Simple circuit analysis w/ voltage sources - MasteringPhysics wrong?

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SUMMARY

The forum discussion centers on a circuit analysis problem involving four resistors and both known and unknown voltage sources. The user expresses confidence in their calculations using Ohm's Law (V=IR) and the formula for parallel resistors (R(parallel)=(1/R1+1/R2)^-1), but suspects that the MasteringPhysics platform has provided an incorrect answer. A critical error identified was mistaking a 1.0Ω resistor for a 1kΩ resistor, which significantly impacted the calculations. The discussion emphasizes the importance of accurately identifying component values in circuit analysis.

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  • Understanding of Ohm's Law (V=IR)
  • Knowledge of resistor combinations, specifically parallel resistance calculations
  • Familiarity with Kirchhoff's Voltage Law (KVL)
  • Ability to interpret circuit diagrams and component specifications
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  • Review Kirchhoff's Voltage Law (KVL) applications in circuit analysis
  • Practice calculating voltage drops across resistors in various configurations
  • Learn about common mistakes in circuit analysis, particularly regarding resistor values
  • Explore advanced circuit simulation tools for verifying calculations
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Students studying electrical engineering, physics students tackling circuit analysis, and educators looking to clarify common misconceptions in resistor calculations.

resigned
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Homework Statement


We are given a simple circuit with 4 resistors, a known voltage source, and an unknown voltage source. The photo is below in my solution attempt.

Homework Equations


V=IR, R(parallel)=(1/R1+1/R2)^-1

The Attempt at a Solution


I found the voltage drop over the given resistor, then used that voltage to find the current through the other resistor in parallel, which gave me the total current through the circuit.

http://imgur.com/HtJootR

My problem is I am pretty sure MasteringPhysics is wrong here. I included all of my work finding my answer, and then tested their answer to show that it is wrong. I am confident in my work but was hoping you could look it over before I go make a dodo of myself to my instructor.
 
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resigned said:

Homework Statement


We are given a simple circuit with 4 resistors, a known voltage source, and an unknown voltage source. The photo is below in my solution attempt.


Homework Equations


V=IR, R(parallel)=(1/R1+1/R2)^-1


The Attempt at a Solution


I found the voltage drop over the given resistor, then used that voltage to find the current through the other resistor in parallel, which gave me the total current through the circuit.

http://imgur.com/HtJootR

My problem is I am pretty sure MasteringPhysics is wrong here. I included all of my work finding my answer, and then tested their answer to show that it is wrong. I am confident in my work but was hoping you could look it over before I go make a dodo of myself to my instructor.

Their answers look fine to me.

Write out the voltage drops across each resistor. You know that they will potential drops in the direction of current flow, and that current flow can be either clockwise or counterclockwise. Perform a "KVL walk" around the loop assuming that the current flows in one direction and solve for the required Vba. Then do the same again assuming the current is flowing in the other direction.

By the way, that's a 1.0Ω resistor on the bottom, not a 1kΩ resistor.
 


gneill said:
By the way, that's a 1.0Ω resistor on the bottom, not a 1kΩ resistor.

Consarn it. I think that's the source of my problems. I didn't notice it had different units to the rest of them.
 

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