Potential Difference and Resistors

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Homework Help Overview

The discussion revolves around a circuit problem involving three resistors with specified values and an emf of a battery. Participants are tasked with finding the potential difference across each resistor and the current flowing through them.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the application of Ohm's law and the loop and junction rules. There is confusion regarding the configuration of the resistors, with some suggesting that R2 and R3 are in series while R1 is in parallel with that combination. Questions arise about the concept of voltage in parallel versus series circuits.

Discussion Status

Some participants have offered guidance on how to approach the problem, including the relationships between voltage and current in different circuit configurations. There is an ongoing exploration of the concepts rather than a definitive resolution.

Contextual Notes

Participants express frustration with the problem and acknowledge mistakes in their calculations. There is a focus on understanding the underlying concepts rather than just obtaining the correct numerical answers.

ihearyourecho
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Homework Statement



Suppose the three resistors in the circuit have the values R1 = 180, R2 = 220, and R3 = 350, and that the emf of the battery is 18.0 V
http://session.masteringphysics.com/problemAsset/1126258/3/5416321031_128.jpg

Find the potential difference across each resistor.

Find the current that flows through each resistor.



Homework Equations



V=IR

The Attempt at a Solution



These things really confuse me, but here is my shot:
V=IR
Itotal=18/(1/180+1/220+1/350)=.233

I also know that due to the loop rule, the sum of all of the potential differences is 0. Because of the junction rule, the current flowing into a junction must equal what's flowing out. I'm just not sure how I can figure out either the V or I across a resistor if I have two unknowns...

any help would be awesome ! :)
 
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Itotal=18/(1/180+1/220+1/350)=.233
This is wrong.
R2 and R3 are in series and R1 is in parallel with that combination.
 
Oh, wow, that definitely was wrong. Stupid mistake because I'm frustrated with this stuff I guess. Itotal=136.8

The problem is more of I'm not sure what to do next though
 
18 V is common across R1 and (R2 +R3) combination.
So I1 = 18/R1
And I2 = 18/(R2+R3)
 
So Voltage is the same throughout all circuits? Or just in parallel circuits? I'm more looking for the concept of the whole thing more than the answer right now. Thanks for your help so far!
 
Also, when it wants V1,V2,V3 and I enter 18,18,18, that is not correct.
When it wants I1, I2, I3 (In mA) and I enter 100, 81.8, 51.4, that also is not correct.
 
ihearyourecho said:
So Voltage is the same throughout all circuits? Or just in parallel circuits? I'm more looking for the concept of the whole thing more than the answer right now. Thanks for your help so far!
In the parallel combination the voltage is common across each branch.
In each branch current may be different.
In a branch if there more than one resistance, then
V = V1+ V1 + ...
In the given problem
I1 = V/R1
I2 = V/(R2 + R3).
V2 = I2*R2
V3 = I2*R3
 
Oh, right on man. Thanks for your help! I'm pretty sure I understand now.
 

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