Teacher’s Notes:
Activity Length – 50 min
Hook: Part 1 (5 min) Using a prism, demonstrate to students how white light is made up of all the
colors of the rainbow including primary colors red, green, blue (RGB). Position the prism near the
output reflector of the overhead projector. Remind students that many have seem something similar
before (rainbow) and that is how rainbows work. As white light goes from one medium (air) into
another (prism, or water droplets of a rainbow), the different colored light that makes up white light are
refracted (bent out at different angles, blue more so than red) as they exit out the other side of the
prism because of their different wavelengths. This gives the appearance that the colors are separated
out.
This can be further demonstrated with multiple color lasers (red, green, blue or UV). Using the same
prism, shine the lasers into the prism and watch where there beams exit. Do this for all three colored
lasers to prove the different angles of refraction.
Hook: Part 2 (10 min) Bring up the question to students, if we can separate white light into multiple
colors, can we combine multiple colors into white light? Most students will say yes and raise their
hands. Ask them where have they seen this. NOW, using the American DJ Par Can LED light, run
through the various primary colors going from all red, to all green, and then finally to all blue. Now
mix the colors red with green, then red with blue, and then finally green with blue. This will lead up to
the final hypothesis and the answer to the question you brought up earlier in class. Turn on all red,
green, and blue LED lights to see the result. WHITE LIGHT!!
Discussion: This is additive color mixing – meaning that we start with black and when all colors are
added together, the result is white. This is projected with light and is often used in lighting systems,
televisions, and projectors. On the contrary, there is subtractive color mixing, meaning that we start
with white and when all colors are added together, the result is black (or muddy brown). This is
typically used with paint and printers.
Step 5: Turn on the small speaker amplifier unit. Connect solar cell output into input jack of the
amplifier. Using any tv remote control, point at the solar cell and have students observe what happens.
(They should hear a continuous clicking sound). Using various barriers such as clear plastic, black
plastic, wood, paper, and glass, place it between remote control and the solar panel.
Thing to notice: Notice that with a black plastic (garbage bag) the IR signals are able to penetrate
through. Do a few samples for students and then let them do try out the rest on their own.
Suggest to students to try varying the distance between the remote controls and solar panels. This is to
demonstrate the inverse square law (1/r^2). Although it might be hard to notice, positioning the
remote controls twice as far should result in a signal that is ¼ of the original distance.
Name:_________________________________ Period:___________ Date:____________________
Visible Wave Energy – Light (Infrared, Visible)
Purpose: The goal of this lab is experience light of varying wavelengths and
how it affects the colors that we see and the colors we do not see (infrared)
Materials:
Prism
Overhead Projector
American DJ Mega Par RGB LED Light
Remote controls
Infrared Thermal Gun
Solar cell (Solarbotics model SCC2433B-MSE
$6.99)
Black garbage bag (UV light goes through it and
reflects back, unlike visible light)
Radio Shack Mini Amplifier with Speaker
(model 277-1008 $14.99)
Clear plastic bag
Paper towel
Shirt
Layer of sand
Red filter
Steps:
1) What are the 3 primary additive colors? ______________ ______________ ______________
2) What are the 3 primary subtractive colors? _____________ _____________ _____________
3) All electromagnetic waves, including light waves, travel at 300,000,000 m/s. Using the wave
speed equation and the chart above to estimate the wavelengths, calculate the frequency for red,
green, and blue light. (Show your calculations and your answer, otherwise, zero credit).
Color
Red
Green
Blue
Show Calculations:
Wave speed (m/s)
Wavelength (m)
Frequency (Hz)
4) Towards the left of the visible red wavelength, we move into a category of waves that are
referred to as infrared (below red). This is further divided up into two main categories, near
infrared and far infrared. Write down the approximate wavelengths for each. (Convert to
meters)
Near infrared (closer to red) ____________m
Far infrared (further from red)____________m
5) What is the difference between the two? Let’s demonstrate. The purpose of this next part is to
test hypotheses about what materials are transparent to visible light and infrared radiation (IR).
The reflective and refractive properties of IR also will be investigated.
Hypotheses: Place an X in the box if you think the material is transparent to visible light and/or IR.
Material
Clear Plastic Bag
Black Plastic Bag
Paper Towel
Shirt
Red Filter
Layer of Sand
Pass Visible Light?
Pass IR ?
Other Observations
6) Connect the solar cell to the alligator clips and plug the other end of the alligator clip wire into
the "Input" hole on the Mini Amplifier. Make sure the solar cell is facing up flat on the table.
Turn the volume up on the amplifier.
What do you hear? Place your hand over the solar cell, what happens?
7) The amplifier is making a humming sound because the ceiling fluorescent lights are actually
turning on and off 60 times a second. This is too fast for your eyes to notice but can be heard as
the voltage provided by the solar cell to the amplifier rises and falls 60 times a second. When
this light is blocked the sound stops.
Based on your observation, does the visible light from the ceiling lights able to pass through
your hand?
8) Take your remote control and point it at the solar cell. Press any button and then adjust the
volume on the amplifier so you don't annoy your classmates. Now point the remote toward
your eyes. (Don’t worry, it won’t blind you, I think.)
Based on your observations, does the solar cell detect something coming from the remote? Do
your eyes detect anything coming from the remote?
9) The remote control is producing IR that is invisible to your eye. However, when it hits the solar
cell it produces a current that flows into the amplifier and produces a sound. The solar cell
allows us to detect something that is invisible to us. Now place the objects listed in the
Hypotheses Table over the solar cell and determine if the ceiling light is passing through and/or
the IR from the remote can pass through. You may have to adjust the volume to hear the ceiling
light hum. Make any corrections to your hypotheses by circling misplaced Xs and adding any
left out. Try varying the distance between the remote control and solar panel to test out the
inverse square law (1/r^2).
Summarize below what you learned about how visible light and IR pass through the different
objects you tested.
10) Astronomers have difficulty learning about the center of our galaxy because the light from the
stars and objects is blocked by interstellar dust. How might they overcome this difficulty?
11) If astronomers want to study IR being produced by galaxies and other objects in the universe
they will need to build IR telescopes. Telescopes use mirrors and lenses to collect and
concentrate light. An IR telescope will only work if IR reflects from mirrors and refracts
(bends) when it passes through the glass in a lens. Use your mirror to try and reflect the signal
from the remote to the solar cell.
According to your observations, can IR be reflected by a mirror? Can you reflect it around a
corner to the solar cell? Try it.
12) Connect the solar cell to the alligator clips and plug the other end of the alligator clip wire into
the "Input" hole on the Mini Amplifier. Make sure the solar cell is facing up flat on the table.
Turn the volume up on the amplifier.
13) Hold the remote about 12 inches above the solar cell. Press a button and hold it. Place a
magnifying lens about halfway between the solar cell and the remote.
What happened to the loudness of the sound coming from the amplifier when the magnifying
lens is placed in the path? Is there a place other than the halfway point where it gets the
loudest? Try it.
14) Based on your observations, do you think astronomers can build IR telescopes?
Conclusion: Summarize what you have learned about the properties of IR below. Give at least 2
reasons why astronomers are interested in studying IR coming from galaxies and other objects
in the universe.
http://science.hq.nasa.gov/kids/imagers/ems/infrared.html