The Bending of Light


This demonstration is to reinforce the lesson on lasers and how laser light is different from white light because of the behavior of the wavelengths. 


A laser beam has waves that all have the same wavelength, or color.  The waves move together with the crests and troughs aligned with each other.


White light, on the other hand, has wavelengths of all different sizes, or colors, and they are scattered (travel in all directions).



         2-liter bottle



         Milk (skim works best)

         Laser light




1.     Make a hole about 8 cm from the bottom of the 2-liter bottle. (It works best to heat up a nail and push it through the plastic.  This makes it a smooth opening).

2.    Cover the hole with tape.

3.    Fill the bottle about two thirds full of water.

4.    Put about 3 – 4 Tablespoons of milk into the bottle.

5.    Make the room as dark as possible (the darker the room, the easier to see the laser light).

6.    Remove the tape from the hole.

7.    From the opposite side of the hole, point the laser pointer directly through the bottle and at the hole.  The light should follow the stream of water and bend.

8.    Discuss with the students why the light is behaving this way.  This happens because the light is being totally reflected within the water.