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Millikan's Oil Drop
Experiment

Authors: Ms. Giselle dos Santos Castro - Federal University of Ceara - UFC
Dr. Nildo Loiola Dias - Federal University of Ceara - UFC

CONTROLS:

- Click on NEW DROPLET and then SPRAY to generate a droplet. With this, a droplet enters the space between the capacitor plates through an upper opening and falls by gravity and electrical attraction. The droplet descent velocity is shown with a minus sign. The droplet will have positive velocity when rising.
- The droplet velocity can be changed by varying the Potential via the slider.
- The Switch reverses the charges on the capacitor and thus modifies the direction of the electrical force on the droplet.

DESCRIPTION OF THE SIMULATION:

In Millikan's experiment, oil droplets produced by a sprayer are launched into a region where there is an electric field that is produced by applying an electric potential difference between the parallel plates of a capacitor. Some dropletes thus formed are electrically charged, therefore, subject to the action of the electric field. In reality, each electrically charged droplet is affected by four forces: the weight force (Fg), the electrical force (FE), the viscous (frictional) force on air (FV), and the buoyant force (FB). In this simulation droplets of silicone oil are generated electrically charged with a random number of electrons and with randomly generated volumes. The potential difference between the capacitor plates can be regulated using a slider. The simulation provides the descent and ascent velocity of the oil droplet. Data analysis (velocity of rise and fall of the same drop, potential difference between the capacitor plates and some constants) allows the determination of the charge of each droplet. Analysis of the data from several droplets allows the determination of the elementary charge.

For an analysis of the data, consult one of the proposed ACTIVITY GUIDE.

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