

Contextual Notes

The original poster references an accepted value for capacitance, indicating a goal for their calculations. There is mention of potential confusion regarding the time constant and its application in the context of the problem.

jdog6
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This is for a lab I have done and I am stuck on this,

Question : Plot a curve of In (1 - V/Vo) vs time and calculate C from the slope of the line.

Initial equation = V = Vo(1-e^-t/RC)
Calculated Linear Equation : In (1 - V/Vo) = -t/RC
Therefore from y = mx + b = m = -t/RC (i think)
Then, C = -t/Rm

m = -72.673
R = 10 000 ohms
C = what we are looking for
-t = ? do i use any of my times

Also, C (accepted value) = 6000x10^-6 Farad
Therefore, answer should be near this.

Please help me out! I'm totally stumped. Thank you.
 
Last edited:
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Can anybody help?
 
i believe i have a lead t = time constant but i don't know what that is...
 
Yes you must plot all of your data. At each time, t, you measured some voltage, v,. Plot the points t, and

[tex]\ln ( 1 - \frac v v_0 )[/tex]

where v is your measured values. You should get something linear, find the slope of the line.
 

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