Simple Vector Notation Standard

[electronicsfreak]

Alright, so my apologies for asking such a simple question, we're going straight back to the basics here. However, I have become quite confused due to inconsistencies within the material provided for one of my courses while studying for our final exam, and I would love to get some input from the community.


So, to those of you whom are willing to respond, I have provided two separate images that correspond to one-another. To keep my question simple and straight forward to the concept I'm looking for, we're gonna keep this provided element resistive.






With regards to the two vectors provided, would you consider the Voltage to be defined as V[SUB]AB[/SUB] or V[SUB]BA[/SUB]
also, same with our current, would you consider it to be defined as I[SUB]AB[/SUB] or I[SUB]BA[/SUB] ? --edited with the solution

From my understanding, it really doesn't matter so long as one remains consistent. However, as far as what is considered industry standard, I'd love to hear your input

Thank-you all in advance

 

[electronicsfreak]

Out of curiosity, for those viewing, is this just such a simple question that it's not even worth the time, or is it actually stumping those of you just like myself? I realize this goes to a pretty low level, but heck even the examples in my textbook are contradicting. (by textbook, I really mean printed notes from my professor)

Anyways, regardless, I'd still love to get some input, even if it is just more suggestions of what to put in a search.

 

[Ratchit]

efreak,

I know of no "industry standard" for a directed line. Voltage is not a vector. Neither is current in the context you are using. I believe you want to refer to those two lines as phasors.

Ratch

 

[MrAl]

Hi,

The convention is usually the first letter is the most positive. Vab would mean the voltage across a and b where a is the most positive. An arrow that 'looks' like a vector is sometimes used to show the voltage where the tip is the positive. The arrow would then be marked "Vab". So in your drawing this arrow would be pointing east to west, the tip is 'a' and the tail is 'b'. The current arrow points in the opposite direction.

As for current, two nodes are not necessary so it really should be Ir where r is the object that has I amps through it. If you need to show direction then you would still follow the first letter most positive convention. That means Iab would be conventional current flow from a (most positive) to b (most negative), where again the most positive is in reference to the voltage not the current even though it is a current being specified.

I almost forgot to mention, that sometimes the polarity is already shown using plus and minus signs, and the voltage is then given as Vab or Vba, which mean opposite polarities. For example, if the plus sign is at 'a', then Vab means a positive voltage, and Vba means that same voltage but with sign reversed. So say we have a 10 ohm resistor drawn horizontally, with the left side with a plus sign and the letter 'a' and the right side with a minus sign and the letter 'b', and we have 1 amp flowing through it. Since the left side already has a plus sign, that means the left side is more positive than the right side, so Vab would be Vab=+10v, and Vba=-10v.
If we were to draw an arrow, we would probably draw it from east to west where the tip is positive, then we can label that arrow as Vab or as +10v, but it is possible to draw the arrow from west to east and label it "-10v".
So the rule then is that polarity signs (plus or minus) have the highest precedence for showing the polarity, with arrows being next if there are no plus or minus signs. Actual voltage levels referenced to ground or to the object are good too.

 

[electronicsfreak]

Thank you for the help guys, and yes you are correct, phasor notation is what I was referring to. That arrow notation you describe MrAl is mostly what my professor uses in class to show a voltage rise be it an input to a motor, output from a generator, etc. We also typically denote current as Ir,Il, etc. I had simply come upon a practice problem regarding to current using nearby nodes.


This leads me to believe a final answer provided with that described practice problem may have an error within it, As I can get the negative of the provided solution, or simply the same magnitude 180° out of phase. I'll double check my work before claiming anything though.

Thanks again fellas