Advance Preparation and Setup

Make one copy of the Blackline Master for each student. There are many kinds of gelatin you can use. Let the gelatin harden in a rectangular tray and cut out the blocks in advance. Take care to cut the blocks as precisely as possible. You can run hot water on the bottom of the tray to soften the bottom of the gelatin so the blocks will come out easily. Keep them wrapped and refrigerated until the lab so no microorganisms will grow on their surface. Be sure you have supports for the gelatin and the light source so they are at the proper height to permit light beams to go through the gelatin block. If your students are using lasers, find large pieces of cardboard for laser backstops. If you have neither a laser nor a ray box, each group can use a candle and a narrow (2 mm to 3 mm) slit in a piece of cardboard. With this arrangement the students can at least get semiquantitative data and observe total internal reflection.