6A42.20 - Refraction - Laser and Tank

Code Number:
Demo Title:
Refraction - Laser and Tank
Refraction of Light Waves
Area of Study:
Fish Tank with Water, Fluorescein Dye (Water Soluble), Helium-Neon Laser (5 mW), Green Laser Pointers, Pine-Sol, and Green Fluorescent Dye.

Video Credit: Jonathan M. Sullivan-Wood

Using the laser you may demonstrate total internal reflection and by using the aerosol haze spray or water mist to make the laser beam visible in air you may demonstrate index of refraction properties.

CAUTION: These are high power lasers.  Extreme care must be taken to insure that they are NEVER pointed at the audience, or more likely, impact the eyes of the lecturer.

The usual solution for the fish tank is to put 2 tablespoons of "Pine-Sol" into the 40 gallons of water that the tank holds.  1/4 bottle of the green fluorescent dye can also be added to enhance the laser beam viewing.  This solution will work with both green and red lasers.

A solution that will work only for red lasers is to put 3 to 4 teaspoons of water soluble Fluorescein into the 40 gallons of water the tank holds.

The above solutions will only need to be emptied from the tank if the water become dirty of collects too much chalk.  Otherwise, they will remain good for this demonstration for up to a decade.

  • Ana Gostincar Blagotinsek, "Visualizing Vision", TPT, Vol. 61, #1, Jan. 2023, p. 55.
  • Thomas B. Greenslade Jr., "Reviving the Gilley Board: Measuring the Index of Refraction of Water", TPT, Vol. 59, #1, Jan. 2021, p. 60.
  • Santiago Velasco and Alejandro del Mazo, "Visualization of Four Optics Phenomena in a Single Experiment", TPT, Vol. 57, #6, Sept. 2019, p. 430.
  • Gonzalo Fuster, Roberto Rojas, and Viktor Slüsarenko, "Color Fringes Bordering Black Stripes at the Bottom of a Swimming Pool", TPT, Vol. 54, #6, Sept. 2016, p. 354.
  • James Metz, "The Geometry of Snell's Law", TPT, Vol. 52, #3, Mar. 2014, p. 177.
  • Christian T. Corrao, "The Physicist Fish", TPT, Vol. 48, #7, Oct. 2010, p. 491.
  • Paul Hewitt, "Figuring Physics: Light Rays", TPT, Vol. 39, #6, Sept. 2001, p. 332.
  • Ronald Newburgh, Wolfgang Rueckner, Joseph Peidle, and Douglass Goodale, "Using the Small-Angle Approximation to Measure the Index of Refraction of Water", TPT, Vol. 38, #8, Nov. 2000, p. 478.
  • Alfred F. Leung, Simon George, and Karl C. Mamola, "Simple Homemade Container for Measuring Refractive Index", TPT, Vol. 30, #7, Oct. 1992, p. 438.
  • Alfred F. Leung, Simon George, and Robert Doebler, "Refractive Index of a Liquid Measured with a He-Ne Laser", TPT, Vol. 29, #4, Apr. 1991, p. 226.
  • T. A. McMath, "Refraction - A Surface Effect", TPT, Vol. 27, #3, Mar. 1989, p. 185.
  • Pu Bian, "Errata", TPT, Vol. 27, #2, Feb. 1989, p. 110.
  • P. J. Mejias, "Erratum: 'Measurement of Water’s Refractive Index' [Phys. Teach. 25, 166 (1987)]", TPT, Vol. 25, #9, Dec. 1987, p. 546.
  • Haym Kruglak, "Swimming Pool Optics", TPT, Vol. 25, #7, Oct. 1987, p. 440.
  • Paul Hewitt, "Figuring Physics", TPT, Vol. 25, #3, Mar. 1987, p. 180.
  • P. M. Mejas, "Measurement of Water's Refractive Index", TPT, Vol. 25, #3, Mar. 1987, p. 166.
  • Samuel Derman, "How the World Looks Underwater - A Demonstration for Nonswimmers", TPT, Vol. 20, #7, Oct. 1982, p. 474.
  • Philip DiLavore, "Reflection and Refraction at an Interface", TPT, Vol. 13, #4, Apr. 1975, p. 247.
  • Steven Janke, "Laser and Refraction Again", TPT, Vol. 11, #7, Oct. 1973, p. 388.
  • Ellis D. Noll, "Measuring the Index of Refraction of Liquids with a Laser: Experiment 1", TPT, Vol. 11, #5, May 1973, p. 307.
  • Nobuo Naba, "Demonstration of Refractive Index Measurement by a Laser", TPT, Vol. 11, #4, Apr. 1973, p. 241.
  • Kenneth S. Mendelson, "Apparent Shape of a Swimming Pool", AJP, Vol. 78, #12, Dec. 2010, p. 1254.
  • Edward Richard Van Keuren, "Refractive Index Measurement Using Total Internal Reflection", AJP, Vol. 73, #7, July 2005, p. 611.
  • Thomas B. Greenslade, Jr., "Reflection and Refraction Apparatus (Photo)", AJP, Vol. 71, #7, July 2003, p. 669.
  • Eric Stanley, "Generation of Conical Beams of Light for Smoke-Chamber Demonstrations", AJP, Vol. 49, #12, Dec. 1981, p. 1185.
  • "O-305: Water Tank & Scattering Medium", DICK and RAE Physics Demo Notebook.
  • "O-035: Chalk Dust, Smoke Box & Cream", DICK and RAE Physics Demo Notebook.
  • Freier and Anderson, "Od-1", A Demonstration Handbook for Physics.
  • Jodi and Roy McCullough, "Index Refraction with an Ocean Desk Toy", The Role of Toys in Teaching Physics, p. 3.23.
  • David Kutliroff, "7,8,9,10. Four Demonstrations of Refraction in a Fish Tank", 101 Classroom Demonstrations and Experiments For Teaching Physics, p. 32.
  • Borislaw Bilash II and David Maiullo, "Bend It, Bounce It", A Demo a Day: A Year of Physics Demonstrations, p. 339.
  • Michael E. Knotts, Edited by Karl Mamola, "Making Laser Beams Visible", Apparatus for Teaching Physics, p. 197.
  • Tik L. Liem, "Spear-Fishing, Anyone?", Invitations to Science Inquiry - Supplement to 1st and 2nd Ed. p. 89.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.