The experiment that proved electrons to compose current

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Discussion Overview

The discussion revolves around the historical experiment that demonstrated electrons as the charge carriers in electric current, specifically referencing the Tolman-Stewart experiment. Participants explore the implications of this finding and its relation to different types of semiconductors.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant recalls that the discovery of electrons as charge carriers was linked to an experiment where an accelerated conductor exhibited a negative charge at one end, suggesting that electrons, not protons, compose current.
  • Another participant suggests that the properties of cathode rays indicated that charge carriers are negatively charged, implying a historical basis for identifying electrons as the carriers.
  • The Hall effect is mentioned as evidence that current carriers are negative, contributing to the understanding of charge in conductors.
  • A participant identifies the Tolman-Stewart experiment as the source of direct evidence for electrons as charge carriers, describing how the experiment involved accelerating a metal rod and observing the resulting charge distribution.
  • One participant expresses curiosity about how a P-type semiconductor would behave in a similar experiment, questioning the implications of charge carriers in such materials.
  • Another participant speculates that if electrons are displaced to the back of the rod during acceleration, positive holes would be created at that end, leading to a positive charge measurement, and reflects on the choice of materials in the original experiment.

Areas of Agreement / Disagreement

Participants generally agree on the identification of electrons as charge carriers based on the Tolman-Stewart experiment and related concepts, but there is uncertainty regarding the behavior of P-type semiconductors and how they would measure in similar conditions.

Contextual Notes

Some assumptions about the behavior of charge carriers in different materials remain unresolved, particularly concerning the dynamics of P-type semiconductors in the context of acceleration and charge distribution.

hbweb500
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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?
 
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Never heard of it. I think the properties of cathode rays (electrons) seems to have determined that charge carriers were negatively charged.
 
The Hall effect shows that the current carriers are negative.
 
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."
 
Cool, hbweb. I wonder how a P-type semiconductor would measure.
 
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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