Solving phasor circuit with unknown dep. current src

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Discussion Overview

The discussion revolves around solving a phasor circuit that includes an unknown dependent current source, focusing on the application of circuit analysis techniques involving impedances of capacitors, resistors, and inductors. Participants are attempting to simplify the circuit and calculate voltages and currents across various components.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant simplifies the circuit by combining a capacitor and a 2-ohm resistor in parallel, calculating an impedance of Z = 1 - j and then adding the inductor's impedance.
  • Another participant suggests that while combining the capacitor and resistor is a good start, adding the inductor's impedance at that point may not be appropriate, emphasizing the need to consider the current through the capacitor.
  • A participant mentions knowing the voltage across the combined elements and calculates the current through them by dividing by their combined impedance.
  • There is a reference to a "black box" representing the combined impedance of the capacitor and resistor, which is then combined with the inductor to find the voltage across the current source and the 5-ohm resistor.
  • One participant expresses uncertainty about the imaginary part of their calculations, indicating a discrepancy between their result and the expected answer.

Areas of Agreement / Disagreement

Participants express differing views on the correct approach to adding the inductor's impedance and the implications for calculating currents and voltages. There is no consensus on the correct method or final answers, as participants are refining their understanding and calculations.

Contextual Notes

Participants are working through assumptions related to the circuit configuration and the relationships between voltages and currents in the context of phasor analysis. Some steps in the calculations remain unresolved or unclear.

Who May Find This Useful

This discussion may be useful for students and practitioners interested in phasor circuit analysis, particularly those grappling with the complexities of combining impedances and understanding the behavior of dependent sources in AC circuits.

x86
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Homework Statement


Selection_029.png


Homework Equations


V=IR

The Attempt at a Solution


I try to simplify the circuit by combining the capacitor and 2ohm resistor in parallel, Z = 1-j. Then I add the inductor to get Z = 1. Knowing the current across the resistor, 2(0d) I find the voltage across the 5 ohm resistor (2(0d)). So 2/5(0d).

The real part is 0.4 (correct). The imaginary part is 0 (incorrect)??

The answer for the imaginary part is 0.4 But I don't get this in my attempt.
 
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x86 said:
I try to simplify the circuit by combining the capacitor and 2ohm resistor in parallel, Z = 1-j. Then I add the inductor to get Z = 1. Knowing the current across the resistor, 2(0d) I find the voltage across the 5 ohm resistor (2(0d)). So 2/5(0d).
Combining the capacitor and 2 Ohm resistor is a good start. But then adding the inductor's impedance to it at that point is not so good.

You see, you may know the current through the resistor thanks to having its potential difference, but there is also the current through the capacitor to consider. What must the current be through the combined impedance (cap || resistor) in order for the potential difference across it to end up being 4V @ 0°?
 
gneill said:
Combining the capacitor and 2 Ohm resistor is a good start. But then adding the inductor's impedance to it at that point is not so good.

You see, you may know the current through the resistor thanks to having its potential difference, but there is also the current through the capacitor to consider. What must the current be through the combined impedance (cap || resistor) in order for the potential difference across it to end up being 4V @ 0°?

If I'm not misaken, after combining the resistor and capacitor, I know the voltage through them both is V1. Then by dividing by their combined impedence, I get the current through these two elements, which I draw a black box.

So now I know the current through this black box. I combine the impedence of the black box and inductor, multiplying by the current, to get the voltage. Now I know the voltage across the current source and the 5 ohm resistor (they are in parallel).
 
x86 said:
If I'm not misaken, after combining the resistor and capacitor, I know the voltage through them both is V1. Then by dividing by their combined impedence, I get the current through these two elements, which I draw a black box.

So now I know the current through this black box. I combine the impedence of the black box and inductor, multiplying by the current, to get the voltage. Now I know the voltage across the current source and the 5 ohm resistor (they are in parallel).
Yes, that would work fine.
 

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