How to find power dissipation in combination circuit?

Click For Summary

Homework Help Overview

The discussion revolves around calculating the power dissipation in a 34-Ohm resistor within a combination circuit involving both series and parallel resistors. The original poster seeks clarification on the correct approach to determine the voltage across the resistor and subsequently the power dissipated.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the total current in the circuit and the voltage across the resistors. There are attempts to clarify the configuration of the resistors (series vs. parallel) and how this affects the calculations for power dissipation.

Discussion Status

Some guidance has been provided regarding the voltage across parallel resistors and the need to identify the correct configuration of the circuit. Participants are exploring different interpretations of the circuit layout and how it impacts their calculations.

Contextual Notes

There is uncertainty regarding the voltage across the 34-Ohm resistor and how to accurately apply the power formula given the circuit's configuration. Participants are also navigating the implications of combining resistors in series and parallel.

boilerpilot
Messages
8
Reaction score
0

Homework Statement



What is the power dissipated in the 34-Ohm resistor?

SCAN0007.jpg


Homework Equations



P=RI^2

The Attempt at a Solution



I have found the total current in the system as well as the current through the resistor, and keep getting 1.88, which is incorrect. Any suggestions on where I am going wrong?
 
Physics news on Phys.org
Nobody can find your mistake without seeing your work.

ehild
 
Ok, I guess I need to clarify my work. Here is what I have so far...

Rtotal=35.88
I=8/35.88=.222965
P=E2/R
P=82/34
P=1.8823W

The part that confuses me is the combination circuit part, and I am not sure how that plays into the power dissipation of the resistor...
 
The voltage is not 8 V across the 34 ohm resistor. Try to find it out.
The parallel resistors can be replaced by their resultant, and this is in series with the 25 ohm resistor. You know the current flowing both series resistors. What is the voltage across the resultant of the parallel ones?

ehild
 
ehild said:
The voltage is not 8 V across the 34 ohm resistor. Try to find it out.
The parallel resistors can be replaced by their resultant, and this is in series with the 25 ohm resistor. You know the current flowing both series resistors. What is the voltage across the resultant of the parallel ones?

ehild

I don't really know what you mean. Isn't voltage equal across a parallel circuit? I also don't know what you mean by two series resistors...Is this circuit a series (with the 16 and 25 Ohm) with a parallel circuit (34 Ohm)? Or a parallel (16 and 34) with one in series (25 Ohm)? I have tried to solve this either way, but I can't figure out how much power is dissipated in that 34 Ohm resistor.
 
boilerpilot said:
I don't really know what you mean. Isn't voltage equal across a parallel circuit? I also don't know what you mean by two series resistors...Is this circuit a series (with the 16 and 25 Ohm) with a parallel circuit (34 Ohm)? Or a parallel (16 and 34) with one in series (25 Ohm)? I have tried to solve this either way, but I can't figure out how much power is dissipated in that 34 Ohm resistor.

I'd just combine all the resistors (I think you did this at one point), to find out what the current is through the circuit. All that current goes through the bottom resistor, so you can calculate the voltage across that resistor. The rest of the voltage is across the parallel combination of resistors to the left, and there's an equation for power dissipated in a resistor when it has a voltage across it...
 
berkeman said:
I'd just combine all the resistors (I think you did this at one point), to find out what the current is through the circuit. All that current goes through the bottom resistor, so you can calculate the voltage across that resistor. The rest of the voltage is across the parallel combination of resistors to the left, and there's an equation for power dissipated in a resistor when it has a voltage across it...

The current through the 25 Ohm resistor is .222965A. This means the voltage across the resistor is 5.574V. This leaves 2.426V unaccounted for. How do I know how much power is dissipated from the rightmost resistor?
 
boilerpilot said:
The current through the 25 Ohm resistor is .222965A. This means the voltage across the resistor is 5.574V. This leaves 2.426V unaccounted for. How do I know how much power is dissipated from the rightmost resistor?

That leftover voltage is across both of the right-hand resistors. What's the equation for the power dissipated in a resistor based on the voltage across it and the resistance? You can use that same formula to calculate the power dissipated across each of the right side resistors individually.
 
berkeman said:
That leftover voltage is across both of the right-hand resistors. What's the equation for the power dissipated in a resistor based on the voltage across it and the resistance? You can use that same formula to calculate the power dissipated across each of the right side resistors individually.

P=RI2=V2/R

Assuming this is the correct equation, I know R (34 Ohms) but that's it, right? I don't know current or voltage (the only voltage I know is what's left over). How can I separate that to find what I need for the 34 Ohm resistor?
 
  • #10
boilerpilot said:
I don't really know what you mean. Isn't voltage equal across a parallel circuit? I also don't know what you mean by two series resistors...Is this circuit a series (with the 16 and 25 Ohm) with a parallel circuit (34 Ohm)? Or a parallel (16 and 34) with one in series (25 Ohm)? I have tried to solve this either way, but I can't figure out how much power is dissipated in that 34 Ohm resistor.

The voltage is equal across parallel connected resistors. How do you know if two resistors are connected in parallel? Which ones in this circuit are connected in parallel?

ehild
 
  • #11
ehild said:
The voltage is equal across parallel connected resistors. How do you know if two resistors are connected in parallel? Which ones in this circuit are connected in parallel?

ehild

It looks to me like the 16 Ohm and 34 Ohm resistors are in parallel. Is that correct? Does this mean that the 16 Ohm and 34 Ohm resistors each have 2.426V across them?
 
  • #12
boilerpilot said:
It looks to me like the 16 Ohm and 34 Ohm resistors are in parallel. Is that correct? Does this mean that the 16 Ohm and 34 Ohm resistors each have 2.426V across them?

Yes.
 
  • #13
berkeman said:
Yes.

So...for the win...

P=V2/R
P=2.4262/34
P=.1731W

Is this correct?
 
  • #14
Yes.

ehild
 
  • #15
ehild said:
Yes.

ehild

Thanks ehild and berkeman for all the help. I sincerely appreciate it.
 

Similar threads

Power dissipated in this circuit with 2 batteries and 3 resistors
  • · Replies 22 ·
Replies
22
Views
4K
Graphing the Power dissipated in a resistor
  • · Replies 1 ·
Replies
1
Views
2K
Power Resistor Immersed In Water
  • · Replies 4 ·
Replies
4
Views
3K
What happens to the total power dissipated in the circuit ?
  • · Replies 13 ·
Replies
13
Views
4K
What is the Mistake in Calculating Power Dissipation in a Resistor?
  • · Replies 10 ·
Replies
10
Views
3K
Power Dissipated By Resistor is LRC Circuit
  • · Replies 3 ·
Replies
3
Views
4K
What Is the EMF of a Cell with Given Energy Dissipation and Current?
  • · Replies 4 ·
Replies
4
Views
5K
How Does Power Dissipation in One Resistor Relate to Total Power from Batteries?
  • · Replies 1 ·
Replies
1
Views
2K
How Much Energy is Dissipated in a Resistor in 0.75 Seconds?
  • · Replies 3 ·
Replies
3
Views
3K
Power dissipated by a resistor in parallel
  • · Replies 6 ·
Replies
6
Views
8K