Help with circuits (Current, Voltage Drop, and Power Dissipation)

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Discussion Overview

The discussion revolves around calculating power dissipation, voltage drop, and current for three resistors connected to a 12V battery. Participants explore the application of relevant formulas and the implications of rounding in their calculations.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant states the formulas for voltage drop and power dissipation as Voltage Drop = Resistance * Current and Power Dissipation = V^2/R.
  • Another participant questions the application of V=IR in this context, suggesting that it may not apply.
  • One participant calculates voltage drops of 6V, 4V, and 2.5V for the resistors and a current of 0.05A, but later realizes that the total voltage drop exceeds the source voltage.
  • A participant calculates the total current using the total resistance and finds it to be approximately 0.048A, which they round to 0.05A.
  • Another participant suggests that rounding too early may have led to incorrect answers, and confirms that reentering values without rounding yielded correct results.

Areas of Agreement / Disagreement

Participants express differing views on the application of formulas and the impact of rounding on their calculations. There is no consensus on the correct approach to the problem, as some participants arrive at different values for current and voltage drop.

Contextual Notes

Participants' calculations depend on their interpretations of the circuit configuration and the application of Ohm's law. There are unresolved mathematical steps regarding the total resistance and how it affects the current and voltage drops across individual resistors.

sloan13
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Homework Statement



Basically, I need to know the power dissipation (W) for three resistors using aw 12V battery: 120, 80, and 50 ohms.

https://webwork2.uncc.edu/webwork2_files/tmp/Fall2014-Engr1201-Common/img/2ff2f0ce-cb10-3786-8109-c42346130316___1a2e5eeb-8657-3983-941f-b7d8a9123afa.gif

Homework Equations


I think the formula for voltage drop is Voltage Drop = Resistance * Current, and I thought the formula for power dissipation was V^2/R.

The Attempt at a Solution



It also asks for the current, which I think is 0.05A and voltage drop across all three resistors.

I think the answers for voltage drop are 6, 4, and 2.5 V, and the current was 0.05A.

I thought the power dissipation for the three resistors were 1.2, 1.8, and 2.9 W.

The website says I got "at least one wrong." Thanks, WeBWork.
 
Last edited by a moderator:
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I just got the power dissipation problems. All I need is the voltage drop. Apparently, V=IR doesn't apply here?
 
sloan13 said:

Homework Statement



Basically, I need to know the power dissipation (W) for three resistors using aw 12V battery: 120, 80, and 50 ohms.

https://webwork2.uncc.edu/webwork2_files/tmp/Fall2014-Engr1201-Common/img/2ff2f0ce-cb10-3786-8109-c42346130316___1a2e5eeb-8657-3983-941f-b7d8a9123afa.gif

Homework Equations


I think the formula for voltage drop is Voltage Drop = Resistance * Current, and I thought the formula for power dissipation was V^2/R.


The Attempt at a Solution



It also asks for the current, which I think is 0.05A and voltage drop across all three resistors.

I think the answers for voltage drop are 6, 4, and 2.5 V, and the current was 0.05A.

I thought the power dissipation for the three resistors were 1.2, 1.8, and 2.9 W.

The website says I got "at least one wrong." Thanks, WeBWork.

Adding your voltage drops gives 12.5V, which is more than your voltage source.

I also got a different current when I divided 12V/Rtotal. Can you show your work in those two steps?
 
Last edited by a moderator:
berkeman said:
Adding your voltage drops gives 12.5V, which is more than your voltage source.

I also got a different current when I divided 12V/Rtotal. Can you show your work in those two steps?

12V/250(Rtotal) = 0.048A which I rounded to 0.05A.

Vdrop1 = 120 * .05 = 6
Vdrop2 = 80 * .05 = 4
Vdrop3 = 50* .05 = 2.5

Do you think I just rounded too early?
 
Yea, I reentered them without rounding, and they were correct. Thank you, berkeman.
 
sloan13 said:
Yea, I reentered them without rounding, and they were correct. Thank you, berkeman.

Glad to help. Yeah, definitely don't round anything until the end. :smile:
 

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