The Refracting Case of the Disappearing Test Tube

Don’t believe in cloaking devices? Then make one yourself!

Materials needed:

  • 1 large transparent container – a cup works well!
  • 1 Pyrex* test tube or small Pyrex beaker that can fit inside the larger transparent container
  • vegetable oil

*Note: Pyrex MUST be used in order for this experiment to work!

Procedure:

  1. Fill the large transparent container ¾ full with oil.
  2. Fill the pyrex test tube/beaker with oil
  3. Place the pyrex test tube/beaker inside the larger transparent container. The test tube/beaker should disappear!

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How does it work?

Light can bend when it passes through certain solids/liquids (eg. water, oil). We see objects when light hitting these objects reflect into our eyes. When we see glass, we don’t see the glass object itself but through other objects in the room are reflected/distorted by the glass. The test tube/beaker disappeared because both Pyrex and vegetable oil bend (refract) light by the same amount – light travels straight through both materials! Therefore, there was no way for light hitting the test tube to bend or reflect back into your eyes.