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