Find power of resistor and source in AC circuit

In summary, the conversation discusses finding Vrms, IS RMS, the power factor, and the magnitude of VS in a circuit where an average power of 500W is dissipated in a 20Ω resistor. The equations used include Pave= Irms*Vrms*pf*\frac{1}{2} and cos(135-90)= 0.707. The final values obtained are Vrms=100, IS RMS=7.05, pf=0.707, and VS magnitude=141.4. The attached diagram may be difficult to read.
  • #1
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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*[itex]\frac{1}{2}[/itex]
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 [itex]\frac{V}{20}[/itex]= [itex]\frac{VS}{-j*20}[/itex], so V = VS [itex]\angle[/itex]-90

Loop 1: (j*20-j*20)IS -j*20I= VS
By observation, I=V/20, so V=VS[itex]\angle[/itex]90.
Loop 2: (20+j*20)I-j*20IS=0, so IS= 1.41[itex]\angle[/itex]135 *I
= 1.41[itex]\angle[/itex]135 *[itex]\frac{V}{20}[/itex]= 0.0705 V [itex]\angle[/itex]135

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

Vrms=[itex]\frac{V}{\sqrt{2}}[/itex] =100,

Since V = 100[itex]\sqrt{2}[/itex] IS =7.05 *[itex]\sqrt{2}[/itex] [itex]\angle[/itex]135, so I S RMS = 7.05

V=VS[itex]\angle[/itex]90, so VS=V[itex]\angle[/itex]-90
And IS= 0.0705 V [itex]\angle[/itex]135,
So power factor pf = cos(135-90)= 0.707

VS=V[itex]\angle[/itex]-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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  • #2
Just realized the diagram I attached was small, hopefully this one's easier to read.
 

Attachments

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  • #3
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*[itex]\frac{1}{2}[/itex]
.
Bad start.
 

What is the purpose of finding the power of a resistor and source in an AC circuit?

The power of a resistor and source in an AC circuit is important because it tells us how much energy is being used or dissipated in the circuit. This information is crucial for understanding the efficiency and performance of the circuit.

How do you calculate the power of a resistor in an AC circuit?

The power of a resistor in an AC circuit can be calculated using the formula P = VI * cosθ, where V is the voltage, I is the current, and cosθ is the power factor. Alternatively, it can also be calculated using the formula P = I^2 * R, where R is the resistance of the resistor.

What factors affect the power of a source in an AC circuit?

The power of a source in an AC circuit can be affected by several factors including the voltage and current supplied by the source, the impedance of the circuit, and the power factor. The type and quality of the source also play a role in determining its power output.

Why is the power factor important in calculating the power of an AC circuit?

The power factor is important because it represents the efficiency of the circuit in converting electrical energy into usable work. A low power factor can result in wasted energy and higher electricity costs.

How can the power of a resistor and source be measured in an AC circuit?

The power of a resistor and source can be measured using a power meter, which measures the voltage and current and calculates the power using the aforementioned formulas. Other instruments such as oscilloscopes can also be used to measure the power in an AC circuit.

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