Is the Unknown Circuit Component a Resistor or a Voltage Source?

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Discussion Overview

The discussion centers around identifying an unknown circuit component in a homework problem, specifically determining whether it is a resistor or a voltage source, and finding its value. The analysis involves applying Kirchhoff's Voltage Law (KVL) and Kirchhoff's Current Law (KCL) to the circuit.

Discussion Character

  • Homework-related, Mathematical reasoning

Main Points Raised

  • The initial analysis using KVL on the outer loop led to a current of 2A.
  • Applying KVL on the inner left loop resulted in a current of 1A.
  • KCL was used to find the current through a 20-ohm resistor, which was also 1A.
  • A calculation suggested that the unknown component could not be a resistor if it resulted in a negative voltage, leading to the conclusion that it must be a -10V source.
  • Some participants confirmed that the analysis and the resulting currents would hold if the mystery component is indeed a -10V source.
  • There was a reiteration of the reasoning that knowing the voltage across the mystery component and the 20-ohm resistor allowed for the correct calculation of currents, which could then disprove the component being a resistor.

Areas of Agreement / Disagreement

Participants generally agree on the analysis presented, particularly regarding the conclusion that the unknown component must be a -10V source based on the calculated currents. However, the discussion does not explicitly resolve whether the component could be a resistor under different conditions.

Contextual Notes

The discussion relies on the assumptions made during the analysis, particularly regarding the behavior of the unknown component and the implications of the calculated voltages and currents. There may be limitations in the assumptions about the circuit configuration and the definitions of voltage sources and resistors.

Who May Find This Useful

This discussion may be useful for students studying circuit analysis, particularly those interested in applying KVL and KCL to identify circuit components and their values.

jendrix
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Homework Statement



The circuit has an unknown component that is a resistor or a voltage source, find which one it is and it's value.




Homework Equations



V=IR, KVL, KCL



The Attempt at a Solution



I first used KVL on the outer loop:

14-2I1-10=0

I1=2A

Then on the inner left loop

14-4V-10I2=0

I2=1A

Then KCL to find current through 20ohm resistor of 1A

Inner loop on right hand side

10I2-1x20-?+0

? =-10V

Answer:

Due to the direction of the current the -10v couldn't be from a resistor as it would result in a positive 10v over the resistor.Instead it must be a -10v source.


Does this look correct? If this was a -10v source wouldn't that disprove all the currents I found?

Thanks

2h305f5.jpg


 
Last edited:
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Your analysis looks fine. The currents would be fine, too, when the mystery component is a -10V source.
 
Thank you, so if I understand this correctly, because we knew the 10v across the mystery component and 20ohm resistor this allowed the correct currents to be calculated.Once we knew these currents we could disprove the mystery element being a resistor?
 
jendrix said:
Thank you, so if I understand this correctly, because we knew the 10v across the mystery component and 20ohm resistor this allowed the correct currents to be calculated.Once we knew these currents we could disprove the mystery element being a resistor?

Yes, that is so.
 
Thank you
 

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