Well, this is AI.
Comment on What is negative voltage?
872XXE@feddit.org 5 days ago
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
EarWorm@lemmy.world 4 days ago
872XXE@feddit.org 4 days ago
Well, this is correct.
EarWorm@lemmy.world 4 days ago
Well, if they wanted an AI answer they would’ve asked an AI.
akunohana@piefed.blahaj.zone 5 days ago
Sic. This explanation is clear as day. Thanks!!!
JelleWho@lemmy.world 5 days ago
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 8,5V. 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.
CetaceanNeeded@lemmy.world 4 days ago
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?
JelleWho@lemmy.world 4 days ago
Correct.
A good ‘at home’ example is your computer power supply
TBi@lemmy.world 4 days ago
Yes. That will give you a 3.5v difference.
yetAnotherUser@discuss.tchncs.de 4 days ago
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.