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| how exactly resistor works |
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| iMo:
There is not such thing like electrons flowing through the pipes/wires generating the heat. The electrons are tiny and pretty week, and their speed is a few centimeters per second in the metal. The heat is created by fields, spanning over the whole Universe.. Weird.. |
| T3sl4co1l:
Just to emphasize: Energy is not power. Energy over time is power. Energy is more of a one-time thing. A resistor is more of a continuous thing. When you apply voltage and current to a resistor, you dissipate power. The dissipated energy counts up over time. Most precisely, energy is the integral of power with respect to time, or likewise power is the time derivative of energy. (If you've not had calculus, this probably doesn't help. On the upside, if you've had Newtonian mechanics, you will know this distinction. Energy is what it takes to get a car moving; power is what it takes to keep a car moving against wind resistance and such.) Tim |
| djacobow:
--- Quote from: rstofer on September 28, 2018, 03:53:07 pm ---I'm not a huge fan of the water analogy beyond about 10 minutes the first day of class. We have Ohm's Law and that tells us all we need to know about the relationship between voltage, current and resistance. It's a Law, not a suggestion! --- End quote --- But it's not a law at all. It describes a common - but not universal - material property: that voltage is proportional to voltage by a fixed constant. But even where it is essentially true, such as in a carbon resistor or in a metal, I believe it is not 100% completely true. There are nonlinear factors. But we mortals really like to linearize things because it makes life much easier. And so we end up doing E=IR everywhere, even in transistor circuits for the "small" signal, because it's convenient - but it ain't right. |
| hamster_nz:
--- Quote from: macboy on September 28, 2018, 01:54:42 pm --- --- Quote from: hamster_nz on September 28, 2018, 11:51:42 am --- --- Quote from: rs20 on September 28, 2018, 11:15:34 am ---Just to perfectly clarify what glarsson is correctly pointing out; --- Quote from: tester43 on September 28, 2018, 10:41:09 am ---a narrow tube between two large tubes limiting the water flow (no wasted energy). --- End quote --- The "no wasted energy" part is wrong. A narrow tube does dissipate energy. --- End quote --- Can you explain this to me a little more? I can't resolve this in my head. Unless the pipe is tapered (e.g. a nozzle) the same mass of fluid that enters the pipe exits the pipe, traveling at the same speed, so it is carrying the same energy, regardless of the diameter of the pipe. ... --- End quote --- Is the pressure the same on both sides of the pipe? If not, what does this imply? Does the hydraulic pump need to work harder to push a specific flow rate through a narrow pipe or a large one? So if the pump needs to output more energy into the narrow pipe system, where does it go? Your hydraulic pressure is analogous to electrical voltage. The flow rate is analogous to electrical current. --- End quote --- Humm.... but what is the mechanism in the fluid that converts the power supplied by the pump into heat? It is altered by the viscosity of the fluid, and I guess you get the same heating effect (to different extents) in lubricating oils, maple syrup or thick tar. It only happens when they sheer or flow, so I guess it must be something like friction within the fluid itself. Time to get lost in Wikipedia on Fluid Mechanics (and most likely ending up reading about the design of Roman Sandals, via aqueducts and flume bridges) , I guess... |
| Brumby:
--- Quote from: djacobow on September 29, 2018, 03:40:16 am ---But it's not a law at all. It describes a common - but not universal - material property: that voltage is proportional to voltage by a fixed constant. But even where it is essentially true, such as in a carbon resistor or in a metal, I believe it is not 100% completely true. There are nonlinear factors. --- End quote --- Incorrect. Quite incorrect, in fact. Ohm's Law is a law - even in the strictest sense. Nobody has said that resistance is constant, which would appear to be the premise of your statement. We know about temperature coefficients and other factors that can affect the resistance of a component under specific conditions - but, under those conditions Ohm's Law is entirely consistent. |
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