Millikan: Good to the Last (Oil) Drop

Earl F. Pearson
Department of Chemistry, Middle Tennessee State University, Murfreesboro, TN 30132
J. Chem. Educ., 2006, 83 (9), p 1312A
DOI: 10.1021/ed083p1312A
Publication Date (Web): September 1, 2006

Abstract

Michael Faraday's experiments with electrolysis had shown that there were tiny units of electric charge that could not be divided into smaller charges. Robert Millikan confirmed this and found a way to measure the quantity of charge on an electron. Millikan used charged droplets of oil sprayed from an atomizer. An oil droplet could be negatively charged (excess electrons), positively charged (deficiency of electrons), or uncharged. This Activity uses a procedure analogous to Millikan's. In this analogy, drop-shaped pieces of magnet represent oil drops, steel BBs represent the electrons, and the mass of a BB represents the charge of an electron. BB samples are composed of individual BBs just as the charge that resides on oil drops consists of individual electrons. The smallest possible difference in mass between any two samples of BBs should be the mass of a single BB just as the smallest difference in charge between any two oil drops was the charge of a single electron.

Keywords (Audience):

First-Year Undergraduate / General

Keywords (Domain):

Demonstrations

Keywords (Feature):

JCE Classroom Activity

Keywords (Pedagogy):

Analogies / Transfer

Keywords (Subject):

Atomic Properties / Structure
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History

  • Received: August 03, 2009

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