Introduction

Procedure

• Gather these items from your home or workplace:
  • a water glass
  • a flashlight, or other directed beam of light
  • a round-bottomed flask, or some spherical glass container (a round fishbowl would work)
  • a small piece of cardboard or posterboard that fits over the head of the flashlight
  • a 10"x14" piece of white posterboard

• Place the glass filled with water near the edge of a table that is bathed in sunlight. As in the drawing below, a "rainbow", or spectrum, should appear on the floor near the glass. If the sun is low on the horizon, look for the spectrum on the wall!
  

• What is the glass and water doing to the light? Visit the Rainbow Readings to find out...Return here when you are finished.

• Let's repeat our experiment with the water and the light. This time we need to use the round container, the flashlight, and the small and large pieces of cardboard.

• Cut a narrow slit in the small piece of card/poster board and tape the piece to the head of the flashlight, so that only a small beam of light emerges

• Now cut a fist-sized hole in the middle of the large piece of posterboard. Also fill the spherical container with water.

• Shine the narrow beam of light from the flashlight through the hole in the posterboard and onto the container. You may need an extra person to hold the container while you shine the light and hold the white posterboard.
  

• What do you see on the container-side of the posterboard as you shine the narrow beam of light onto the water-filled flask? Can you position the flashlight and container so that you see a spectrum on the white paper?

• What is the shape of the spectrum on the piece of posterboard? How is this similar to a rainbow in the outdoors? How is it different?

• If you have access to a garden hose, a sprinkler, and a water spout, go outside and try to make your own rainbow!
  
  • Get a fine misting sprinkler and set the water pressure high enough to get a large volume of water droplets in the air.
  • Based on what we've learned up to now, where should you stand with respect to the water and the sun?
  • Find the shadow of yourself on the ground. Try to measure the angle from the shadow of your head to the rainbow arc. Use the "hand and fist" method to measure this angle: if you stretch out your arm and make a fist, the width of your fist is about ten degrees; the width of a finger at arm's length is about two degrees. Try it!