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The strange case of phase angles
ballsystemlord:
Hello,
I was doing some practice problems in my textbook and came upon a parallel RLC circuit. I calculated the phase angle using the impedance but my value differed from the answer key.
Puzzled, I tried obtaining it from the amperage and power vectors successfully. I tried reviewing my math, but can't figure out why my impedance vector doesn't yield the same result as the amperage and power ones. Which is correct? I thought I could try and build a circuit to test this, but the fact that this is a textbook circuit makes it unrealistic so I can't make one.
Attached are images of the problem, my calculator with results, and the answer key.
So, what's the correct phase angle? Why do the impedance and amperage/power vectors differ in their angles?
Thanks!
strawberry:
simulate in Qspice
ballsystemlord:
--- Quote from: strawberry on April 27, 2024, 08:44:45 am ---simulate in Qspice
--- End quote ---
Learning Qspice is in my next book. But I could wait.
EDIT: So far, I've done all calculations for all circuits by hand with a calculator, pen, and pencil.
Andy Watson:
The impedance of the capacitor should be combined with the impedance of the inductor in parallel; you appear to have combined them in series.
tooki:
And what that means is that to solve it trigonometrically, you can’t use the impedance (vector addition of resistance and reactance), but rather the admittance (vector addition of conductance and susceptance).
As an aside: as someone who sucks at trigonometry, I just use my calculator’s ability to work with polar complex numbers. So calculating IT, for example, I just type: 0.02 + 0.008∠-90 + 0.01571∠90 and get 0.02143∠21.1.
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