6A40.70-Beer Mug Refraction

6a4070beer mug refraction

Description: This demonstrates refraction at an air/water surface. Reveals the tricks of bartenders.


  • Medium sized plastic container
  • Three different beer mugs
  • Three different food colorings
  • Water

Setup Procedure:

  1. Place a drop or two of food coloring in each beer mug. Use a different color for each.
  2. Fill the beer mug up with water.
  3. Place them in the plastic container and spread them out.
  4. Fill the plastic container to about 2/3 the height of the beer mugs (See picture).

Demonstration Procedure:

  1. Have students look at the setup.
  2. Explain that form the water-glass-air path, it looks like the liquid is almost to the side of the beer mug.
  3. When looking at the water-glass-water path, you can see the inside glass wall of each beer mug.
  4. This is a common trick used to make the buyer think they are getting more beer than they really are.