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I'm getting very confused about the inconsistency where some people say ground is always negative, and some say ground is always positive.

And some would say, electrons travel from the power source to the ground, but while some would say electrons travel from negative to positive. These two notions would be aligned and make sense if ground is positive, but not according to my Arduino instruction manual, since it's clearly drawn in pictures that the GND port of the circuit board links to the (-) column of the breadboard.

Moreover, according to physics, electrons flow from (-) to (+), so that sounds like anything coming from the (-) is acting as a power source? so which port in my Arduino does the power come from? the 5V port or the GND port? From my first impression, it's the 5V port that's supplying the power, since it's "5V." But is it one of those things where direction doesn't matter?

Just to make it easier for answering:

  1. Is it true that ground can be positive and can be negative, just a matter of preference and there's no "always?" And if yes, is negative ground the more popular preference?

  2. Does the energy come from ports like 5V? Or is it that labelled 5V doesn't mean that's where the power comes from?

  3. Do electrons in my Arduino flow from (-)(connected to GND) to (+)(connected to 5V), or the opposite?

Feel free to elaborate if you think it would make it clearer.

EDIT:

By 'power' I really meant energy.

Aryan Beezadhur
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Andy
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    1)Note that Voltage is measured across two points by definition(that is why Multimeter,oscilloscopes have two probes ).Ground is only a reference ,All other voltages are referenced with respect to this point .When you say a node in a circuit is at 5 V you are saying that it is 5 volts above ground . The actual potential at the ground point is immaterial as it is the voltage difference that causes the current. –  Nov 25 '15 at 18:12
  • Regarding the 5V, I am asking in the context of Arduino, there's a 5V port that i connect to the (+) column of the breadboard, my question is very simple, is that where the power comes from? And i understand that ground is a reference, but you're not answering my first question, is it true or is it not true that it can be positive and it can be negative? – Andy Nov 25 '15 at 18:14
  • Yes ,once we fix a ground potential any positive supply that sources current can be considered as a power source . –  Nov 25 '15 at 18:29
  • and by positive supply you mean negative supply in accordance to physics? – Andy Nov 25 '15 at 18:33
  • Nope ,the terminal which is positive . –  Nov 25 '15 at 18:35
  • yeah, i get that terminal is positive, but you used "positive" to describe supply in your previous comment. Are you saying that both the supply and the terminal are positive? – Andy Nov 25 '15 at 18:37
  • Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/32123/discussion-between-kishore-saldanha-and-andy). –  Nov 25 '15 at 18:38
  • @Andy People here have tried hard to answer your question as clearly as possible so you understand.Please consider accepting an answer. – Daniel Tork Dec 27 '15 at 16:22
  • This discussion is really incomplete without a mention of this: https://www.explainxkcd.com/wiki/index.php/567:_Urgent_Mission – Krunal Desai Dec 27 '15 at 19:31

7 Answers7

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(This comes up frequently; have you checked other questions on the definition of voltage?)

The key to understanding current is that it flows in loops. Power transmission is like a chain drive on bicycle. It's distracting to think of it "coming from" either of the terminals. Power is delivered by the current flow past a point.

Thinking about electrons is nearly always a distraction unless you're looking at semiconductors. As it happens, you're correct in (3): electrons flow from - to +.

The answer to your (1) is "yes" and your (2) is "question makes no sense".

pjc50
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  • I think question #1 could be answered much better (see my post). – Marco Nov 25 '15 at 21:03
  • By "power," I meant energy, not work done, I'll edit my question. – Andy Nov 25 '15 at 21:58
  • In that case I think what you're looking for is that the energy comes from the voltage field in the same way that it does from gravitational fields: dropping an object in a gravitational field causes it to accelerate, ie take energy from the field. Similarly a free electron in a voltage field accelerates - a free electron accelerated by a field of 1V acquires an energy of one electron-volt = 1.6×10−19J. – pjc50 Nov 25 '15 at 22:53
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1) is it true that ground can be positive and can be negative, just a matter of preference and there's no "always?" And if yes, is negative ground the more popular preference?

Ground / GND is just a node in your circuit. It's neither negative or positive. It depends on what you are measuring it against, remember: a voltage can only exist between two points.

To make this more clear I cite a site which explains it very good in my opinion:

How High is my Voltage?

Can an object have a certain voltage? No. Why not? Well, please tell what my distance is. What is my distance? That's a ridiculous question, because I didn't tell you my distance FROM WHAT. Voltage is a bit like altitude; it is a measurement made BETWEEN two things. My altitude is 300ft above sea level, but simultaneously my altitude is also 1cm from the floor (since I'm not barefoot,) and it's also 93 million miles from the sun. My voltage might be -250 Volts in relation to the earth, but it also might be billions of volts when compared to the moon. Volts are always measured along the flux lines of electric field, therefore voltage is always measured between two charged objects. If I start at the negative end of my flashlight battery, I can call that end "zero volts", and so the other end must be positive 1.5 volts. However, if I start at the POSITIVE end instead, then instead the positive battery terminal is zero volts, and the other terminal is negative 1.5 volts. Or, if I start half way between the battery terminals, then one terminal is -.75 volts, and the other terminal is +.75 volts. OK, what is the REAL voltage of the positive battery terminal? Is it actually zero, or actually +1.5, or is it +.75 volts? Nobody can say. The positive battery terminal can have several voltages at the same time. But this is no big deal, because neither can anyone tell you the battery's altitude! We can easily imagine the distance between two points, and we can also imagine the voltage between two points. But single objects don't "have" altitude, and single objects also don't "have" voltage.

Source: http://amasci.com/miscon/voltage.html (definitely go check it out!)

And FYI: If you are reading things like '+5V' or '-5V' it is usually referenced to GROUND. So +5V would be 5V above the GROUND node and -5V would be 5V below the GROUND node.

3) Do electrons in my Arduino flow from (-)(connected to GND) to (+)(connected to 5V), or the opposite?

The electrons move from the more negative side to the more positive side: GND to 5V. This is called electron flow.

Marco
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Conventional current flow from positive to negative was standardised long before the electron was discovered. The convention is still used and it works fine for most practical theory but we keep in mind that the electrons are moving negative to positive.

1) is it true that ground can be positive and can be negative, just a matter of preference and there's no "always?" And if yes, is negative ground the more popular preference?

Yes. For example, car electrical systems used to be positive ground, famously on the pre-1969 VW Beetle, but now the standard is negative ground.

You could consider the voltage a bit like floors on a building. In Europe, we agree that the ground floor is 0 or G, that floors above it are numbered positively and numbers below it are negatively. You now have the option of measuring everything relative to ground (the floor number) or measuring the difference in level between any two floors (the potential or voltage difference).

enter image description here

In the left image above our man is standing on Floor 2 relative to ground. The electrical analogy is that some point on the circuit is connected to ground / earth and by convention is zero volts and all voltages (heights) are measured relative to this.

An 'all above ground' building will have no negative floors. A bunker or underground car-park will have no positive floors.

If the building is launched off into space he has no ground reference and is free to number the floors any way he wishes, including have Floor 0 at any arbitrary point. This is analogous to having an electrically isolated circuit with no ground connection in that we can call any point 'ground'.

2) Does the energy come from ports like 5V? Or is it that labeled 5V doesn't mean that's where the power comes from?

As per the convention, we usually think of power flowing from + to - and the power coming from the + terminal on the power supply. In the case of your micro-controller it has an on-board 5 V voltage regulator and so the power is sourced from there.

3) Do electrons in my Arduino flow from (-)(connected to GND) to (+)(connected to 5V), or the opposite?

By convention the opposite. To aid schematic legibility we normally draw them with positive power rail on top. Voltage is decreasing as we go down through the schematic.

The following examples may help a little.

schematic

simulate this circuit – Schematic created using CircuitLab

The three schematics above show various ways of creating a buffer pre-amplifier, for example, for a guitar. Typically these would be built in a diecast metal box with a PP3 9 V battery for power.

1) The first configuration shows the battery negative connected to ground. (Since the audio signal can go positive and negative we need to bias the op-amp input to half-supply using the resistors on the non-inverting input. Capacitors block DC at the input and output.)

2) The circuit would work exactly the same if powered with positive ground.

3) A third option is to use a dual supply. Here we see that we can eliminate all the DC bias related components at the expense of a more complicated power supply.

The important points to note are that we can set the ground at any arbitrary point and we give all voltage readings relative to that point.

Negative ground is most common and, for example again, would allow a shared 9 V power supply to be used on a bank of guitar effects pedals.

Transistor
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The short answer is yes the 5v source is supplying power. Current flows when there is a potential difference, like 5v and ground 0v. However current will flow also if one point is more positive than the other. Let's say one point is 25v and another is 15v and you hook a wire to the points, current will flow, even tho one IS NOT GND. 0v. It's potential diff. Even with negative charges. Lets say one point is -25v , the other -15v, hook a wire and current will flow because -15 is more positive than -25.

Craig Cornett
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so which port in my Arduino does the power come from? the 5V port or the GND port?

Power is voltage x current and voltage is the volts between 5V and GND/0V. Current flows from 5V to 0V (electrons flow from 0V to positive but that's another story) and so you inevitably have the following: -

  • Voltage is related to both ports
  • Current is the same magnitude at both ports

This can ONLY mean that power arises due to both ports having a voltage and forcing a current thru a load.

Andy aka
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Ground is commonly used as the 0 V reference point in many schematics:https://en.wikipedia.org/wiki/Ground_(electricity).
It is not useful to use the ground as positive in your case(arduino),that's why it is negative here.Now for question 2 and 3,the "electric current flows from + to -" concept was chosen by convention for some reasons(see my answer to this question:Does electrical current flow from positive to negative or negative to positive?) ,but in reality it flows from - to +.Take a small DC motor for example and connect a battery to it.Note that it's going to rotate in the direction of the way of the electron flow(which is the real current flow),so you can predict which way it moves by the way you connect your battery to it,judging after the current flow.

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Daniel Tork
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1) Ground is by default 0, which is neither positive nor negative.

For a single supply system, ground can be more negative than the supply terminal -- for example, a system with GND and +5V. Notice that we are specifically referencing ground to +5V in this statement, which is not the normal convention. So unless specifically stated otherwise, ground is the reference and is zero.

Or ground can be more positive than the supply terminal -- for example, system with GND and -5V.

2,3) A circuit element is supplying power when current is flowing from its positive terminal to its negative terminal externally. That is, electrons flow from its negative terminal to its positive terminal externally.

So for an Arduino, which is using power, the current or electron flow is opposite from the above paragraph. Here are two ways to describe the flow, which form a complete loop -- electrons flow from the negative terminal of the Arduino internally to its positive terminal; electrons flow from its positive terminal externally to its negative terminal. (By the way, it is much better to just think current instead of electron flow in circuit analysis, because that is simply how everything are done.)

rioraxe
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