Engineering Solving phasor circuit with unknown dep. current src

AI Thread Summary
The discussion revolves around solving a phasor circuit with an unknown dependent current source. The initial approach involves combining a capacitor and a 2-ohm resistor in parallel, resulting in an impedance of Z = 1-j. However, complications arise when adding the inductor's impedance without considering the current through the capacitor. The correct voltage across the combined elements is crucial for determining the current through the circuit, which ultimately affects the calculation of the imaginary part of the impedance. The final consensus is that a more careful analysis of the combined impedance and current flow is necessary to arrive at the correct solution.
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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