Millikan's oil drop experiment
A brief summary of what happened before Millikan's experiment
Electrons where quite a mystery in the 19th century. Not only where there nature unknown whether they are a particle or a wave(they are both) but whether it is a component of atoms or not. in the 19th century it was noticed by William Crooke that when two opposite electrodes have high voltage the glass surrounding it glowed. Then later J.J Thomoson conducted multiple experiments on ray(which was named cathode ray) are negatively charged particle. In addition he also reached the conclusion that the electrons are a part of atoms and managed to find the charge to mass by equating the centripetal force and magnetic force acting on the electron during the experiment.
| After that Robert Andrews Millikan did an experiment to find the charge of the electron and mass of the electron the experiment goes as follows: | https://ipfs.busy.org/ipfs/QmfHJ8ZxCsAjabj4xmJwwLKzUvG8ZJVisSNCNEwf54zUJb |
Robert Millikan used an apparatus which have sprays of oil drops falling through a hole. Where the oil drop falls through two pairs of metals that have a potential difference across and an insulator ring to disable the two metals plates to get on contact then there are 4 holes for a microscope and illuminating light.
After running the experiment once as the base of the experiment the oil drops is then ionized through cathode rays (x rays), and the charges where stronger by increasing the voltage, which can affect the oil’s fall by slowing it down stopping it or even letting it raise. Then the charge can be calculated by calculating the upwards force that act as an opposite force to gravity.
When the experiment is ran first the drag force for the drop by Stoke’s law then the weight is calculated by getting the volume of the oil drop and multiplying it with the density and acceleration (gravity). Then the voltage is turned on and electric force is measured by that the charge of the electron can be calculated as all of the charges are all multiples of a small value which is equal to 1.6*10^-19 coulombs.