Faraday and Thomson figured out that all matter has some sort of definite quantity of electricity in it, and that it takes the same quantity of electricity to chemically decompose a substance as it does to keep it together. Then came Millikan, who is super-cool. I found a quote on wikipedia that shows just how super-cool:
"At the close of my sophomore year [...] my Greek professor [...] asked me to teach the course in elementary physics in the preparatory department during the next year. To my reply that I did not know any physics at all, his answer was, “Anyone who can do well in my Greek can teach physics.” “All right,” said I, “you will have to take the consequences, but I will try and see what I can do with it.” I at once purchased an Avery’s Elements of Physics, and spent the greater part of my summer vacation of 1889 at home … trying to master the subject. [...] I doubt if I have ever taught better in my life than in my first course in physics in 1889. I was so intensely interested in keeping my knowledge ahead of that of the class that they may have caught some of my own interest and enthusiasm."
How St. John's is THAT!? And although 1889 may seem like a while ago, he didn't die until 1953. Super modern. So, the reason I'm writing about Millikan and oil drops and electrons is because this experiment is worth writing about. The experiment is designed to find the absolute charge of electricity (i.e. the charge of a single electron) as well as to find the mass of the electron. Doing this requires a lot of math which I find pretty boring, but the apparatus and the concept behind it are very comprehensible. Here is a drawing of the apparatus. Sadly we didn't get to use thousands of volts yesterday...only a few hundred.
So those two plates, one above and the other below the field marked "uniform electric field" are electrically charged plates. Say the top one is charged positively and the bottom negatively. We spray teeny, tiny, oil drops into the large cannister on top and some of them float down through a hole and end up between the two charged plates. We can turn off the plates and the oil drops will float down really really slowly (about 15 seconds/2mm) because of the viscosity of the air, and then we can give the plates charge and the oil drops, depending on whether they were charged negatively or positively, will go up really fast or down really fast. If you measure the speed of the oil drops as they float down (at a constant rate) and as they shoot up (with one that is positively charged) you will notice that every once in a while they will change the speed at which they shoot up. This is evidence that the oil drop has "captured" an ion and picked up extra negative electric charge. The intervals between the speeds at which they shoot up provides evidence that electricity comes in discreet packets, electrons, and we can use our measurements to determine their charge and mass.
Anyway, this experiment means squinting into a microscope for hours on end flipping switches to make the oil drop go up and down while remaining in sight and timing with a stopwatch the times they take to go up and down. Sounds boring but is actually pretty exciting, especially since I got to use one of the set-ups that had a very small tv and camera instead of a microscope. I worked with Sarah Bern, a really nice Toronto-an I've just met (it's always exciting to make new friends at St. John's-one would think I would know everyone already) who was really fun to work with. After we collected all of our data we were supposed to begin doing the math to get the numbers we need for our lab report, but instead we just talked. It was a really nice college moment.
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