Understanding of Voltage potential

[PhysicsTest]

TL;DR Summary

I want to understand the voltage potential

I am bit confused with voltage potential terminology again to basics

When it is referred as Voa it is Voltage of "o" wrt "a". Is it correct?
But other major question is

as per the document

I would have written KVL as Voa - I1 * Z = Vn. I am really confused with notation used.

 

[Tom.G]

TL;DR Summary: I want to understand the voltage potential

When it is referred as Voa it is Voltage of "o" wrt "a". Is it correct?

Since all of the measurements are relative the the "O" node, i"O" is the 'reference' node (or 'common' node), this is often referred to as 'Ground', even if it is not connected to the actual Ground or Earth.

So V_OA is Voltage of "A" wrt "O".

In general, the first subscript (in this case 'O') is the Reference point and the second subscript is the point being measured. Another way to remember it is 'from' and 'to' for the subscripts.

Hope this helps!

Cheers,
Tom

 

[DaveE]

I would have written KVL as Voa - I1 * Z = Vn. I am really confused with notation used.

Me too. But as long as you are consistent with the sign definitions the equations will give you the correct answer regardless.

 

[Steve4Physics]

I would have written KVL as Voa - I1 * Z = Vn.

I too agree. But (though not an electrical engineer) can I add this.

Using $V_{on} = V_{oa} + ZI_1$ etc. is not consistent with the assumed current-directions shown in the diagram. It is not the usual practice in my experience. I would (as an ex-teacher) mark it wrong.

When setting up the equations, the signs in the equations must be consistent with the assumed current directions.

For example, in more complicated circuits with 'loops', different currents can flow through the same component. E.g. there might be $I_4$ flowing through a resistor in one direction and $I_5$ flowing through the same resistor in the opposite direction. In such situations, not following strict rules about the use signs can lead to errors. Is thecurrent through the resistor $I_4+I_5, I_4-I_5, -I_4+I_5$ or $-I_4-I_5$? You need to be able to pick the correct one!

 

[DaveE]

Since all of the measurements are relative the the "O" node, i"O" is the 'reference' node (or 'common' node), this is often referred to as 'Ground', even if it is not connected to the actual Ground or Earth.

So V_OA is Voltage of "A" wrt "O".

In general, the first subscript (in this case 'O') is the Reference point and the second subscript is the point being measured. Another way to remember it is 'from' and 'to' for the subscripts.

Hope this helps!

Cheers,
Tom

In my experience, you will not find a consensus either way with this definition. The important thing is to be consistent within a single analysis and to understand as best as possible from the context which definitions are being used.

Again, the definitions of various polarities can be arbitrary, but strict consistency in their application is mandatory.