Power dissipated in an RL circuit

AI Thread Summary
The discussion revolves around determining the two elements in an RL circuit with given voltage, current, and phase angle. The user initially miscalculated power using incorrect methods, including P=IR and rms values, leading to incorrect results. It was clarified that the power should be calculated using the real component of complex power, factoring in the power factor derived from the phase angle. The user recognized the need to include cos(36 degrees) in their calculations for accurate power dissipation. Ultimately, understanding the relationship between voltage, current, and phase angle is crucial for solving the problem correctly.
pengumon
Messages
4
Reaction score
0

Homework Statement



a) A circuit contains two elements, but it is not known if they are L, R or C. The current in this circuit when connected to a 2.16×102 V, 60.0 Hz source is 6.10 A and lags the voltage by 3.60×10^1 degrees. What are the two elements?

c) What is the power dissipated in this circuit?

Homework Equations



P=IV

The Attempt at a Solution



I determined that it was an LR circuit and calculated the impedance Z for part b) of the question but I'm stuck on the power. I did a simple P=IR to get an answer of 1.32E3 W but that was wrong, and I also tried dividing the I and V given by √2 to get rms values, then multiplying, which gave me 659 W but it's still wrong. Any insights or nudges in the right direction would be much appreciated!

Edit: I just realized my angle is 36 degrees, not 360 like I originally thought. That means I need to have a cos36 in there somewhere right? I'm still unsure as to whether I'm supposed to be using rms values or not though.
 
Physics news on Phys.org
pengumon said:

Homework Statement



a) A circuit contains two elements, but it is not known if they are L, R or C. The current in this circuit when connected to a 2.16×102 V, 60.0 Hz source is 6.10 A and lags the voltage by 3.60×10^1 degrees. What are the two elements?

c) What is the power dissipated in this circuit?

Homework Equations



P=IV

The Attempt at a Solution



I determined that it was an LR circuit and calculated the impedance Z for part b) of the question but I'm stuck on the power. I did a simple P=IR to get an answer of 1.32E3 W but that was wrong, and I also tried dividing the I and V given by √2 to get rms values, then multiplying, which gave me 659 W but it's still wrong. Any insights or nudges in the right direction would be much appreciated!

Edit: I just realized my angle is 36 degrees, not 360 like I originally thought. That means I need to have a cos36 in there somewhere right? I'm still unsure as to whether I'm supposed to be using rms values or not though.

You can assume that the voltage and current values given are RMS values unless otherwise indicated.

Note that the given current has a phase angle associated with it, which implies a power factor for the circuit. When they ask for power they want the real component of the complex power, which is the magnitude of the total power multiplied by the power factor.
 
I got it, thank you!
 
Thread 'Voltmeter readings for this circuit with switches'
TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
Thread 'Struggling to make relation between elastic force and height'
Hello guys this is what I tried so far. I used the UTS to calculate the force it needs when the rope tears. My idea was to make a relationship/ function that would give me the force depending on height. Yeah i couldnt find a way to solve it. I also thought about how I could use hooks law (how it was given to me in my script) with the thought of instead of having two part of a rope id have one singular rope from the middle to the top where I could find the difference in height. But the...
Back
Top