3 ms·

How can you make sure you don't end up with 2e as a result? (Or any other multiple)

Terr_ 2y ago
In 1909 the results results were couched in some "elementary electric charge" quantity, since the now-familiar subatomic particle model (and the "electron") was still gaining acceptance. I expect that the greater the number of trials, it becomes easier it is to detect a distinction between closer-multiples, and if at some point more trials stops changing the answer then you've likely converged on e, unless there's some new principle like "X-ray exposure only affects charge in in multiples of e greater than one."
- adrian_b 2y ago
  The approximate value of the elementary electric charge had been known since 1874, when it was first computed by George Johnstone Stoney. After Stoney, other experiments had reduced the uncertainty with which the value was known, but it remained relatively high. The importance of the experiments of Robert Andrews Millikan consists in the fact that the uncertainty of the value of the elementary electric charge obtained by this method was much smaller than by any previous method (he claimed that it was better than one half of one percent, but he used wrong values for the viscosity of air, so his actual result was off by more than that, but still by less than one percent from the correct result).
dekhn 2y ago
He did- he selected the lowest value, ignoring all the multiples.
- ceejayoz 2y ago
  Not ignoring the multiples; the multiples verify the result. If you calculate the charge of one at 1e and you measure 2.5e, something went wrong. All values must be a multiple of the lowest.
nkmnz 2y ago
You do. Thae size of the steps between the results is the “quantum” of a single transferable charge.
SyzygyRhythm 2y ago
For that to happen, you would have to be very unlucky: all of your measurements would have to be 2e, 4e, 6e, etc. If a 3e or 5e sneaked in there, you'd realize that the charge was e, not 2e. With enough measurements, you can be confident that you've hit all the expected multiples of the quantum.
- db48x 2y ago
  Not quite so. They did end up measuring a multiple of the fundamental electric charge. The experiment really measured 3e, 6e, 9e, etc. It turns out that the electron and proton have an electric charge 3× bigger than that of a quark. Since the experiment didn’t generate any free quarks, nobody noticed for years. Even today the mistake persists and school children are taught, unironically, that down quarks have ±⅓ of the fundamental indivisible unit of electric charge and that up quarks have ±⅔e.
  - wholinator2 2y ago
    No need to nitpick, the original comment states perfectly accurately that he was measuring the fundamental charge _of the electron_, from which the constant e is derived. We've been using e to mean _electron_ charge for a very long time. Where do you get the idea that constant has anything to do with quarks?
    - db48x 2y ago
      https://i.kym-cdn.com/photos/images/original/000/992/402/c35.gif https://i.kym-cdn.com/photos/images/original/000/992/402/c35... But seriously, it really is time to fix all the chemistry textbooks so that the charge of the electron is +3 instead of −1.
      - empyrrhicist 2y ago
        Why, to make all that quark chemistry a bit easier?
        2y ago

In 1909 the results results were couched in some "elementary electric charge" quantity, since the now-familiar subatomic particle model (and the "electron") was still gaining acceptance. I expect that the greater the number of trials, it becomes easier it is to detect a distinction between closer-multiples, and if at some point more trials stops changing the answer then you've likely converged on e, unless there's some new principle like "X-ray exposure only affects charge in in multiples of e greater than one."

adrian_b 2y ago
The approximate value of the elementary electric charge had been known since 1874, when it was first computed by George Johnstone Stoney. After Stoney, other experiments had reduced the uncertainty with which the value was known, but it remained relatively high. The importance of the experiments of Robert Andrews Millikan consists in the fact that the uncertainty of the value of the elementary electric charge obtained by this method was much smaller than by any previous method (he claimed that it was better than one half of one percent, but he used wrong values for the viscosity of air, so his actual result was off by more than that, but still by less than one percent from the correct result).

dekhn 2y ago

He did- he selected the lowest value, ignoring all the multiples.

ceejayoz 2y ago
Not ignoring the multiples; the multiples verify the result. If you calculate the charge of one at 1e and you measure 2.5e, something went wrong. All values must be a multiple of the lowest.

nkmnz 2y ago

You do. Thae size of the steps between the results is the “quantum” of a single transferable charge.

SyzygyRhythm 2y ago

For that to happen, you would have to be very unlucky: all of your measurements would have to be 2e, 4e, 6e, etc. If a 3e or 5e sneaked in there, you'd realize that the charge was e, not 2e. With enough measurements, you can be confident that you've hit all the expected multiples of the quantum.

db48x 2y ago
Not quite so. They did end up measuring a multiple of the fundamental electric charge. The experiment really measured 3e, 6e, 9e, etc. It turns out that the electron and proton have an electric charge 3× bigger than that of a quark. Since the experiment didn’t generate any free quarks, nobody noticed for years. Even today the mistake persists and school children are taught, unironically, that down quarks have ±⅓ of the fundamental indivisible unit of electric charge and that up quarks have ±⅔e.
- wholinator2 2y ago
  No need to nitpick, the original comment states perfectly accurately that he was measuring the fundamental charge _of the electron_, from which the constant e is derived. We've been using e to mean _electron_ charge for a very long time. Where do you get the idea that constant has anything to do with quarks?
  - db48x 2y ago
    https://i.kym-cdn.com/photos/images/original/000/992/402/c35.gif https://i.kym-cdn.com/photos/images/original/000/992/402/c35... But seriously, it really is time to fix all the chemistry textbooks so that the charge of the electron is +3 instead of −1.
    - empyrrhicist 2y ago
      Why, to make all that quark chemistry a bit easier?
      - 2y ago