Timeline for What is negative voltage?
Current License: CC BY-SA 2.5
7 events
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| Apr 17, 2013 at 19:04 | comment | added | Eryk Sun | @supercat: My comment was about how the change in electrical potential (V) works for both positive and negative charges (coulombs). If you place a positive charge q at the 5V side, it accelerates to the 3V side (say it's in vacuum). It's kinetic energy increases and potential energy (U) decreases. It makes sense that the dV is -2V since dU = q * dV. A negative charge -q set at the 3V position accelerates to the 5V position. Again the potential energy has to decrease. The dV is +2V, which makes sense because dU = -q * dV. | |
| Apr 17, 2013 at 15:57 | comment | added | supercat | @eryksun: While it's true that potential energy is measured by taking zero at infinity, if one thinks in terms of height (a more familiar concept, and the original one above), one could recognize that while one could define absolute altitude (distance to the Earth's center of mass), it is in most contexts more helpful to define elevation relative to something that's a little closer [e.g. the "natural" height of the terrain]. If e.g. a house is built in a flat area, one may describe the floor of the basement as having an elevation of -2 meters relative to the surrounding terrain. | |
| Feb 27, 2011 at 13:06 | comment | added | Eryk Sun | Gravitational potential energy is referenced negative by setting it to zero at infinity. Electrical potential energy is negative between two charges of opposite sign and positive between charges of the same sign. Say there's an electrical potential drop from 5V to 3V. A positive test charge q would add -2q to its potential energy (becoming less positive), while a negative test charge -q would accelerate in the other direction (+2V, from 3V to 5V), but also adding -2q to its potential energy (becoming more negative). In both cases potential energy decreases. | |
| Feb 17, 2011 at 23:30 | comment | added | pingswept | Good points, the both of you. | |
| Feb 17, 2011 at 23:11 | comment | added | Kortuk | @michaelStum, @pingswept, I always like to remind people that there is potential energy from height if you take physics. (mgh) is potential energy, if I pick the atmosphere as my reference we all suddenly have negative potential energy. | |
| Feb 17, 2011 at 15:16 | comment | added | endolith | Ground is just a convention, too. You can pick any single point in a circuit and label it ground, but we choose specific points out of convention. | |
| Feb 17, 2011 at 4:00 | history | answered | pingswept | CC BY-SA 2.5 |