This is a "loaded" question. (http://en.wikipedia.org/wiki/Loaded_question)Revered Members,
The drift velocity is of the order 0.1 cm/s. If the drift velocity is of such small magnitude, how conductors maintain a continuous flow of electrons?
This is actually incorrect. If the electrons are locked down the material / element is an insulator, but with metals the outer electrons float, they move where they wish easily, usually in a random fashion. This is what makes them a conductor, the presence of an electric field make them drift in a specific direction. If you start talking about individual atoms it becomes more true, but metals usually have a structure, be it crystal or other. Ever look at metals under high power they are granular.I've always found the marbles-in-a-tube analogy to be misleading. Think about it: the metal in wire is neutrally charged. For every electron pushing you from behind there's a proton nearby pulling you back just as hard.
Maybe I'm mis-reading this, but this is backwards. Excess charge in a conductor will apply a coulomb force (unscreened because the charges aren't balanced) which will cause the mobile charges to redistribute in such a way that the excess immediately migrates to the surface.With a conductor a charge (excess electrons or minimum electrons) still distribute themselves evenly through out the material because of the electron mobility.
You are correct.Maybe I'm mis-reading this, but this is backwards. Excess charge in a conductor will apply a coulomb force (unscreened because the charges aren't balanced) which will cause the mobile charges to redistribute in such a way that the excess immediately migrates to the surface.
Quote from the Chabay and Sherwood textbook I referenced: "...any excess charge on a piece of metal, or any conductor, are always found on an outer or inner surface."
If I've been taught by crappy sources, please let me know ASAP.
Sure, those internal charge regions show the flow of energy (seen as heat in a resistor) into the material instead of space at those points. It also shows that energy/charge moves (like a lightwave) from both ends of the battery into the load while the charge carriers (slowly) circulate round.That's a cool document. It does illustrate, however, that conductors can contain interior excess charge in regions where bulk resistivity is changing (such as at the ends of a resistor) in the non-equilibrium case of flowing charge.
http://en.wikipedia.org/wiki/Electron_mobility#Temperature_dependence_of_mobilityLattice (phonon) scattering
At any temperature above absolute zero, the vibrating atoms create pressure (acoustic) waves in the crystal, which are termed phonons. Like electrons, phonons can be considered to be particles. A phonon can interact (collide) with an electron (or hole) and scatter it. At higher temperature, there are more phonons, therefore increased phonon scattering which tends to reduce mobility.
Professor Lewin's lecture on Ohms law helps give you an idea about this. In a nutshell, a simple classical model shows conductivity is proportial to the time between collisions. High temperature implies shorter time between collisions and lower conductivity.As we all know resistivity & hence resistance, in metals GENERALLY increases with temperature. This has always seemed odd to me considering that the electrons in the outer orbits are in a more excited state and should be more mobile with increasing temperature.
Any ideas anyone?
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by Jake Hertz
by Jake Hertz