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An optical levitation system for a physics teaching laboratory

Journal article
Authors Oscar Isaksson
M. Karlsteen
Mats Rostedt
Dag Hanstorp
Published in American Journal of Physics
Volume 86
Issue 2
Pages 135-142
ISSN 0002-9505
Publication year 2018
Published at Department of Physics (GU)
Pages 135-142
Language en
Links doi.org/10.1119/1.5007738
Keywords oil-drop experiment, radiation pressure, particles, tweezers, trap, Education & Educational Research, Physics
Subject categories Physical Sciences

Abstract

We describe an experimental system based on optical levitation of an oil droplet. When combined with an applied electric field and a source of ionizing radiation, the setup permits the investigation of physical phenomena such as radiation pressure, light diffraction, the motion of a charged particle in an oscillating electric field, and the interaction of ionizing radiation with matter. The trapping occurs by creating an equilibrium between a radiation pressure force and the force of gravity. We have found that an oil droplet can be trapped for at least nine hours. The system can be used to measure the size and total electric charge on the trapped droplet. The intensity of the light from the trapping laser that is scattered by the droplet is sufficient to allow the droplet to be easily seen with the naked eye, covered by laser alignment goggles. When oscillating under the influence of an ac electric field, the motion of the droplet can be described as that of a driven, damped harmonic oscillator. The magnitude and polarity of the charge can be altered by exposing the droplet to ionizing radiation from a low-activity radioactive source. Our goal was to design a hands-on setup that allows undergraduate and graduate students to observe and better understand fundamental physical processes. (C) 2018 American Association of Physics Teachers.

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