Introduction to Light

Question:

What are the properties of light?

Materials:

Station 1

  • White flashlight
  • Red, green, and blue flashlights
  • Diffraction gratings
  • Transparencies

Station 2

  • Solar cell kit
  • Multimeter
  • White flashlight
  • Red, green, and blue flashlights
  • UV flashlight
  • Polarizers
  • Transparencies

Station 3

  • Polarizers
  • Computer
  • Corn syrup

Station 4

  • Spinach and other vegetables
  • Beakers
  • IPA
  • Blender
  • Sieve
  • UV light (395 works best)
  • White flashlight

Station 5

  • Invisible ink pens
  • Sunblock
  • UV light (nice to have a few different wavelengths- we used 365, 395, 254 nm)

Instructions:

Station 1

  1. Ask the students what color they’ll see if they combine the blue and red transparency. Go through the different binary combinations.  Ask what color they’ll see if they hold all three transparencies over a light source.  This should tap into their previous knowledge of mixing paints.
  2. Now ask the students to hypothesize what color the light will be when the red and blue lights are mixed together. Go through the different binary combinations.  Ask what color the light will be if they add all of the lights together.
  3. Use the diffraction gratings to look at different light sources around the room.

Station 2

  1. Introduce the students to the solar cell set up. Start with the radio and have them explore under what conditions the radio plays, at what the volume etc.
  2. Move onto the solar cell kit hooked up to the multimeter, explain the output of the meter. Have them test the output of the solar cell with different colors, light sources, distances- really whatever they want to do.

Station 3

  1. Have the students bring the polarizers over to the window and hold them up to the light. Instruct them to rotate the single polarizer.  Ask them what they observe.
  2. Have the students rotate a second polarizer over the first. They’ll find an orientation that blocks out all of the light.  Have them describe what’s happening.
  3. Show them the applet comparing light to a rope going through a fence.
  4. With the first two polarizers oriented as to block out all light, have them investigate the effect of a third polarizer.
  5. Show them the second applet with the three polarizers demo.
  6. Have them shine polarized light through the corn syrup. On the other side of the jar, have them rotate a second polarizer, they should see different colors at different angles.  Have them try different set ups.  No polarizer at the beginning, rotating the first polarizer instead of the second etc.
  7. Have them go around the room looking for polarized light sources (the computer or their phone screens are good examples.)

Station 4

  1. Take a small handful of spinach leaves and place in the Nalgene beaker. Add ~70 mL IPA.  Carefully, blend the spinach leaves.  Pour into another vessel through the sieve.  Under the tarp, shine the mixture with UV light.  Shine the mixture with regular light.
  2. Blend up cauliflower heads. Does it respond in the same way to the UV light?

Station 5

  1. Give each student a piece of paper and have them write a secret (and appropriate) message with the invisible ink pens- tell them to write lightly otherwise the ink won’t dry and you’ll be able to see the message in regular light. Let the ink dry for a minute.  Shine the different UV lights and the regular light on the secret messages.
  2. Have them spread a thin layer of sunblock over part of their message. Shine the different UV lights over the sunblocked area.  Ask them to conclude which light is the most dangerous to humans.
  3. Test the different UV lights on the glasses at the station. If one of them has glasses test whether or not the lenses are UV protective.