What is the value of R3 in the circuit given?

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Homework Help Overview

The discussion revolves around a circuit analysis problem involving resistors R1, R2, R3, and R4, with given values for resistances and currents. The original poster expresses confusion about the role of R3, particularly its diagonal representation in the circuit diagram and its relationship to R2 and R4.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to understand the configuration of R3 in relation to R2 and R4, questioning whether they are in series or parallel. Some participants suggest labeling the diagram and using known values to clarify the circuit. Others propose visualizing R3 differently to aid understanding.

Discussion Status

Participants are actively engaging with the problem, offering guidance on how to approach the circuit analysis. There is a recognition of the need to determine the current through R3 and the voltage across it, with some participants providing specific calculations and insights. However, there is no explicit consensus on the interpretation of R3's role yet.

Contextual Notes

The original poster mentions a lack of reference materials, which may contribute to their confusion regarding circuit analysis concepts. There is also a mention of a specific answer for R3 being 20 ohms, but the reasoning behind this is still being explored.

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Homework Statement



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In the circuit shown, R1 = 1 ohms, R2 = 10 ohms, I1 = 3.5 A and I4 = 2 A. The battery has negligible internal resistance. If the rate at which R4 is dissipating electrical energy is 20W:

a) What is R4
b) What is R3
c) What is I3
d) What is the emf of the battery?

Homework Equations


The Attempt at a Solution



I solved for a:
P = (I4)R R4
20 W = 4 R4
R4 = 5 ohms.

Now I am stuck there. Honestly, I don't know what the R3 illustration means. I know that R2 and R4 are parallel to each other. But the R3 which is like a diagonal confuses me. What does that R3 mean? And how do I go about to solve this?

Does the R3 mean that it connects the R2 and R4, which makes them in series? I am reallly confused and I don't have a book to consult this to.
 
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Don't let diagonal lines fool you; Connections are connections no matter how the lines are drawn on paper.
 
I still don't get it. The answer to R3 should be 20 ohms. But I can't think of any solution that will lead to that.
 
Start by labeling your diagram with everything you know or can determine so far. That would include indicating given currents and component values, as well as any voltage drops you can determine from the given resistances and currents. Find the current that must be flowing through R3 and the voltage that must be across it.
 
If it helps to imagine that R3 is straight up and down then do so, the resistors R2, R3, and R4 are all in parallel and no matter how it is drawn the laws governing them remain the same.
 
I really can't understand this.. I tried this:

If R3 is parallel to R2.

R23 = R2R3 / R2+R3 = 10R3 / 10+R3
I23 = I2 + I3 = 1 + I3
V23 = V2 = 10V = V3

Is that right? What should I do next?
 
Did you label your diagram with all the currents you know? Can KCL help you to find I3?
 
Oh in that case, I found I3 to be 0.5A.

Thus, R3 = V3 / I3
R3 = 10 / 0.5 = 20 ohms

Thanks!
 

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