Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electron speed

  1. Feb 26, 2010 #1
    My general science courses give various speeds for electrons to illustrate various examples. My preconception was that electrons always move very fast, but some of the examples from textbooks assume speeds that are a lot less than what I expected from an electron . Has the full range of possible speeds an electron can take been calculated or measured or both?
  2. jcsd
  3. Feb 26, 2010 #2


    Staff: Mentor

    An electron, like any massive particle, can go from 0 to just under c. In "everyday" situations like electrical circuits there are two important velocities, the Fermi speed which is the typical instantaneous speed due to thermal motion (~10^6 m/s) and the drift velocity which is the average speed corresponding to an electrical current (~10^-4 m/s).

  4. Feb 26, 2010 #3
    That's an awesome answer, thanks!
  5. Feb 26, 2010 #4


    Staff: Mentor

    You are very welcome!
  6. Feb 26, 2010 #5
    Experimental electron beam energies have ranged from fractions of an electron volt to ~50 GeV (at SLAC and the CERN 26-km-circumference LEP), Lorentz gammas up to ~100,000. One of the most beautiful electron-beam demonstrations I can remember is the undergraduate e/m Lorentz-force experiment, such as the 300-volt electron beam in a Helmholtz coil shown in this attachment.


    Every undergraduate physics lab must do this experiment,

    Bob S
  7. Feb 28, 2010 #6
    From the site you referred to:
    Perhaps its nitpicking but why do you think Fermi speed due to thermal motion? As far as I understand Fermi speed is there at 0K and alters only slightly at room temperature.
  8. Mar 1, 2010 #7
    The electron velocity in a standard CRT (cathode ray tube) TV set with a 10,000 volt electron gun is about 5.8 x 107 meters per second.

    Bob S
  9. Mar 1, 2010 #8
    The speed of light, because of zitterbewegung. :P
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook