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Refraction

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Fish Hunting

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 caught a meal. To be successful hunters, birds must use the principle of refraction to determine where the fish are located before a strike is made. By recognizing that fish are located in a different spot than what their eyes perceive, herons can accurately determine where to strike.

News You Can Use

  • Light travels in roughly a straight line as it passes through the air. When it hits an interface that separates two different types of media, such as air and water, part of the light is initially reflected and the rest enters the medium. If the the light source is not normal to the interface, the part 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, light traveling into a medium with a higher index of refraction 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 deviate from the initial path light before it entered the glass?

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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