# Voltage Point Problem.

#### MaxMichaels

Joined Nov 30, 2021
28
Greetings. I’m working on a example on finding the voltages between the various points. Now if you look at figure 2.13 A) & B) I need to find the voltages between points A & C in both figure examples. Now in Fig.A) the voltages between A & C is zero, but in FigB) the voltage point is 3. Now in one example there is a ground symbol and the other their isn’t. I’m assuming that’s what gives the voltage change but I still don’t understand how the voltages in between A&C is 3 and the other is zero. Help.

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#### ericgibbs

Joined Jan 29, 2010
15,348
hi Max,
Welcome to AAC.
As this is homework, please post your best attempt, we can then help.
E

#### MaxMichaels

Joined Nov 30, 2021
28
hi Max,
Welcome to AAC.
As this is homework, please post your best attempt, we can then help.
E
So as I was attempting to solve it, I got confused when I saw that both answers are different because, usually, most dc ground circuits, the ground reference point is usually placed at the negative terminal of the voltage source. But figure A has no ground symbol, so how would I attempt to find voltages between A&C in figure A? Do I assume that ABCD are stacked on top of each other? And if so that would mean that ground, is point D. And if figure B, ground symbols are present, so I can assume that the answer, voltages between points A&C is 3 Volts, for figure B because the ground symbols means that the voltage reduces all the way to zero volts. And 12V from 9V leaves 3V. But that’s what I assumed the answer would be for figure A. But the answer is 0. So now what must I assume for figure A? How and why are the answers different?

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#### ericgibbs

Joined Jan 29, 2010
15,348
hi Max,
Consider this.
How could current flow through the voltmeter.?
E

#### MaxMichaels

Joined Nov 30, 2021
28
current flows through the voltmeter by connecting the voltmeter to the negative and positive terminals of the battery

#### ericgibbs

Joined Jan 29, 2010
15,348
hi,
No.
Where is the conductor between B and D,,, there is no connection, so no current flows around the circuit and through the meter , so Zero Volts shown on the Meter.

Do you follow.?
E

#### MaxMichaels

Joined Nov 30, 2021
28
yes, i follow you. so what you are saying is, in figure B, the "ground" symbols, mean that B&D have conductors/wires connected. so there is flow. meaning we will get a volt reading of 3 in figure b

#### ericgibbs

Joined Jan 29, 2010
15,348
hi
Yes.
Fig B, A to C will read 3V

That's the algebraic sum of 12V and 9V, in opposing polarities

E

So what is Voltage B to D.???

Last edited:

#### MaxMichaels

Joined Nov 30, 2021
28
in figure b voltage B to D would be zero because we are connecting the voltmeter to the ground source. and ground sources are normally zero

#### Jony130

Joined Feb 17, 2009
5,316

#### MaxMichaels

Joined Nov 30, 2021
28
ok, so i was correct, but was my reasoning correct?

#### ericgibbs

Joined Jan 29, 2010
15,348
ok, so i was correct, but was my reasoning correct?
hi MM,

in figure b voltage B to D would be zero because we are connecting the voltmeter to the ground source. and ground sources are normally zero

The Ground or Common or 0Volt symbol is usually taken as the measurement reference point, when measuring voltage points within a circuit.

So all the points in the circuit with that same symbol are effectively connected together via the 0V line.

Take care when reading or using that type of symbol, there are various versions of the symbol which mean different connection points.

E

Look here.

And here.
https://www.ni.com/en-gb/support/do...ignal-grounding--terminology-and-symbols.html