Circuit Analysis: Solving the Mystery of V3's Voltage Directionality

AI Thread Summary
The discussion revolves around understanding the voltage directionality in a circuit diagram, specifically why voltage V3 is labeled as negative with respect to the power source and positive with respect to ground. Participants clarify that the labeling is primarily for educational purposes, indicating that a negative value for V3 simply means the initial guess about its polarity was incorrect. They emphasize the importance of rigor in algebra and the need to maintain meticulous attention to detail when applying Kirchhoff's Voltage Law (KVL) and Kirchhoff's Current Law (KCL). The consensus is that incorrect assumptions about direction can lead to negative results, which are still valid in terms of polarity. Overall, the discussion highlights the significance of understanding voltage signs in circuit analysis.
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Hi guys. Really elementary question here, I've been kicking myself for ages trying to figure this out, but I suppose everybody needs a little nudge sometimes.

I have been staring at this circuit diagram:

tsVhvmk.png


From this page:

http://www.facstaff.bucknell.edu/mastascu/eLessonsHTML/Basic/Basic5Kv.html

which is basically a rundown of Kirchoff's Voltage Law, and I have been wracking my brain for why voltage V3 is labeled (-) with respect to the power source and (+) with respect to ground.

If I follow a current running from the positive terminal of the power source, then it splits up into the two branches to go through R2 or R3 and R4, respectively. The directionality of the voltage (to my intuition) should be the same for V3 as it is for V4. It is dropping voltage, not adding to it.

Thanks for any help you can provide!
 
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I'm guessing it was done to teach a concept. I would never label it that way in real life.

In this case, all it means is that V3 is probably going to be a negative number (and V4 will be positive).
 
Second for post #2.
When sliderules roamed the Earth and i was being taught KVL , teacher made it a major point to write those little polarity + & - signs .
He said emphatically: "If polarity is not intuitive by looking, just guess - if you guess wrong you'll get a negative number for that one. It only means you guessed wrong, your answer will be correct for the polarity you've shown. "
That's why it is so important to be rigorous and neat in your algebra. No shortcuts or you'll start dropping signs.

old jim
 
Okay, so it's just for the sake of making a point. Thanks you guys!

I just want to check that it's the same for KCL: pick your current directions, and if you're wrong, then you'll get a negative sign for that particular branch of current.
 
Also, "when sliderules roamed the earth". lol.
 
Yes, same for KCL.

Meticulous attention to detail will pay off down the road. Form your good habits early.
 
Thank you sirs, I will watch my signs with care.
 

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