1st Student's Major

Physics and Astronomy

1st Student's College

Science, Engineering and Technology

Students' Professional Biography

Eric Ehler is a graduate of the physics department at Minnesota State University, Mankato. He will be attending Medical School in the University of Wisconsin’s Medical Physics program with a full Research Assistantship. His initial research will be in the fMRI (functional MRI) research group at the University of Wisconsin. Aaron Hanson is currently a senior at Minnesota State University, Mankato. He will graduate in Fall 2005 with degrees in math and physics. He plans on going to graduate school for physics upon graduation from MSU.

Mentor's Name

Mark Pickar

Mentor's Email Address


Mentor's Department

Physics and Astronomy

Mentor's College

Science, Engineering and Technology


Brownian motion has a significant effect on small particles suspended in a fluid. Since the Millikan oil drop experiment involves measuring the rise and fall velocities of very small oil drops suspended in air, it stands to reason that the motion of these drops will be affected by collisions with particles of air. The result of this is that the measured rise and fall velocities of each drop will not be the same as if these drops were suspended in vacuum. The size of the effect of Brownian motion is related to the mass and the radius of the oil drop, and is also related to the temperature of the surrounding fluid. In our experiment, we calculated the charge of multiple drops of varying size. The charge on each was first calculated without considering Brownian motion, and then was calculated again while taking Brownian motion into account. When Brownian motion was taken into consideration, the accuracy of our calculation of the fundamental charge of an electron improved by a factor of six, permitting a determination of the value of the fundamental unit of electric charge (the charge of an electron) that differed from the accepted value by less than 1%. The effect of Brownian motion in the classic Millikan oil drop experiment is significant enough to be observed with basic undergraduate apparatus if sufficient precision is attained by careful measurement.

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

Included in

Physics Commons



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