Millikan Experiment: How an electron's mass was discovered
The Noprah Show
Noprah: Good evening! Today we have a special guest here with us: The Magnificent Mr. Millikan, who is responsible for finding out the mass and charge of an electron!
Millikan: Why hello there, Noprah. It's about time my work is finally getting the recognition it deserves.*(see note)
N: Definitely! I'd like to know more about it. Why did you experiment?
M: Well, I've always been interested in science, and it really struck me that the actual mass and charge of an electron was unknown. Of course, we know the ratio thanks to my dear friend J.J. Thomson, but I reasoned that we would need the mass of electrons to further science. Ah, that man was on the right track to figuring it out, but alas, the poor soul used water vapor in his experiments, which evaporates too quickly. I, having abundant resources, used oil droplets instead.
N: You're quite the genius! What did you do with the oil droplets?
Millikan: Why hello there, Noprah. It's about time my work is finally getting the recognition it deserves.*(see note)
N: Definitely! I'd like to know more about it. Why did you experiment?
M: Well, I've always been interested in science, and it really struck me that the actual mass and charge of an electron was unknown. Of course, we know the ratio thanks to my dear friend J.J. Thomson, but I reasoned that we would need the mass of electrons to further science. Ah, that man was on the right track to figuring it out, but alas, the poor soul used water vapor in his experiments, which evaporates too quickly. I, having abundant resources, used oil droplets instead.
N: You're quite the genius! What did you do with the oil droplets?
M: I suspended very small oil droplets between two electrodes that were parallel to each other. If you refer to my diagram, when the droplet passed the first electrode, it entered a chamber where it could be suspended or even moved upwards when I turned on voltage from x-rays. I could measure how much voltage I had to use to suspend an individual droplet.
N: How was this information helpful? M: Ah, well you see, since we already know the mass and density of the droplets, once we determine the charge needed to counteract gravity and suspend the droplet, we could find out the charge of oil droplets. I did this many, many, many times, and the numbers kept coming up as multiples of this number: 1.5924(17)×10−19 (Coulombs). I took this to be the charge of a single electron. |
N: Incredible! I can't believe you did this all by yourself!
M: Hehehe...about that...well I gotta go, thanks for having me!
*It is known now that Millikan actually worked with a partner, Harvey Fletcher, an undergraduate student at University of Chicago. Neither of them publicly recognized this even at Fletcher's death, despite the fact that Millikan won the 1923 Nobel Prize for Physics for his (?) work.
M: Hehehe...about that...well I gotta go, thanks for having me!
*It is known now that Millikan actually worked with a partner, Harvey Fletcher, an undergraduate student at University of Chicago. Neither of them publicly recognized this even at Fletcher's death, despite the fact that Millikan won the 1923 Nobel Prize for Physics for his (?) work.