Actually did the Millikan Oil Drop and Coulomb's Law Today
If you were absent today:
1). We had a new seating order chosen with Skyward randomly and we only moved students who ended up in the same row to a different row (or tried to).
2). We handed out the new Physics Calendar for March
3). We handed out the E & M Research Assignment Due Friday March 15th. 1 Page Maximum!!!!
4). We explained the Millikan Oil Drop Experiment
I had the opportunity to do the Millikan Oil Drop Experiment as a Physics Major at UW-SP. I still remember going into a dark room every afternoon for a few weeks when it was beautiful weather outside and my friends were playing baseball. I remember spraying oil with an atomizer (so the drops would be charged negative) above a metal plate with a hole in it. Then I remember looking into a microscope that allowed me to see the individual oil drops falling toward a second metal plate. At first sight there were hundreds of drops but I had to control them until there was just one. How I would control the oil drops is I could flip a single throw switch and control the voltage on a power supply to cause the top plate to be charged positive (to attract the oil drops) and the bottom plate negative (to repel the negative oil drops). After I isolated one drop, I would adjust the voltage until I stopped the one oil drop in the middle of the plates. Then doing some Physics I could figure out a number. Next I repeated the process over and over and over and over again, hour after hour, day after day, week after week, until I had dozens of numbers that were all different. Now I figured out the largest number that was a factor of all my numbers and that was the charge on one oil drop. Example: Lets say the numbers were 480, 32, 6464, 4880, 2560, 964608, and 2048. All of these numbers are divisible by 16. Millikan obtained 1.6 X 10^-19 so since it was an electron he added a negative sign in front.
So if the quantity of charge on one electron is -1.6 X 10^-19 Coulombs/electron then what is the number of electrons in one coulomb of charge? Simply flip the above 1/x to get 6.25 X 10^18 electron/Coulomb
5. The cage of death
We made a cylindrical cage of chicken wire that a student (or several student crawled under and into) then zapped the metal cage with a tesla coil (that looked like lightning) (safe because low current). Since electrons repel each other and want to stay in the conductor it is perfectly safe in the Cage of Death (Faraday Cage). So in a lightning storm you need to stay in your metal car as it is a Faraday cage as is an airplane. It is not the rubber tires on the car (note the airplane is in the air, no rubber tires touching the ground) that protects you, it is the metal frame of the car. Note the following videos of Faraday Cages protecting people from dangerous voltages shooting plasma all over.