RC circuit with dc current source

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Discussion Overview

The discussion revolves around solving for the current in each branch of an RC circuit with a DC current source, focusing on the time dependence of the current and the voltage across the current source. The scope includes homework-related problem-solving and mathematical reasoning involving circuit analysis techniques.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant attempts to use the mesh method for circuit analysis but finds it confusing, particularly when substituting the capacitive impedance.
  • Another participant suggests using differential equations or Laplace transformations as potential methods for solving the problem.
  • A third participant clarifies that the second part of the question asks for the voltage across the current source as a function of time and mentions the need for initial conditions, such as assuming the capacitor voltage is zero at t=0.
  • A later reply expresses uncertainty about treating the current as varying with time and considers the possibility of needing to approach it like an AC circuit.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the second part of the question and the initial conditions needed for solving the circuit. There is no consensus on the approach to take, with differing opinions on whether to use differential equations or to treat the current as time-varying.

Contextual Notes

Participants note the lack of initial conditions provided in the problem statement, which may affect the ability to solve for the currents and voltages accurately. The discussion also highlights potential confusion regarding the interpretation of the problem's requirements.

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Homework Statement


Solve for the current in each branch of the following circuit as a function of time & derive and expression for the time dependence of the emf of the constant current source in the circuit below.


Homework Equations



Zc = Xc = 1/(wC) = t/(2pi*C)


The Attempt at a Solution



I attempted to use the mesh method:

Loop 1:
-1000(i1)+50-(Zc)(i1)+(Zc)(i2)=0

Loop 2
-(Zc)(i2)+(Zc)(i1)-3500(i2)+3500(i3)=0

Loop3:
-3500(i3)+3500(i2)-5000(i3)-V=0

This quickly got confusing when I substituted Zc for t/(2pi*120mF).
I have no idea how to solve this problem when it has both a capacitor and a current source.

I also do not understand what the second part of the question is asking.

I would appreciate any help/insight that you could offer. Thanks.
 

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We can't see your picture until it's been approved, but I can tell you that for these kind of questions, usually, you have to either use differential equations or Laplace transformations. I assume you're familiar with one of them?

The second part gets me too. I can understand each word separately, but put them together and it's jibberish to me. :blushing:
 
The 2nd part asks for the voltage across the current source, as a function of time.

As a start, you could get the steady-state currents and voltages (t→∞).

To solve this, I think we need some initial condition that isn't given. For example, perhaps the capacitor voltage is zero at t=0?
 
That's all the information that I'm given. I have a feeling that since the current varies with time that I have to treat it like an ac circuit, and put in a function instead of i. I'm meeting with my prof today, so hopefully he provides some more insight.
 

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