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| This electons flowing rubbish |
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| Terry Bites:
Why do people just keep on promoting bad science? Electrons do not flow in conductors or semiconductors or anything else when a current is flowing. Yeah Yeah drift current... diffusion current... blah. Charge is transported around the current path under the influence of the applied voltage. Let's stamp out the BS in EE! |
| TimFox:
There are exceptions to your absolute statement. For example, electrons do flow from a hot cathode to the anode under "saturated" condition (not limited by space charge), with the resulting shot noise in the current in the rest of the circuit. (Space charge modifies the equations, but the flow to the anode is still a host of electrons at a reasonable velocity.) Usually in the first chapter about "current" in an undergraduate physics textbook on electromagnetism there will be a list of examples of different physical situations where there is current flow, including the vacuum diode above. |
| T3sl4co1l:
I suppose it's tricky. A hydraulic analogy is quite productive. There, too, the drift and particle velocities are widely disparate; perhaps one should be careful to emphasize the relevance of the speed of sound (mean velocity of molecules) in that case, and show the analogy with electron drift. But it's also hard to motivate that; you can't splash some water around and say that it happened at the speed of sound, no, it's much too fast to see. It's easily illustrated with resonators and frequency or step response, but those require much more knowledge (dynamics, wave mechanics) to understand. Worst of all, electron waves flow at the speed of light in the medium, not at the thermal velocity, so the analogy again breaks down, in a different way. And neither case seems to be good preparation for the student, for the truth that alternating current flows largely in the space between conductors, rather than in them (in the bulk) as such. Tim |
| IanB:
--- Quote from: Terry Bites on March 01, 2021, 02:24:14 pm ---Charge is transported around the current path under the influence of the applied voltage. --- End quote --- So I'm slightly curious. How is charge transported around the current path without mobile charge carriers? |
| TimFox:
In simplistic terms, I like to think of current flow through a normal solid conductor as a slight tendency of a zillion electrons to move to the right under the influence of the potential difference from left to right, superimposed on their random thermal motion that exists even without applied voltage. |
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