Why Don't We Invert the Signs of Voltage in Circuit Analysis?

  • Thread starter Thread starter Ammar w
  • Start date Start date
  • Tags Tags
    Sources
Click For Summary
SUMMARY

The discussion centers on the importance of maintaining consistent voltage polarity in circuit analysis, specifically regarding the voltage VA across a 15Ω resistor. It highlights that the current must flow from the positive to the negative terminal of the resistor, which dictates how voltage is measured. The conversation also emphasizes that if the signs of VA are inverted, the polarity of the controlled voltage source 2VA must also be reversed to maintain the integrity of the Kirchhoff's Voltage Law (KvL) equation. The KvL equation transitions from -120 + V30 + 2VA - VA = 0 to -120 + V30 - 2VA + VA = 0 when the signs are flipped.

PREREQUISITES
  • Understanding of Kirchhoff's Voltage Law (KvL)
  • Basic knowledge of circuit components, specifically resistors and voltage sources
  • Familiarity with voltage measurement techniques using voltmeters
  • Concept of polarity in electrical circuits
NEXT STEPS
  • Study the principles of Kirchhoff's Voltage Law in detail
  • Learn about the behavior of controlled voltage sources in circuit analysis
  • Explore voltage measurement techniques and their impact on circuit analysis
  • Investigate the effects of polarity changes on circuit equations
USEFUL FOR

Electrical engineering students, circuit designers, and anyone involved in circuit analysis and design who seeks to understand the implications of voltage polarity in their work.

Ammar w
Messages
28
Reaction score
0

Homework Statement



https://www.diigo.com/item/image/2sb3i/1svo

Why don't we flip the signs of VA like this :

https://www.diigo.com/item/image/2sb3i/g2a4

because the current must flow from + to - of the resistor.

Homework Equations


none


The Attempt at a Solution


none
 
Last edited by a moderator:
Physics news on Phys.org
The "+ -" tags on the 15Ω resistor tell you which way to "measure" the potential VA; It's like specifying how to orient the positive and negative leads of a voltmeter on the component.

You could change the tags as you suggest IF you also reverse the polarity of the controlled voltage source 2VA, since its output depends on how VA is "measured".
 
thanks
and the KvL equation changes from :
-120+V30+2VA-VA = 0

to :
-120+V30-2VA+VA = 0
 

Similar threads

KVL Exercise: Basic Homework Statement & Solution
  • · Replies 8 ·
Replies
8
Views
2K
Engineering Why is the voltage source high potential into node 1 at -12 V in this op amp problem?
  • · Replies 15 ·
Replies
15
Views
2K
Engineering How do I find Vth with the node voltage method?
  • · Replies 10 ·
Replies
10
Views
4K
Engineering Circuit with multiple voltage sources
  • · Replies 11 ·
Replies
11
Views
5K
Engineering Basic circuit problem -- Resistor network and a voltage source
  • · Replies 6 ·
Replies
6
Views
2K
Engineering Why is the output voltage of the subtractor calculated like this?
  • · Replies 5 ·
Replies
5
Views
2K
What is the Result of \(\vec{A} - \vec{B}\) Given Three Vectors Summing to Zero?
  • · Replies 4 ·
Replies
4
Views
5K
The validity of the interconnection of ideal sources
  • · Replies 16 ·
Replies
16
Views
6K
Engineering How to deal with dc source on ac circuits?
  • · Replies 7 ·
Replies
7
Views
3K
Engineering Why Is Nodal Analysis Confusing in This Circuit Example?
  • · Replies 7 ·
Replies
7
Views
2K