6A40.30: Disappearing crystals

Description: This demonstration shows what happens to an object (with index of refraction equal to water) when it is placed in water.

Equipment: Demonstration Procedure:
  1. Show the students the crystals (actually more like a jelly). Note that you can see them.
  2. Fill the small petri dish up with water.
  3. Place a few crystals into the water. Note that they "disappear".
  4. This happens because the crystals have the same index of refraction as water and because they are transparent.
  5. Since the light does not bend, it's as if there is nothing there, which makes it seem like there is only water.
  6. When finished, take out the crystals and let them dry off.
  7. A camera can be used with large classes, although it is not as dramatic.
Note: This can also be done with a swizzle stick that has the same index of refraction of water.