Linear circuit analysis question

Click For Summary

Discussion Overview

The discussion revolves around a homework problem related to linear circuit analysis, specifically focusing on replacing a resistor with a voltage source to ensure no power is absorbed by the resistors in the circuit. Participants explore the conditions under which power dissipation occurs in resistors and the implications of voltage sources in this context.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses uncertainty about how to start the problem, suggesting that the new voltage source might need to be 12V but feels this is too simple.
  • Another participant questions what the voltage across a resistor must be to avoid power dissipation, specifically asking about the voltage of a source at the resistor.
  • Several participants discuss the relationship between voltage and power dissipation, with one noting the formula P = V^2/R and questioning the meaning of "dissipating power."
  • There is a suggestion that power is zero when the voltage is zero, leading to a proposal that replacing the resistor with +12 volts would result in zero net voltage across the resistors.

Areas of Agreement / Disagreement

Participants generally agree that power dissipation is related to voltage across the resistors, and there is a consensus that power is zero when the voltage is zero. However, there is uncertainty regarding the specific voltage needed for the voltage source to achieve this condition, with differing opinions on whether +12 volts is appropriate.

Contextual Notes

There are unresolved assumptions regarding the circuit configuration and the specific conditions under which the voltage source is applied. The discussion does not clarify the exact relationship between the components involved.

Who May Find This Useful

This discussion may be useful for students studying circuit analysis, particularly those grappling with concepts of power dissipation and the application of voltage sources in circuits.

arkturus
Messages
27
Reaction score
0

Homework Statement



Replace resistor R with a voltage source such that no power is absorbed by either resistor; draw the circuit, indicating the voltage polarity of the new source.

circuit.jpg


Homework Equations



Ohm's law, Power = IV = I^2 * R

The Attempt at a Solution



I'm honestly not too sure how to begin the problem. The total voltage across the circuit should add up to zero, so I'm guessing the new voltage source must be 12V, but that seems too simple.

Thanks for the help.
 
Last edited:
Physics news on Phys.org
What must the voltage be across a resistor in order for that resistor not to dissipate power? What would the voltage of a voltage source at R be in order to achieve that condition?

E.g., start with the 15 k resistor at the top. What would the voltage have to be at the top of R in order for the 15k resistor not to dissipate power?
 
skeptic2 said:
What must the voltage be across a resistor in order for that resistor not to dissipate power? What would the voltage of a voltage source at R be in order to achieve that condition?

E.g., start with the 15 k resistor at the top. What would the voltage have to be at the top of R in order for the 15k resistor not to dissipate power?

I'm honestly not sure what the voltage must be through a resistor in order for it to not dissipate power. Is there a relationship I'm missing?
 
What is the formula for power dissipated by a resistor in terms of voltage?
 
skeptic2 said:
What is the formula for power dissipated by a resistor in terms of voltage?

Ah, got it. I was thinking in terms of P = I*V, but P = V^2/R works too.

I think my issue with the problem is the phrasing of "dissipating power". Does that mean that power will be zero?

I'm assuming the voltages would have to be 0 in order for power to be zero.
 
That's right, power is zero when the voltage is zero. What voltage would a voltage source at R have to be to get zero volts across the resistors?
 
skeptic2 said:
That's right, power is zero when the voltage is zero. What voltage would a voltage source at R have to be to get zero volts across the resistors?

Ah I got it, R should be replace with +12 volts. That way there is a net voltage of 0 throughout the circuit thus power at the top and bottom resistors must be 0?
 
Very good.
 
Thanks a lot, you were a big help
 

Similar threads

Replies
15
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 9 ·
Replies
9
Views
6K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 17 ·
Replies
17
Views
13K
  • · Replies 10 ·
Replies
10
Views
2K