Invisible Light
Goal: Discover the colors of visible light and learn how to detect invisible forms of light just beyond the visible spectrum.
Appropriate for all ages. You'll need a bright sunny day to run this experiment.
Materials: A prism or diffraction grating, a thermometer, UV-reactive beads, tape, a tissue box (or similar) and a pair of scissors.
NGSS Recommendations:
Kindergarten - Weather and Climate, Natural Hazards, K-ESS3.B
1st grade - Light and Sound, 1-PS4-3
2nd grade - Structure and Properties of Matter, 2-PS1.A
K-2 Engineering Design - Detecting light
Background:
When you mix all the colors of paint together in art class, you get a brown/black mix. But light works differently. If you mix all the colors of light together, you get white light. White light from the Sun or lamps in your house is actually a mix of all the colors of the rainbow. You can break light back up into a rainbow by looking at the light through a prism or diffraction grating, like the glasses in the kit.
Don't use the peephole to stare at the Sun! They won't protect your eyes. Look at reflected light instead, or a lamp in your house.
Procedure #1 (inside):
Look through the diffraction peephole at a light source (not directly at the Sun!).
Observation #1:
You should see the light broken up into rainbows!
Procedure #2 (outside on a sunny day):
Poke a hole in the middle of the heavy paper (cardstock, cardboard, foam board, etc.) using a pencil or something that will make a similar-sized hole. Tape the peephole to the hole in the paper.
Place the white paper under the heavy paper to catch the circle of light and shade around it.
Use the magnifying glass to direct a bright beam of sunlight through the peephole.
You have a sensor that detects IR light (thermometer) and a sensor that detects UV light (the beads, which change from white to colorful in the presence of UV light). Try moving both the thermometer and the UV beads around the rainbow (and just outside of it) and see what you discover! Note that both the thermometer and beads can take 10+ seconds to adjust their readings when moved to a new position.
Observation #2:
The thermometer should read the highest temperature where the IR light is concentrated, just beyond the red of the rainbow. The UV beads should show the brightest colors where the UV light is concentrated, just beyond the blue part of the rainbow.
Science:
When light passes through a prism or diffraction grating, it bends (this is called "refraction"). Some colors of light bend more than others, producing a rainbow effect as the red light separates from the blue and we can see all the colors in between. The rainbow you see through the glasses are all the colors of "visible light", from red to violet.
But there's more there we can't see with our eyes! On one side of red light, we see orange. On the other side of the red light is infrared (IR) light, invisible to our eyes - but not to an owl! Owls and other nighttime predators can see IR light, which is produced by animals (including you!) in the form of heat.
On one side of the violet light, we see blue. On the other side of the blue light is ultraviolet (UV) light, invisible to our eyes - but not to bees! Bees use their UV sight to recognize patterns on flower petals, invisible to us, to help them figure out the best place to land on flowers. Further beyond the infrared, you'll encounter radio waves. Radio waves are a kind of light we use to transmit information and communicate, including to radios (devices that turn light into sound), internet, and cell phones.