The principle of Millikan's experiment is:
1. He found the value of charge attached to the oil drop. He repeated the expt many many times and found that the charge is a multiple of a common factor e, the basic electronic charge with a value of 1.6*-19 C.
The simplest form of this expt is ,
* Hold the oil drop stationary inside the parallel plate by adjusting the voltage between the plates.
* Switch off the electric field and measure the terminal velocity of the same oil drop that was held stationary earlier.
Two equations can be written: mg = drag force and mg = qE. and a third equation that is also considered is mass of oil drop is m = densityxvolume of sphere(oildrop). Put this three equations together , q can be calculated.
The upthrust can be considered if you want to be more accurate in your calculation of q. For understanding in general it can be ignored as it is a minor correction to readings of q.
Trythis. Play with oil drops applet. Figure it out.
