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The experiment that proved electrons to compose current

  1. Apr 26, 2008 #1
    I remember reading somewhere that it was discovered that electrons, not protons, composed current when an accelerated conductor was found to have slightly negative charge on the end opposite the direction of the acceleration. Because of this it was determined that electrons were free to move in conductors, not protons, and electrons were what composed current.

    I can't find the name of this experiment, does anyone remember?
  2. jcsd
  3. Apr 27, 2008 #2
    Never heard of it. I think the properties of cathode rays (electrons) seems to have determined that charge carriers were negatively charged.
  4. Apr 27, 2008 #3


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    The Hall effect shows that the current carriers are negative.
  5. Apr 27, 2008 #4
    True and true, but I managed to find the text I was looking for, and it was called the Tolman-Stewart experiment. From Knight's "Physics for Scientists and Engineers, Volume 4":

    "The Tolman-Stewart experiment of 1916 was the first direct evidence that electrons are the charge carriers in metals. Tolman and Stewart caused a metal rod to accelerate very rapidly. The inertia of the charge carriers within the metal (and Newton's first law) causes them to be "thrown" to the rear surface of the metal rod as it accelerates away...Tolman and Stewart found that the rear surface of a metal rod becomes negatively charged as it accelerates."
  6. Apr 27, 2008 #5
    Cool, hbweb. I wonder how a P-type semiconductor would measure.
  7. Apr 27, 2008 #6
    I don't know much about p-type semiconductors, but from what I have read a positive "hole" is created when an electron is accepted by the impurity. If all of the electrons are shoved to the back of the rod when it is accelerated, then all of the positive holes should be created back there, and thus the end should test positive...

    I guess it was for the better that Tolman and Stewart didn't use a p-type when they did their test.
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