Electrical Engineering- Simple AC circuit problem

Click For Summary

Discussion Overview

The discussion revolves around a homework problem related to a series RL circuit connected to an AC source. Participants explore the relationship between the voltages across the resistor and inductor, specifically how to apply the phasor method and the relevant equations to find the voltage across the inductor.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant presents the problem and expresses confusion about the origin of the equation V_s^2 = V_r^2 + V_l^2.
  • Another participant explains that the impedance of an inductor is called inductive reactance and relates the problem to a right triangle where the hypotenuse is the total voltage (110 V) and one side is the voltage across the resistor (85 V).
  • A participant questions the characterization of the 110 V as the hypotenuse, suggesting that it may be in phase with the voltage across the resistor and that 85 V represents only the projection on the real axis.
  • A later reply indicates that the participant has resolved their confusion after reviewing the relevant section of their materials.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the voltage relationships in the circuit, particularly regarding the role of the 110 V as the hypotenuse and its phase relationship with the resistor voltage. The discussion remains unresolved on these points.

Contextual Notes

Participants reference the phasor method and the geometric interpretation of voltages in AC circuits, but there are unresolved assumptions regarding the phase relationships and the nature of the voltages involved.

Who May Find This Useful

Students learning about AC circuits, particularly those studying series RL circuits and the application of phasor methods in electrical engineering.

lubuntu
Messages
464
Reaction score
2

Homework Statement


I was able to find the solution to this problem but I don't understand where it comes from.

A series RL circuit is connect to a 110-V ac source. If the voltage across the resistor is 85 V, find voltage across inductor.



Homework Equations



Not sure.

The Attempt at a Solution



Solution is given as

V_s^2 = V_r^2 + V_l^2

then solve for V_l, I don't understand were that equation comes from or how it applies here. We are currently starting to learn how to solve circuits with the phasor method.
 
Physics news on Phys.org
The impedance of an inductor is called inductive reactance. It is called reactance to indicate that it is an imaginary number with no real part. (In reality all inductors have a small real part.) Because inductive reactance is at right angles to a resistor, the problem you are given amounts to a right triangle in which you are given the hypotenuse and one side. Now do you recognize the equation? The 110 VAC is the hypotenuse and the 85 VAC is the resistive voltage. Can you find the other side?
 
skeptic2 said:
The impedance of an inductor is called inductive reactance. It is called reactance to indicate that it is an imaginary number with no real part. (In reality all inductors have a small real part.) Because inductive reactance is at right angles to a resistor, the problem you are given amounts to a right triangle in which you are given the hypotenuse and one side. Now do you recognize the equation? The 110 VAC is the hypotenuse and the 85 VAC is the resistive voltage. Can you find the other side?

I understand they are at right angles to each other but I'm not sure why the hypotenuse is 110 V. Isn't the 110 V in phase with the V_r? so it points in the same direction as V_s? Isn't 85 V only the projects of the Voltage on the real axis and not the amplitude itself? What am I misunderstanding?
 
All set! For some reason the section that explained how that worked was the one after which this problem was presented.
 
Good
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 26 ·
Replies
26
Views
3K
  • · Replies 7 ·
Replies
7
Views
3K
Replies
0
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
Replies
15
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 19 ·
Replies
19
Views
5K