I am reading up on logic circuits, families and levels because it's fun. I have no formal education in physics, computing or electronics.
For power supplies, sometimes one of the supply rails is referred to as ground (abbreviated "GND") – positive and negative voltages are relative to the ground. In digital electronics, negative voltages are seldom present, and the ground nearly always is the lowest voltage level. In analog electronics (e.g. an audio power amplifier) the ground can be a voltage level between the most positive and most negative voltage level.
I know from previous reading, that electricity - at least when it comes to direct current, but perhaps even when it comes to AC? - has a way in ("line"?) and a way out ("neutral" or "ground"? - disregarding for a second the fact that ground also carries current in case of a ground fault).
Again, from previous reading, I know that we work computers by either supplying them voltage or not (or in some circuits a higher voltage and a lower voltage). In any case, it's a choice between one or the other, since that is what we are trying to represent: boolean true or false.
So, what is this "negative voltage"? Is this a figure of speech or can voltage actually have a negative value? The part from the article that I quoted above states in relativistic terms, that "the ground can be a voltage level between the most positive and most negative voltage level" (italic text by me), which makes me assume "yes". But if voltage is electromotive force, how can it be negative? I amusingly imagine a force "sucking" the current backwards. 🤭
Explain it to me as if I was five. 👶
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 +.
May I just ask, what "virtual" means here? Non native speaker. 🙏
You’re welcome, I’m glad this explanation made sense, I’m also non-native :D
They are like places where electrons could be, you could also call them „electron holes“. If an electron flows through a conductor, it kicks off other electrons bound to atoms taking their place, which then become free electrons, it’s like a chain reaction without the amplification thing. But they aren’t „physical particles with a positive charge“
You could say electrons flow from left to right but you could also say that holes flow from right to left. You may hear an engineer or electrician say that electrons flow from + to -, because it’s just easier to communicate.
Most components like resistors don’t care about current direction anyway. But semiconductors like diodes do, they’ll heat up very quickly if connected in the wrong way.
For most household appliances this is completely irrelevant because the sine potential (and the current flow it causes) change directions every (depending on where you live) 10ms. Yes your phone is semiconductor based, but your phone charger rectifies the outlets AC current into a DC current with a defined direction.
Often times we use earth ground as the source of 0V. Can you end up with differences in potential on different "earth grounds"?
Safety disclaimer: Treat this as a thought experiment, some actions which I describe are dangerous in reality. Never experiment with electricity if you’re unsure if what you’re doing is safe.
To avoid some confusion which might occur otherwise: I’m using technical conventions and I’m thinking about electrons flowing from hills (+) to valleys (-).
Take the words earth and ground literally, it’s really a thick metal rod which gets hammered into the ground when a house gets built.
A voltage source like a battery or a generator creates a difference in electric potential between its poles (by separating charge).
Think of hills and valleys separated by a solid wall on isolated islands floating in the sky for some reason… 😅 The islands are of arbitrary height and free floating, but their height difference is fixed. On each of them you could do the ball on a hill experiment and it would yield the same result.
You can connect the hills and valleys of each island by attaching a highway with its own wall. This is the equivalent of connecting the poles via a resistor (lower electric resistance means more and bigger holes in the wall, hills/valleys will deplete faster).
You could also connect these islands in a way so that the valley of one and hill of the other touch. If you use low resistance wires there is nothing stopping electrons to freely flow from one island to another, whatever height difference there initially was between the valley and hill of the two islands, instantly drops and the islands get pulled together. But no electrons actually flow (no height difference is driving them), no hill and valley of any individual island gets depleted, no energy transferred - that’s essentially what chaining 9V batteries to yield multiples of 9V is.
If you ground one pole of a generator, you pull the island toward the earths surface, which in itself can be considered a flat, but practically infinite valley/hill. Earth acts as a kind of mass storage for electrons not changing its height much when letting charged particles flow into it or vice versa.
So if you had two grounded generators:
If you were to connect the hill of the 200V generator to the valley of the 100V generator, the valley and hill of the 200V generator would be directly connected by the ground resistor (and its own ground resistor but that can be neglected in this example), pulling the ground pin of the 100V generator to 200V and its hill to 300V above earth - and that’s the answer to your question. In theory every grounding point isn’t actually a grounding point, but we do our best to keep resistance as low as possible so that we can safely touch metal objects in our houses.
Oh and things like „instant depletion transferring energy“ essentially means short circuiting a voltage source, so do not experiment with this, even if it’s low voltage like 9V batteries, they can start a fire too and in practice there are also chemical hazards. In the generator example a fuse would blow if there was one, stopping the depletion and preventing a fire or a molten generator. Use circuit simulators like falstad.