6A44.20-Critical Angle

6a4420critical angle

Description: This demonstration shows how light transmits through materials differently based on incident angle


  • Large glass container
  • High intensity Laser
  • Portable stand
  • S clamp
  • Water
  • Milk powder

Setup Procedure:

  1. Fill the tank up with water.
  2. Add a little bit of powdered milk. Mix it in.
  3. Mount the laser on the stand. The high intensity laser must be used for this to be most effective.
  4. Aim the laser into the tank so that total internal reflection occurs. Plug in the laser.

Demonstration Procedure:

  1. Turn on the laser.
  2. Turn off the lights.
  3. Note that the laser beam experiences total internal reflection, and travels down the container walls.
  4. When finished, turn off the laser.

Laser Light Laser Light
Do not stare at the laser beam. Do not point the laser at students.

Note: This picture is time elapsed. In person, the beam will not be as bright.