milikin oil drop experiment British physicist JJ Thompson had measured the ratio of electrical charge to the mass of an electron using a cathode ray tube in 1897 later ra milikin looked to determine the charge on the electrons the famous method that he devised between 1906 and 1914 to measure the charge e of an electron is known as the milikin oil drop experiment using this method he calculated that the charge on an electron was about 1.6 * 1019 kums in the milikin oil drop method an atomizer produces oil droplets in the form of mist which are sent through a plate of electrical condenser there are different forces which act on the oil drop including gravitational electrostatic force due to electric field and viscous drag Force the rate at which these Drops Fall were measured by observing them through a micrometer eye piece of a telescope X-rays were passed through the chamber to ionize the air inside on colliding with gaseous ions these oil droplets acquire charge the rate at which these droplets fall can be controlled by changing the strength of Applied voltage to the plate with this experiment he observed that the magnitude of electrical charge Q on the droplets is always a multiple of electrical charge e that is Q is equal to NE e where n is equal to 1 2 3 and so on using the value of charge of the electron the mass of the electron me was then determined by combining Thompson's value of e By Me ratio the value shown is the value of the mass of an electron