Engineering Find power of resistor and source in AC circuit

AI Thread Summary
The discussion focuses on calculating various parameters in an AC circuit with a 20Ω resistor dissipating 500W of power. The calculations yield Vrms as 100V, IS RMS as approximately 7.05A at an angle of 135 degrees, and a power factor of 0.707. The source voltage magnitude (VS) is determined to be 141.4V. The calculations are confirmed to be correct based on the provided equations and circuit analysis. Overall, the thread emphasizes the importance of understanding the relationships between voltage, current, and power in AC circuits.
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Homework Statement


If an average power of 500W is dissipated in the 20Ω resistor, find Vrms, I S RMS, the power factor seen by the source, and the magnitude of VS
(Based on circuit in attached diagram)

Homework Equations



Pave= Irms*Vrms*pf*\frac{1}{2}
Imaginary number referred to as "j", not "i".

The Attempt at a Solution


VA=V
By a node equation at node A, we see that \frac{V}{20}= \frac{V<sub>S</sub>}{-j*20}, so V = VS \angle-90

Loop 1: (j*20-j*20)IS -j*20I= VS
By observation, I=V/20, so V=VS\angle90.
Loop 2: (20+j*20)I-j*20IS=0, so IS= 1.41\angle135 *I
= 1.41\angle135 *\frac{V}{20}= 0.0705 V \angle135

Since I and V are in phase, the power across the resistor is 1
Solve for V:
500=V*\frac{V}{20}\frac{1}{2}, so V=\sqrt{20,000}=
100\sqrt{2}=141.4.

Vrms=\frac{V}{\sqrt{2}} =100,

Since V = 100\sqrt{2} IS =7.05 *\sqrt{2} \angle135, so I S RMS = 7.05

V=VS\angle90, so VS=V\angle-90
And IS= 0.0705 V \angle135,
So power factor pf = cos(135-90)= 0.707

VS=V\angle-90 = -141.4*j, so magnitude given by 141.4.

I think I got this right, but I just want to make sure.
 

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  • Circuit drawing.png
    Circuit drawing.png
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Physics news on Phys.org
Just realized the diagram I attached was small, hopefully this one's easier to read.
 

Attachments

  • Circuit drawing.jpg
    Circuit drawing.jpg
    21.4 KB · Views: 439
Same-same said:

Homework Statement


If an average power of 500W is dissipated in the 20Ω resistor, find Vrms, I S RMS, the power factor seen by the source, and the magnitude of VS
(Based on circuit in attached diagram)

Homework Equations



Pave= Irms*Vrms*pf*\frac{1}{2}
.
Bad start.
 

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