KVL Node Voltage: Positive vs Negative Assumption in Homework Solution

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SUMMARY

The discussion centers on the interpretation of node voltage in circuit analysis, specifically regarding the polarity of a 4V voltage source. The participant notes a discrepancy between their textbook's assumption of node voltage being positive and their professor's assumption of it being negative. This difference in assumptions leads to varying answers in homework solutions. The polarity of the voltage source directly influences the potential at node 'a', determining whether it is +4V or -4V with respect to the reference node.

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  • Understanding of KVL (Kirchhoff's Voltage Law)
  • Familiarity with node voltage analysis
  • Knowledge of voltage source polarity
  • Basic circuit theory concepts
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  • Examine the effects of voltage source polarity on circuit behavior
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cpatel23
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Homework Statement



ERcOJxY.jpg


Homework Equations



ƩCurrent(in) = ƩCurrent(out)

The Attempt at a Solution


KttP3fE.jpg
----In situations like that, my book takes the node to be a positive voltage when the voltage source is connected like above. For some reason my professor takes it to be negative, is this why my answer is different?


(sorry for the big pictures)
 
Last edited:
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The potential at node a with respect to the reference node depends entirely upon the polarity of the 4V source. The picture is a bit fuzzy around that source, but it appears that the "+/-" indicator shows "+" at the top. That would make node a +4V. It would also make the indicated answers incorrect.

If the 4V source polarity were reversed, then node a would be at potential -4V with respect to ground, and the given answers would then look good.
 

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