Electricity - Solving unknown variables for mixed circuits

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Discussion Overview

The discussion revolves around solving for unknown variables in a mixed circuit involving resistors and voltage sources. Participants are analyzing a homework problem that requires the application of Kirchhoff's law and Ohm's law to determine voltages and currents in the circuit.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant presents an attempt at a solution, calculating various voltages and currents based on their understanding of the circuit configuration.
  • Another participant challenges the initial calculations, stating that the first equation is incorrect and suggesting that an equivalent resistance should be found first.
  • A follow-up question is posed regarding the reasoning behind not being able to add R1 and R3, with a participant seeking clarification on their series connection.
  • Another participant clarifies that R1 and R2 are in parallel, indicating that they cannot be added directly as proposed in the initial solution.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there are competing views on the correct approach to solving the circuit problem. Disagreement exists regarding the configuration of the resistors and the method of calculating equivalent resistance.

Contextual Notes

There are unresolved assumptions regarding the circuit layout and the definitions of series and parallel connections, which may affect the calculations presented.

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Homework Statement


7. Find V1, V2, V3, I0, I1, I2, and I3 for the circuit in Figure 2.

photo.JPG


V0 = 120V
R3=15 ohms
R1=3 ohms
R2 = 6 ohms

Homework Equations


Kirchoff's law
Ohm's law

The Attempt at a Solution

R0 = R1 + R3
= 3 + 15
=18 ohms I0=V0/R0
=120/128
=6.66A

I1=I3=I0
I1=I3=6.66AV3=R0 X I3
= 18 X 6.66
=99.9V

V1=V0 - V3
=120-99.9
=20.1V

V2=V1
V1=20.1V
I2 = V2/R2
= 20.1/6
=3.35A

This is what I did but when I look at the back of the textbook it gives me different answers.
 
Last edited:
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First equation is wrong. You can't add those two resistors.

Find an equivalent resistance first.
 
SirAskalot said:
First equation is wrong. You can't add those two resistors.

Find an equivalent resistance first.

How come you can't add R1 and R3? Aren't they both in a series circuit?
 
You can't add them because they are in different loops. R1 and R2 are in parallel, so start from there.
 

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