Should Vout be negative or positive?

  • Thread starter Thread starter Clandry
  • Start date Start date
  • Tags Tags
    Negative Positive
Click For Summary

Homework Help Overview

The discussion revolves around a circuit analysis problem involving Kirchhoff's voltage law and the determination of the output voltage (V_out). Participants are examining the signs of voltage in relation to circuit components and their configurations.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the application of Kirchhoff's voltage law and the implications of current direction on voltage calculations. There are inquiries about the polarity of V_out and whether it can be determined without solving the entire problem.

Discussion Status

Some participants have provided affirmations regarding the sign of V_out, while others have suggested methods for visualizing voltage differences in the circuit. The conversation includes reflections on prior experience with similar problems, indicating a mix of perspectives on understanding voltage polarity.

Contextual Notes

There is mention of voltage sources and their relative potentials, as well as the importance of drawing voltage and current arrows for clarity in circuit analysis. The discussion hints at the complexity of interpreting circuit behavior without complete information.

Clandry
Messages
74
Reaction score
0
I attached the circuit.

I did kirkoff's voltage law (assuming current goes clockwise):
-15+5-10,000I-40000I=0 where I=current
I=-2*10^-4 A

V_out=40,000*-2*10^-4A = -8V
The way V_out is shown, it should solve to be negative, correct?
 

Attachments

  • Untitled.png
    Untitled.png
    4.3 KB · Views: 772
Physics news on Phys.org
Clandry said:
The way V_out is shown, it should solve to be negative, correct?

Correct.
 
V is the difference between potentials at two places in the circuit.
If you look at the voltage sources, the top is less positive than the bottom - so the bottom must have a higher potential than the top. Replace the voltage sources with an equivalent single voltage source and the answer to your question will become clear.

Note: when you do kirkoffs laws to analyze a circuit - draw voltage arrows on the components as well as current arrows at the nodes.
 
gneill said:
Correct.
Did you solve the problem?
I'm asking because if you didn't, can you tell just by looking it that it will be negative?
 
Clandry said:
Did you solve the problem?
I'm asking because if you didn't, can you tell just by looking it that it will be negative?

Yes, I can tell just by looking; But I've looked at a LOT of circuit problems over the years!

I took note of the two voltage supplies and determined that the top of them will be negative w.r.t. the bottom. I then looked at the polarity specified for "measuring" the output and drew the conclusion that Vout must be negative.
 

Similar threads

When is the acceleration due to gravity negative and when is it positive?
  • · Replies 13 ·
Replies
13
Views
6K
Undergrad Checking for negative feedback in a circuit
  • · Replies 3 ·
Replies
3
Views
1K
Work done in elevator problem — is it positive or negative?
  • · Replies 3 ·
Replies
3
Views
3K
How does the negative feedback amplifier below work?
  • · Replies 7 ·
Replies
7
Views
2K
Understanding Loop Currents: Why is I3 Negative?
  • · Replies 1 ·
Replies
1
Views
1K
How do I fix the signs in Faraday's Law in RL Circuit?
  • · Replies 5 ·
Replies
5
Views
1K
Single Loop Potential difference -- sign issue
  • · Replies 8 ·
Replies
8
Views
2K
Maximum charge on the plates of a capacitor
  • · Replies 2 ·
Replies
2
Views
2K
Determine the Thevenin equivalent circuit
  • · Replies 2 ·
Replies
2
Views
2K
How to obtain correct negative sign in calculation of motional emf?
  • · Replies 2 ·
Replies
2
Views
1K