RC time constant problem — confusing problem statement

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Discussion Overview

The discussion revolves around a problem related to the time constant of an RC circuit, specifically focusing on calculating the energy remaining in the circuit after a specified time. The problem lacks clarity regarding whether the scenario involves a charging or discharging capacitor.

Discussion Character

  • Homework-related, Technical explanation

Main Points Raised

  • One participant notes the ambiguity in the problem statement regarding the direction of the voltage change (charging or discharging).
  • Another participant suggests interpreting "remaining" energy as the energy in a discharging scenario, proposing to calculate the remaining energy as a fraction of the initial energy based on the initial voltage.
  • A third participant shares their solution approach, indicating they followed the advice given and found it reasonable.
  • A subsequent reply acknowledges the solution shared but comments on the readability of the provided photo.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the interpretation of the problem statement, as the ambiguity regarding the charging or discharging scenario remains unresolved.

Contextual Notes

The discussion highlights the lack of specific details such as initial voltage and capacitance, which are necessary for a complete solution.

Abo
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Homework Statement
It says that the Time Constant of an RC circuit is equal to 100 ms. What is the energy that remains in the circuit after 300 ms? "Nothing mentioned about whether it is in falling or rising edge".
Relevant Equations
The formulas that I have been using are :
W = 0,5 (C* V^2)
V = V0 ( e^-t/rc )
Hello!
It says that the Time Constant of an RC circuit is equal to 100 ms. What is the energy that remains in the circuit after 300 ms? "Nothing mentioned about whether it is in falling or rising edge".
The formulas that I have been using are :
W = 0,5 (C* V^2)
V = V0 ( e^-t/rc )
since I don't have the details about neither the initial voltage nor the capacitance I really don't know how to compute the energy? would it be a numerical value?
 
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Welcome to the PF.

If that's all the problem states, then I would take the word "remaining" to mean that the capacitor is being discharged by the resistor. And assume the initial energy stored is Eo based on an initial capacitor voltage of Vo. Then calculate the energy after 300ms as a fraction of Eo.

Give that a try and see how it goes... :smile:
 
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Thank you for your reply. I did as you told me and I think it seems reasonable. Here is a photo of the solution.
241815
 
The photo is a little hard to read, but it looks good to me. Good work! :smile:
 
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Likes   Reactions: Abo

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