Refraction Action

Materials: Computer and School Network

Time Allotment: 3 Class Days

Purpose:

The purpose of this activity is to explore a variety of refraction effects and to make an attempt to explain them using some simple refraction principles and some ray diagramming.

Part 1: The Sleepy Driver

Consider the following thought experiment (which corresponds to an experience which you may have had).

Ben Laborin has just completed the graveyard shift (11 pm to 7 am) at the local factory. On his drive home he becomes tired and momentarily falls asleep. His car gradually veers to the side of the road. Finally, his right front tire passes from the blacktop road onto the gravel XXX. His car suddenly begins to turn further to the right. The sudden noise of a tire on gravel and the sudden change in direction of the car awakes Ben and he naturally responds by jerking the steering wheel to the left and returning to the blacktop road.

  1. As Ben's front tire passes from the blactop to the gravel, do you suppose that it will speed up or slow down? ___________ Explain.

     

  2. If a car tire travels from a fast to a slow surface, then it will change its direction ____________ (towards or away from) the interface of the two surfaces.

     

  3. If a car tire travels from a fast to a slow surface, then it will change its direction ____________ (towards or away from) the normal drawn to the interface of the two surfaces.

     

  4. Complete your understanding by drawing an arrow to show the direction which Ben's car would travel if he drove completely off the road and never woke up.

Part 2: The Refracted Light Ray

In the above analogy, Ben Laborin's car changed speed and direction as it passed from one surface (blacktop) to another surface (gravel). The above analogy can be extended to understanding the behavior of light as it passes from one material to another. Ray Zuvlite takes a laser pen and shines the beam at a 45-degree angle from air towards the water-filled fish tank.

  1. Based on textbook reading and class discussion, do you believe that the light will speed up or slow down as it passes into the water? ___________________ Explain the rationale for your answer.

     

     

  2. Based on textbook reading and class discussion, do you believe that the light will bend towards or away from the normal as it passes into the water? ___________________ Explain the rationale for your answer.

     

     

  3. Express your understanding of the direction of light refraction by drawing the refracted ray for the following situations.

 

Part 3: The Broken Pencil

Obtain a clear drinking glass and a pencil or pen. Fill the glass three-fourths full of water. Place the pencil in the water in an upright position. Place the water at eye level (or better yet, your eyes at water level). Slowly move the pencil from side to side, observing the appearance of the pencil both above and below the water.

  1. Describe your observations and complete the diagrams for when the pencil is held in the exact center of the beaker, slightly off-center, and near the edge of the beaker.

     

     

  2. Propose an explanation for your observations. (Perhaps it would be helpful to read the chapter for our current unit. What an idea!)

     

     

     

     

  3. Cy Klops is doing the Refraction Action makeup lab. A top view of the glass of water, pencil, and Cy's eye is shown. In order for Cy to see the image of the pencil in the water, a ray of light must travel from the pencil to his eye. For each pencil position, a ray of light from the outer perimeters (left and right) which utilimately rach Cy Klop's seyes are drawn. (Note, that Ray is unable to see the left side of the pencil in the third diagram.) Complete the diagram by drawing the refracted ray to Cy's eye and extending the refracted ray backwards to approximate the location and width of the image of the pencil.

     

  4. Explain how the features of the above ray diagram explain the observations which you made in #1.

 

 

 

 

Conclusion:

Write a paragraph in which you define refraction in simple terms, explain when refraction takes place, explain why refraction takes place, state a general rule for predicting the direction which a light ray will refract, and explain the value of such a rule in explaining a refraction phenomenon (other than the one discussed in this lab). Do a bang-up job!


 

 

 

 

 

 

 

 

 

 

 

 


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This page created by Tom Henderson and last updated on 8/25/97.