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Refraction: To Bend or Not to Bend?

  • Introduction
  • Video& Results
  • Materials
  • Procedure
  • Preparation & Notes
  • Download Files

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Often when light passes through different substances, it changes speed.  This change in speed appears to us as a change in the direction of the light, or bending.  For example, when a straw is placed in a glass of water or juice, it appears to beglass strawnd below the surface of the drink.  The bending of the straw is because air and the drink have different values of Refractive Index.  

 

 

Results, Images & Video Demonstrations
Activity 2: Disappearing pyrex stir rod

pyrex_glass

(Left) Pyrex stir rod in canola oil (Right) Pyrex stir rod in water.
The pyrex stir rod is invisible in oil because pyrex and canola oil have nearly identical indices of refraction.


 

Activity 3: Curving green laser light in a corn syrup gradient

sucrose_gradient

80% sucrose and water have different indices of refraction. A tank is layered with corn syrup and then water and allowed to sit undisturbed for 24 hours. The corn syrup diffused into the water later creating a gradient of sugar concentration with a corresponding gradient of index of refraction. A laser beam pointed through the solution is bent a different angles and curves.The beam shown is reflected off the bottom of the tank and curves back up.


This video expands on these concepts and gives a very clear demonstration of Snell's Law.

 

Materials – Refractive Index

Bending light in water

  • tank of water
  • 1 packet non-dairy creamer
  • laser pointer

Disappearing Stir Rod

  • pyrex stir rod
  • glass stir rod
  • canola oil
  • water
  • 2 glasses

Curving light in a sucrose gradient

  • 2.5 lb bag of sugar
  • 4 liters warm water
  • tank of water
  • laser pointer

Activity 1: Bending Light in Water

  1. Pour water into a clear glass tray, like a brownie pan or lasagne pan.
  2. Sprinkle non-dairy creamer or pour a small amount of milk into the water.
    The milk has particles that reflect the laser light, making the beam visible.
  3. Shine the laser beam into the water vertically. Is the beam straight?
  4. Shine the laser beam at the water at an angle and study the angle of the beam as
    it enters the water. What happens to the beam as it crosses from air to water?

Activity 2: Disappearing Stir Rod

  1. Pour canola oil into one clear glass and water in a another glass.
  2. Place glass and pyrex stir rods in the glasses.
    What do you see? How is the oil different than water? How do the glass and pyrex stir rods compare?

Activity 3: Curving Light in a Sucrose Gradient

  1. Pour corn syrup into the bottom of a long clear tank to a height of 2-3".
  2. Pour warm water over the corn syrup and allow the tank to sit for 12-24 hours. Warming the water will help dissolve the corn syrup (on bottom) into the water layer (top).
  3. Shine laser light into the tank where the corn syrup and water meet, the beam will curve as you move it up and down. We mixed in some milk so that the red laser beam could be seen.

References
A cool experiment with bending light in sugar water is described at Buffalo State University and in more experimental detail at Harvard University.

A list of indices of refraction is available online. A few are listed below.

Index of Refraction
Medium n
air 1.00
water 1.33
80% sugar water 1.5
canola oil 1.47
pyrex 1.474
glass (fused silica) 1.459