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") โ 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. ๐คญ
Explain it to me as if I was five. ๐ถ
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.