Bending light
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Materials needed:
Plastic pitcher
Sink
Water
Nickel
Water glass
Pencil
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Do you think you can bend light? In this experiment you will try to use water to make light go around a corner.
Place an empty plastic pitcher in a sink under a water faucet so that you can add water to the pitcher without moving it. Put a nickel in the bottom of the pitcher. Move the nickel until it is touching the side of the pitcher toward the front of the sink. Begin with your head directly over the pitcher so you can see the nickel inside the pitcher. Now, slowly move your head back, away from the sink, until the nickel completely disappears. You must stay very still and keep your head in exactly the same place for the rest of this experiment.
While holding your head steady, turn on the faucet to allow water to flow. As the water fills the pitcher, continue to look at the bottom of the pitcher. When the water has nearly filled the pitcher, turn off the faucet to stop the water. Do not move your head. Where is the nickel? Can you see it?
You probably observed that as water was added to the pitcher, the nickel seemed to move. The nickel could not be seen at all when the pitcher was empty and the side of the pitcher blocked your view. However, when the pitcher was filled with water, you should have been able to see the nickel even though you had not moved your head. Can you explain this change?
In order for you to see the nickel in the bottom of the pitcher, light striking the nickel must reach your eye. Light normally travels in a straight path, and when the pitcher is empty the light reflected off the nickel travels straight to your eyes. When you move your head back, the side of the pitcher blocks the light and you cannot see the nickel. However, when water is added to the pitcher, the light no longer travels in a straight line, but is bent.
Light waves are bent when they travel from water into air or air into water. Refraction, the bending of light, occurs whenever light goes from one substance into another. The light is bent when it goes from air to water because light waves travel more slowly in water than in air. Two substances in which light travels at different speeds will cause refraction if the light goes from one substance to the other at an angle (not straight).

Scientists use the index of refraction as a measure of how much light bends when it passes from one substance into another. The index of refraction is the ratio of the speed of light in a vacuum to the speed of light in specific substance. A device called a refractometer can measure this extent of bending. Measuring the index of refraction with a refractometer is one-way scientists identify unknown liquids or determine the amount of liquids in a mixture.
When light passes from air into glass and then out of the glass, it can be bent. Different colors of light are not bent by the same amount, and so the effect of this bending, or refraction, is to spread white light into the colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet.