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Total Internal Reflection



Video Deomonstration Instructions

Fish Tank Demonstration

  • Obtain a fish tank (or another glass container such as a beaker or baking dish), milk or creamer, and a laser.
  • Fill a rectangular fish tank (or other glass container) 1/3 full of water.
  • Add a few drops of milk or creamer into the water, until the water is slightly fogged.
  • Point the laser toward the fish tank, moving it up until you find the critical angle.*

Water Bottle Demonstration

  • Obtain a clear plastic bottle (such as a water bottle or soda bottle), a tool to puncture a hole with, water, milk, tape, container, and a laser.
  • Puncture a hole approximately two inches above the bottom of the bottle.**
  • In a separate container, mix water with a few drops of milk, until the water is slightly fogged.
  • Cover the hole in the bottle and pour in the water mixture.
  • Place a container below the hole to catch the water mixture.
  • Point the laser through the bottle toward the hole.*
  • Uncover the hole, keeping the laser pointed toward the hole.

Fiber Optics Demonstration

  • Obtain a laser and fiber optic.
  • Point the laser at one end of the fiber optic.
  • Always handle fiber optics with care as they are made from glass.

Downloadable Lab

Students will discover the critical angle of an optic by measuring and testing several different angles. All lab experiments give students the opportunity to investigate, construct scientific explanations, and analyze their explanations. Labs are ready to download, print, and use!


*Lasers should always be used with caution and you should never look directly at a laser or point a laser towards anyone.

** Be careful while puncturing the hole in the bottle. Hold the bottle and the object you are using to puncture the hole away from your body and your hands.