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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.