How Did Millikan Determine The Number Of Oil Dropss

In the early 1900’s, Robert Millikan started studying the charge of an atom. He wanted to know whether there was a smallest unit of electric charge and if so, what is this charge and what is its magnitude in Coulombs. In order to test this he took small oil droplets and put them through an atomizer which ionized the oil droplets. He then placed the oil droplets in a closed system between two oppositely charged plates with the negatively charged plate on top. In order to figure out the value of ‘e’ (elementary charge) he had to find the electric force of the fields. To find the electrical force he suspended the oil droplet in the middle by making the electrical force equal to the gravitational force. Since he had already calculated the gravitational

Stoke’s law refers to drops that have roughly the same surface area as the volume. If the volume is greater than the surface area, the drops velocity would increase. If the surface area of the drop was greater than the volume, the drops velocity would decrease. Since he couldn’t control the size of the drops, he had to adjust his experiment by excluding the drops that did not fit within the size range of oil droplets that could be used for Stoke’s law. In other words, he had to use the oil drops that he believed had no extra variables affecting them. For example, if a drop was too small, it was rejected for inaccuracy because it was affected by Stoke’s law of viscosity in air. If a drop was too big, it would fall at a velocity too fast to record the time it took to drop accurately. In other words, Millikan was creating constant variables by disregarding these drops. Also Millikan had to regard some drops in the event that they possibly had dust particles on them. This would affect their weight which would increase the gravitational force which also increases the velocity at which they fall. Therefore, he would have an inaccurate measurement for the velocity of the oil