The Millikan oil drop experiment is a famous physics experiment conducted by American scientist Robert A. Millikan in 1909 to determine the fundamental unit of electric charge, known as the electron. This experiment involved observing the motion of tiny oil droplets in an electric field to measure the charge on individual electrons.
In the experiment, a fine mist of oil droplets was sprayed into a chamber where they were subjected to an electric field. By measuring the droplets' motion and the strength of the electric field, Millikan was able to calculate the charge on each droplet. This allowed him to determine that the charge on each droplet was a multiple of the fundamental unit of electric charge, which is now known as the electron charge.
The potential difference, or voltage, is the key factor in the Millikan oil drop experiment. It is created by applying an electric field between two parallel plates, causing the oil droplets to experience either an upward or downward force depending on their charge. By varying the potential difference, Millikan was able to measure the charge on each droplet and determine the value of the electron charge.
The Millikan oil drop experiment was a crucial step in the development of modern atomic theory. By accurately measuring the charge of individual electrons, Millikan provided evidence for the existence of discrete, indivisible particles within the atom. This experiment also helped to confirm the structure of the atom proposed by J.J. Thomson, with a positively charged nucleus surrounded by negatively charged electrons.
While the Millikan oil drop experiment was groundbreaking in its time, it is not without its limitations. The accuracy of the experiment relies heavily on the assumption that the oil droplets have a perfectly spherical shape, which may not always be the case. Additionally, the experiment does not take into account any other particles within the atom, such as protons and neutrons, which were not yet discovered at the time. However, despite these limitations, the Millikan oil drop experiment remains a crucial milestone in the history of atomic theory.