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") β 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. π€
Explain it to me as if I was five. πΆ
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 β voltage is positive
If a point has less electric potential than the reference β voltage is negative
So, a voltage is βnegativeβ only because of the chosen reference point.
Example
Imagine a battery:
If you measure like this:
Same battery, different reference β different sign!
Sic. This explanation is clear as day. Thanks!!!
If you (or anyone else) wants to check their understanding of voltage as the difference between two electric potentials, here's a couple exercises I stole from a text book:
(Note: Electric potential is also measured in Volt.)
A battery has a constant voltage of 1.5V between its plus and its minus pole. What is the electric potential of the minus pole compared to ground potential when:
Solution
The battery is not connected to ground. Therefore, no statements about the electric potential of either pole can be made.Solution
Because of the connection, the electric potential of the minus pole equals that of the ground, which is by definition 0V.Solution
Now the potential of the plus pole equals that of the ground. We know that the voltage difference between the plus and minus pole is 1.5V. Since this difference is measured by subtracting the potential of the minus pole from the potential of the plus pole the equation: 1.5V = p_plus - p_minus = 0V - p_minus => p_minus = -1.5V.Therefore the potential of the minus pole is -1.5V.
Solution
Now the electric potential of the plus pole is also 10,000V. The potential of the minus pole must be 1.5V lower, so it must equal 9998.5V.This explanation is good indeed.
Sometimes you design a circuit where the main chip runs on +3.3V reference to the chips ground at 0V, but somewhere in the proces you end up with an extension board that wants 5V below the ground. For easy of use we just call this -5V instead of renaming everything to 0, 5, and 8,3V. Renaming also has the drawback that I like to measure everything reffering to the ground of the main chip. So I personally just don't rename and keep my reference there.
*fixed 8.5 typo to 8.3
Just so I understand.
In your example, let's say we have a power supply that distributes 5v and 8.5v.
The extension board is easy, we just hook it up from 5v to 0v.
For the 3.3v chip, are we wiring it between 8.5v and 5v? So it only sees a 3.3v voltage difference?
Correct.
A good 'at home' example is your computer power supply
Yes. That will give you a 3.5v difference.
Well, this is AI.
Well, this is correct.
Well, if they wanted an AI answer they would've asked an AI.