Invisible Glass Rod

The point of this demo is to discuss how refractive index affects light.  This point is demonstrated by inserting a solid object into a liquid that has the same refractive index as the solid.  As light passes through an object of a different refractive index, the light bends.  However, in this example, the light will not bend as it moves from the liquid to the solid, which makes the object appear invisible.  An overview of this demo with a short video can be found here.  Here is what you will need:

  • 1-2 pyrex glass bowls
  • Vegetable oil
  • A small pyrex object that will fit in at least one of the bowls

This demo can be done in one of two ways.  You can either take a pyrex bowl and make it dissapear, or if you only have 1 pyrex bowl you can find another object to make disappear (our group uses pyrex glass rods!).

What to do: Take the largest pyrex bowl and fill it up with enough vegetable oil to submerge your second object into (rather it be another bowl or rod or whatever).  Once the bowl is filled with enough vegetable oil, slowly place the second object inside and watch as it disappears right before your eyes.  Make sure to nail the point home by submerging a different glass object into the oil.  As long as it is not pyrex glass it will not disappear, and you can explain how the refractive index makes the light bend, thus making the object visible.