Applied Science - Physics (5B)
Pre Lab 

   
OBJECTIVES:
  • Discovering the components of light.
  • Observing and explaining optical illusions.

VOCABULARY:

  • illusion
  • prism
  • reflection
  • refraction
MATERIALS:

Students determine how light creates illusions.

BACKGROUND:

Emphasize that this segment concentrates on visible light which is a part of the electromagnetic wave spectrum. Review how light carries energy in tiny packets of electromagnetic radiation called photons. Light travels at 296,000 meters per second or 186,000 miles per second and doesn't need a medium to travel in. All colors of light travel at the same speed, but they have different wave frequencies (short and long waves).

Light can be reflected or refracted. In reflection, light bounces off a surface and is diffused. Light travels in a straight line and refraction is the bending of this light. The light breaks up into different frequencies therefore causing a rainbow or a "broken" look.

This activity demonstrates different components of refracted light. If students do not know the light spectrum, give them the following pneumonic device to help them remember. ROY G. BIV = red, orange, yellow, green, blue, indigo and violet.

PROCEDURE:

  1. There are several optical illusion Internet sites. You may want students to look at the following site http://www.illusionworks.com/  or you may want to print some out and go over the different illusions and discuss why they see them differently. The reason is because the way our eyes detect black and white light.
  2. Read Light Magic to students if they need a quick review of properties of light. 
      
  3. Demonstrate for students the following:
      
    DEMONSTRATION 1. REFRACTION IN WATER. 
    Place a piece of waxed paper over a printed page. Using an eye dropper, put a few drops of water on the waxed paper and observe. Ask students to describe what happens. The drops of water act as a lens and refract the light which distorts the image.
      
    DEMONSTRATION 2. ILLUSIONS (REFRACTION). 
    Place a penny underneath (not in) an empty plastic cup. The penny should be visible through the side of the cup. Looking into the cup, keep your eye on the penny as your partner slowly pours water into the cup. (Be sure not to move your head). Ask students what happens. The penny appears to be in a different position. Immerse a pencil in the plastic cup of water. Look at it from the side, it appears to be broken. Another illusion!
      
    DEMONSTRATION 3. REFRACTION IN A PRISM. 
    Light is bent twice when it passes through a prism and the separation of color is quite noticeable - a rainbow. The prism separates the frequencies of light, so a rainbow appears. What colors can you separate from the white light? If your classroom has bright sunlight that is a good source of light; otherwise use a flashlight. Light must be shone correctly through a prism in order to get a rainbow.

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