The Magic of Optics: Now you see it, now you don't part of comPADRE Pedagogic Library:Teaching with Interactive Demonstrations:Examples
This interactive lecture demonstration is used as an introduction to the concept of refraction. A piece of Pyrex tube seems to disappear when submerged into a beaker half-full of mineral oil because Pyrex and mineral oil have a highly similar refraction index. The same Pyrex tube is clearly visible in a beaker of water. Usually, this demonstration is used as an example of refraction (or lack thereof) after the topic has been introduced. However, a different, magical approach is suggested here to better engage students. Students are presented with a "magic" liquid that binds broken pieces of glass back together. The instructor takes a Pyrex tube and after carefully wrapping it well in brown paper, proceeds to smash the test tube with a hammer. The remaining fragments are poured into a beaker filled with the "magic" liquid (which unbeknownst to students has a hidden intact Pyrex tube submerged). After a little stirring, the instructor pulls out the fully "repaired" Pyrex tube with a pair of tongs. Students are guided through an inquiry cycle (is this liquid to good to be true?) through which the concept of refraction is constructed and the magic trick debunked.