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| Negative voltage ? |
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| wertyu:
What is it , i can understand most electrical principals but negative voltage i cannot , is it like a negative pressure in a water analogy ? any links to videos or article that can explain it simply for me ? ill be reading all the stuff on here over time ! first timei joined a forum in years i thought they had gone extinct . thanks |
| rstofer:
It has to do with the reference point and I get to pick that point. Consider 2 batteries in series oriented left to right with the + output to the right. Suppose you put your DMM black wire on the junction between the batteries. Now probe the terminal on the right end and you will get some positive voltage. Probe the terminal on the left and you will get some negative voltage - relative to the center point 'ground'. Now move the black probe all the way to the left. If you test the center point with the red probe, you get a positive voltage and if you test the terminal on the right end you get a more positive voltage. So, what happened to that battery? Did it change in any way? No, only the reference point changed and I get to choose that point. ETA: Expand the experiment by putting the black probe on the right end of the stack. Now probe the center point and you will get some negative voltage. Probe the far left and you will get a more negative voltage. Voltage measurements are always relative to something. |
| IanMacdonald:
Electricity is a flow of the mobile electrons in a metal. Metals tend to be conductors because they consist of a lattice of atoms which loosely share their outer electrons, therefore it is relatively easy to persuade the electrons to move from atom to adjacent atom. Since electrons have a -ve charge they will tend to move towards any point which is more positive than their present potential. (Positive charges arise from the protons in the nuclei of atoms) An atom with an equal number of electrons and protons is neutral. One which lacks an electron or two has a net positive charge, and will attract electrons until that deficit is made up. The reverse if it has too many. The principle is really much the same as a fluid in a pipe, in that it's the difference in pressure between the pipe ends which determines the rate of flow. In fact, in the early days voltage was called pressure. The convention that electrons are 'negative' and protons 'positive' is just that, a convention. The reverse naming could equally well be used. |
| ebastler:
--- Quote from: wertyu on February 20, 2019, 03:55:07 pm ---What is it , i can understand most electrical principals but negative voltage i cannot , is it like a negative pressure in a water analogy ? --- End quote --- Yes, that is actually the right analogy. For those simple circuits which can be explained via the water/plumbing analogy, a negative voltage corresponds to negative water pressure. As explained by rstofer, it's all relative: ;) The proper "plumbing" analogy for a battery or other voltage source would be a pump with an input tube and an output tube, which maintains a constant pressure difference between the input and the output. Whether you call the input pressure "zero" and the output "positive", or call the output level "zero" and the input "negative", is a matter of definition. |
| wraper:
--- Quote from: ebastler on February 20, 2019, 04:15:16 pm --- --- Quote from: wertyu on February 20, 2019, 03:55:07 pm ---What is it , i can understand most electrical principals but negative voltage i cannot , is it like a negative pressure in a water analogy ? --- End quote --- Yes, that is actually the right analogy. For those simple circuits which can be explained via the water/plumbing analogy, a negative voltage corresponds to negative water pressure. As explained by rstofer, it's all relative: ;) The proper "plumbing" analogy for a battery or other voltage source would be a pump with an input tube and an output tube, which maintains a constant pressure difference between the input and the output. Whether you call the input pressure "zero" and the output "positive", or call the output level "zero" and the input "negative", is a matter of definition. --- End quote --- Actually it's not a proper analogy at all. Pressure cannot be negative, actual pressure does not go below zero, it's just pressure difference that produces force/flow in certain direction. On the other hand, both positively and negatively charged particles do exist and produce electric charge. And it's not necessarily electron flow that produces electric current. It can be positively charged particles as well. |
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