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Refraction

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Fish Hunting
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Fish Hunting

Credit: Terry Foote
Source: http://en.wikipedia.org/wiki/File:GBHfish5.jpg
License: CC BY-NC 3.0

After searching the waters, this great blue heron finally catches a meal. To be a successful hunter, the heron must use the principle of refraction to determine where the fish are located before a strike is made. By recognizing that the fish are located in a spot that is different than what its eyes are telling it, the heron is able to accurately determine where to strike.

News You Can Use

  • As light passes through air, it travels in nearly straight line. When light hits an interface or a boundary that separates two different types of media, one part of the light is reflected and part of the light enters the medium. If the incident light is not normal to the interface, the light that enters the different medium will not be parallel to the incident light. The change in the direction is known as refraction. To determine how light will behave in a given medium, you need to look at the medium's index of refraction.
  • The index of refraction describes how radiation would propagate through a given medium. To determine the index of refraction you would calculate the ratio of the speed of light to the speed of light in the medium. As an example, air has an index of refraction of 1, while water has an index of refraction of 1.33. Since water has a higher index of refraction this implies that the velocity of light moves a little bit slower in water than it does in air.
  • As a general rule of thumb when light travels into a medium with a higher index of refraction, the light will be bent towards the normal of the surface. 

Show What You’ve Learned

Using the information provided above, answer the following questions.

  1. If the heron in the picture above saw a fish sitting still in one spot, where should the heron aim for the fish?
  2. Would light bend towards or away from the normal of the surface if it traveled into a medium with a lower index of refraction?
  3. If light were to enter a small layer of glass (n=1.50) and then exit the other side, how would you expect the path of light to be deviated from the light before it entered the glass initially?

Image Attributions

  1. [1]^ Credit: Terry Foote; Source: http://en.wikipedia.org/wiki/File:GBHfish5.jpg; License: CC BY-NC 3.0

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