# Voltage Concept

#### AndrieGnd

Joined Jun 25, 2019
52
Hello gentlemen ! what's up?
I'm started newly to studying electrical engineering and I really finding it hard every time I solve and deal with circuit to determine if there's a current on on the branch or not, I'm using analogy to determine if there's a voltage on the branch if there's a current, but what's confusing me that It takes for me much time to determine if there's current or not.
for example lets assume I have GND connected serial with resistor and through the resistor there's no current, then we have the same voltage .. but why!? it looks simply yeah .. but I do equations to prove why voltage is the same.... what's I'm asking about .. is there any more senseable analogy to take it in advance for determining if there's the same "voltage" or not on the branch?! for instance by that analogy that you give me can immediately determine if I still have the same voltage or not on the device! -- it would be appreciated if you implicitly explain the concept of voltage and current, relations between them in aspect of senseable real life analogy --

thanks alot.

#### Alec_t

Joined Sep 17, 2013
10,354
Welcome to AAC!
Are you familiar with Ohm's Law? If not, research that.
If current is flowing through a path which has electrical resistance then there will be a voltage (= potential difference) across that resistance. Even a wire has some resistance.
If there is no current then there will be no voltage developed, so the electric potential at both ends of the path will be the same. Conversely, if the potential difference is zero then no current will flow.

• AndrieGnd

#### KeepItSimpleStupid

Joined Mar 4, 2014
3,597

If there is a potential difference (difference in voltages), there is a current. Simple enough.

BUT, instruments that measure voltages disturb the circuit. A voltmeter might look like you just added a 10 M-ohm resistor in parallel with what you measured.

Similarly, real world ammeters are not usually of the "zero resistance type" or a "feedback ammeter", You place a small values resistor in series with what you measure.

Current doesn't really "flow". Charge does. Now is the time to introduce "conventional current". We get a positive number when we attach the (-) lead to the reference and the (+) terminal of our voltmeter to a higher voltage potential. Ben Franklin got the sign of the charge on an electron wrong. Most of the time it does not matter.

• AndrieGnd

#### AndrieGnd

Joined Jun 25, 2019
52
I'm familiar with Ohm's law, but I want to grasp the concept of voltage/current to implicitly use this analogy to analysis "in a handshake" the circuit .. without using formalization of equations

#### MrAl

Joined Jun 17, 2014
6,454
I'm familiar with Ohm's law, but I want to grasp the concept of voltage/current to implicitly use this analogy to analysis "in a handshake" the circuit .. without using formalization of equations
Hi,

Electrical circuits are sometimes intuitive but sometimes they can be tricky so end up being anti intuitive.
That's why we have things like Nodal Analysis. You do the analysis, you solve for the nodes, etc., and then you begin to understand the circuit.
Sometimes even that's not quite enough we end up needing general circuit theory also which goes into the basic operating principles that show the important features of some circuits like resonant circuits.

So it's a learning process and it takes time to absorb everything. There are a few short cuts but a well rounded education is much better. The more math you have under your belt the farther you can go with the theories.

#### djsfantasi

Joined Apr 11, 2010
5,577
I'm familiar with Ohm's law, but I want to grasp the concept of voltage/current to implicitly use this analogy to analysis "in a handshake" the circuit .. without using formalization of equations
“In a handshake” means what to you? It means nothing to me.

In a linear circuit, Ohm’s law is all you need. Voltage is a relative measurement between any two points (modes).

You can arbitrarily assign any node to have a zero voltage with respect to your measurement. Then measuring a second point, the value you measure is the voltage differential between the two points.

Consider a circuit connecting a 6VDC supply positive through two resistors, R1&R2), 100Ω and 200Ω, then to ground of the supply (negative). Humor me and label the node between the resistors node_A.

Measuring voltage from the top and bottom nodes gives you 6V. What does Ohms law tell us? V=IR in this case is
6=I*300​
Hence
I= 6 /300​
Or
I=20mA​

Measuring from node A to the positive supply gives you... 2V. Why?

Current is constant through a circuit (series circuit). So it’s 20mA through the 100Ω resistor. What does Ohms law tell us?
V=IR
V=0.020*100
V=2V​

Now, let’s consider the voltage between Node_A and ground. There’s two ways of calculating this. The simple way is
V=V1+V2
6=2+V2
V2=4​
where V1 is across the first resistor (from supply positive snd node A). and V2 is the voltage across the second resistor (from node A and supply ground(negative))

Or I said you could calculate it another way. Once again, the current is 0.020A. And the resistor is 200Ω.
V=IR
V=0.020*200
V=4​

Once you get the hang of it, it’s not difficult.

• narkeleptk

#### WBahn

Joined Mar 31, 2012
24,674
I'm familiar with Ohm's law, but I want to grasp the concept of voltage/current to implicitly use this analogy to analysis "in a handshake" the circuit .. without using formalization of equations
Voltage, by definition, is the change in potential energy that a charged particle (per unit charge) would experience in moving from one place to another. It's like the height on a sloped surface. If you have a flat board that is sloped so that one end is higher than the other, then a ball placed at the upper end will roll toward the other. If you place the ball on the board and it just sits there, then you know that the board is level meaning that both ends are at the same height. The same is true with electrical nodes connected by a resistor; if no current is flowing, then you know that the potential energy of charges at one node must be the same as at the other, otherwise they would be flowing.