No Stupid Questions

I think there’s a very physical but also intuitive way of thinking about this which eliminates all of the confusion (even with current conventions)

Forget about voltage and let me introduce potential Think about that as a landscape, its height changes and can be mapped in a height map. It corresponds to the „arbitrary energy level“ a particle on which a force may act. Imagine a ball on a curved hill: when ignoring friction and elasticity, the ball has contact with the plane at a singular point and will begin to roll down the hill. That’s what electrons do in a electric field (they rise to the top actually but you may think about current as „virtual“ positive particles which engineers do all the time. The „sea level“ is usually defined as 0V (the potential is also measured in volts)

Now the concept of voltage becomes nothing more than a height difference. In my opinion this beautifully explains concepts like Kirchhoffs voltage law: walk a circle on earths surface and measure your net height change… it’s always 0.

So to finally ( :D ) answer your question: a negative voltage is a negative height change. You just switch the terminals so that charge flows in the opposite direction.

Also current conventions become less confusing, because there is something all scientists and engineers can agree on: a voltage source creates a hill and a valley in its electric potential, the hill is + and the valley -, engineers think about current as virtual positive charge which will move from + to -, scientists will think about it as electrons moving from - to +.

Voltage is always a difference between two points. It is not absolute - it depends on where you measure from.

When we measure voltage, we always choose a reference point (often called ground or 0 V).

If a point has more electric potential than the reference → voltage is positive

If a point has less electric potential than the reference → voltage is negative

So, a voltage is “negative” only because of the chosen reference point.

Example

Imagine a battery:

• the positive terminal is higher potential
• the negative terminal is lower potential

If you measure like this:

• Red probe on +, black on − → +9 V
• Red probe on −, black on + → −9 V

Same battery, different reference → different sign!

• Voltage is always relative
• Negative voltage means: “This point is lower than the reference point”
• The same physical voltage can appear positive or negative, depending on how you measure it

The lowest geographic place in the United States is Badwater Basin in Death Valley. It's altitude is -282 feet. That's a negative altitude.

What does that mean? It means that Badwater Basin is below the 0 altitude level, which we have chosen to define as "mean sea level." We could have chosen a different altitude too be zero, but we didn't.

If there is a pathway from the sea (at Mean Sea Level) to Badwater Basin, then the water will flow to the basin, because it would have a lower potential energy in the basin.

Voltage is potential difference. It is always the difference in potential between two different points. But like altitude, we often don't say one of the two points out loud because it's a common reference level.

A positive charge in a vacuum will gain speed (kinetic energy) moving from a higher potential to a lower potential, because its potential energy goes down. It doesn't matter whether it's going from +9V to +5V versus 0V to -4V. The change in potential is the same.

Generally, my understanding, is there is a "flow" and a negative reading would be flowing the other direction. Thinking about a multimeter - it usually expects flow from red to black, but if you swap those around, you get a negative number as it flows from black to red.

The actual number is usually (not always) the important part - the potential difference between the two ends or something like that. That difference is going to behave similarly no matter which direction, but we assigned it numbers like that to make talking about voltages easier.

I don't think anyone referenced audio applications yet, the concept might be easier to grasp if you visualise it with a speaker.

Sound is just a particular way of moving the air, so a speaker at rest is just a cone sitting in the middle of an electromagnet, not protruding, just resting ready to be pushed out or pulled in according to the desired sound, this is the 'rest' state, or 0v.

Amplifiers are provided with a positive voltage to be able to pull the speaker cone one way, and a negative to push out the other way, with a reference (or 'rest') in the middle. This voltage, often +12v 0v -12v, is provided be a transformer that has been tapped in the middle. But if you use measure accross the tranformer, you will measure +24v, because that's the total voltage potential of the circuit.

If you switch your measuring probes the other way around you'll see -24v on your meter, did anything fundamentally change when you measured the other way around? No! It's just your reference point that changed.

Others have already answered, but one thing I think helps a lot in understanding electricity is to think of it as water. Water running through a hose behaves exactly the same as electricity running through a wire.

The amount of water running through the hose is similar to the amount of electrons running through the wire. We call this current, and measure it in Amperes. Whenever you read amperes think about the flow of material through the medium. Can this value be negative? Sure, it means the current is flowing in the opposite direction.

If one end of the hose is higher than the other the water will flow from the taller part to the lowest one. Measuring how tall one part of the system is compared to another tells you a what potential difference there is there. We call this Voltage and measure it in Volts. Whenever you read volts think about the potential of movement, if there is a 5 Volt difference between two points in your circuit, connecting a wire between those points will produce a flow, just like how if one reservoir is higher than another connecting a hose between them will move water around. Can this value be negative? Sure, it means the other side has more potential energy.

If the inside of the hose has a rougher surface water will have more difficulty flowing through there than if it's smooth. We call this resistance and measure it in Ohms. Whenever you read ohms think about how difficult it is for the current to flow through. Conversely Mhos (OHM spelled backwards) is how easily current flows through the material. Can either of these values be negative? Not usually, but things can behave as if they had a negative resistance, e.g. an amplifier, which in our water analogy is a device that uses a small water flow to control the doors for a larger door, if you have 1 drop per second it let's put 1L per second on the other side, so it can be seen as something that increased the water flow, therefore negative resistance.

Now you want to move a wheel with your water, for the water this wheel is seen like a hose that's harder to move through, so it offers some resistance. If you don't have enough water flowing it won't budge. You can move the wheel ba raising the other side of the hose, this increasing the speed the water flows and giving it more energy, or you can do the same by putting more water in the hose thus increasing the current. Therefore we need a unit to measure how easily the water at a given point can move a wheel. We call this Potence and measure it in Watts or VA (Volt-Ampere). Whenever you see Watt think about the amount of energy the el electricity has at that point.

Lamps have a measure in Watts, because they're like a wheel that the water will move, and they're letting you know how much water energy you need to throw at it for it to move, you can use high amperage low voltage, or high voltage low amperage to get to this result. Because both the Voltage on your house, and the resistance of the lamp are fixed values, you can calculate the resulting amperage and wattage.

I think I went a bit off topic, but I hope this helps clarify some of those concepts.

Voltage is like air or water pressure, and there is an ambient pressure in a system (like the atmospheric pressure) that we arbitrarily call zero. Negative (*) voltage would mean that there is enough voltage/pressure to force electrons to be emitted to ground (ie the ambient pressure) and positive (*) voltage would mean that electrons can be accepted by ground.

*) Negative and positive are a bit confusing because we originally assumed the charge carrying particle was positive, but the electron turned out to be negative; there were some historical quirks as a consequence and some things are backwards from what you would anticipate, and sometimes I get them wrong.

In simple terms, a Voltage is the difference in the electric potential between two points or in other words, a difference in how much electrons are attracted to one point by comparison to how much electrons are attracted to another (and, depending on said different, they will move in towards one of those points or not move at all is the difference is 0)

So technically you can't actually have a Voltage with just one point.

So why do you hear Voltage mentioned as being a characteristic that can be measured at one point of a circuit?

Well, what it's done in practice in Electronics is for example to treat one side of the power source as being the reference to measure voltage (say, the negative side of the battery) - which we the call Ground - and then we can say there is a "voltage" at any point in the circuit as a shortcut for the difference in electric potential between that point of the circuit and the one we conventioned as being the reference one.

(Notice how when using a Voltimeter or a Multimeter in Voltage mode to measure the voltage you need to used TWO probes and are told to put the black probe on a Ground line)

So because this reference point when measuring the different in electric potentials between two points is a convention, it's perfectly possible to use a different convention so that some or even all "voltage" values we negative.

When measuring voltage it is important what reference level you have, conventionally electrons flow from positive to negative, so if you switch the probes it'll be negative, in a larger circuit you choose a way to navigate and you take the sign and calculate, if it's positive or negative. PCB are not a good way to see it as they usually are constrained by size and they can have multiple layers and hidden paths also alternate is much more complex to work with.

Also be careful around power supplies PCB, they can have large capacitors that can deliver dangerous voltage.

If you want to get into electronics I suggest starting with DC current, much simpler and you can make some nice projects with arduino or other SBC

Negative voltage means you have the probes swapped.

I amusingly imagine a force "sucking" the current backwards. 🤭

If you think of a positive voltage as pushing then it is not anymore inaccurate to think of a negative voltage as pulling. At least if you think in terms of DC, which is what power supplies will typically give you.

Voltage is all relative. The sign just shows the direction of flow. If you plug a volt meter in backwards it will show a negative voltage. That means the current will flow from the negative to the positive terminals.

If you have three terminals, let's say A, B, and C. If you measure 12V between A and B. Then 24V between A and C. Then you will also be able to measure 12V between B and C. Or -12v between B and A. Or -24 between C and A. The direction matters.

You could label any of these as ground it makes no real difference to the system. Only how you talk about it. Without a ground label then you would not say C is at 24V as it has nothing to compare to. If you pick A as ground then it is said to be 24V, but if you pick B as ground then it is said to be 12V. If you pick C as ground then it is 0V. So when we say a point is at a voltage then that is implied that it is that voltage relative some other point we decided was ground.

Things get a lot more complicated with AC as electrons move back and forth in the wire they don't have the same direction as they do in DC.

Voltage that isn't fun to be around because it's always such a downer.

You take some point of your circuit, call it "ground" and define the voltage there as 0.

If something has a higher voltage than it, than the voltage is positive. If the voltage is lower, than it's negative.

Also, you are mixing energy distribution names with your voltage references. Your ground wire has the same potential as the actual ground (the stuff made of dirt where your house is built). We usually define it as the ground in circuits that are connected to it, but you'll be surprised by how unusual it is to connect circuits to it.

But if voltage is electromotive force, how can it be negative?

The charge moves from higher to lower voltages. In a wire, that means that electrons move from lower to higher voltages. The absolute value of a voltage is meaningless, you will only ever use differences between them.

Its voltage that just feels tired in itself, just wants to be alone and not push any charge.