A Self-Guided Tour of the Electromagnetic Spectrum
Introduction: The goal of this exercise is to learn about the electromagnetic spectrum. Included with this are the
technical details as well as practical examples.
Open Internet Explorer to the following website: http://www.pbs.org/wgbh/nova/gamma/spectrum.html
Click on the link that says: A Self-Guided Tour of the Electromagnetic Spectrum
If the window at right does not come up right away, you may have to install
Flash. Please follow the prompts to do so.
When you get the introductory screen, you may “begin the tour”.
The page at left shows the
next screen. The pop up in the
middle of the page appears
when you hover over the leftmost picture. This gives
specific information to the
picture your mouse is
hovering over. You will
answer a series of questions
based upon changing pages
and hovering over pictures to
get specific screens as well as
information and graphics on
the main screen.
Please note that sometimes
the acronym EM is used to
stand for the long word
“Electromagnetic”.
1. Look at the EM spectrum scale. What are the names for EM radiation with the greatest frequency waves and
the smallest frequency ones?
Gamma, radio
2. Don’t look at the next page yet and answer this yes or no: Do you think you can hear radio waves? no
Radio Waves
3. Many people think they hear radio waves. Actually, nobody can. Radio waves are part of the
electromagnetic spectrum and really are another variety of light. Your radio can take radio waves and create
sounds based on the information within the signal. You hear vibrating air emitted from the radio’s speakers,
not the radio waves themselves. Sound travels at 340 m/s, how fast do radio waves travel?
The speed of light
4. Michael Jordan is 2 m tall. Read the information about the size of radio waves and decide if it’s possible to
have radio waves whose wavelength is as big as Michael Jordan is tall? (Explain how you know this)
Yes, they range from 1 m to 10,000 km
5. Is it possible to have radio waves smaller than an inch? Justify your answer to this.
No. must be > 1 m
6. How do we make man-made radio waves (what physical thing actually moves)?
Electrons moving (vibrating)
7. Name the five different radio bands (frequency ranges).
Commercial, government, aviation, maritime, two-way radios
8. What name do we give to the low frequency waves that broadcast television signals?
Radio waves
Microwaves
9. Microwaves are used with radar to track speeds of what two moving objects? (Police radars are not perfect.
If you are interesting in knowing more, check this site out: http://www.magma.ca/~fyst/appndxc.htm)
Planes and speeding cars (police)
10. What was invented in the 1930’s that allowed people to create microwave frequency radiation easily?
Magnetron
11. Radar is an acronym for something, what do the letters RADAR stand for? (It’s a palindrome too!)
RAdio Detection And Ranging
12. What molecule in most foods heats up when exposed to microwave radiation? (it absorbs microwave
energy)
Water
13. Name a daytime object and a night time object that emit microwave radiation?
Sun, stars (not moon, it reflects, doesn’t emit microwaves)
Infrared (also see http://www.teachersdomain.org/9-12/sci/phys/mfw/irgallery/popup.html)
14. Did you know you give off EM radiation? That’s right, heat gives off EM radiation. That’s how soldiers
find the bad guys at night. Hey, you can tell all your friends you’re hot! Which part of the EM spectrum
gives off heat?
Infrared
15. When a radiator, or anything, gets hot enough so it gives off visible light, what color light does it give off
(what part of visible light is CLOSEST to infrared)?
Red
16. Global warming isn’t really caused from more heat being produced on earth or reaching us, it’s caused
because greenhouse gases make it harder for the earth to lose its infrared radiation. This is how earth gives
up energy, or cools off. Stars also give up some infrared energy too. Beginning with the letters D and G,
what material within Orion’s constellation gives off infrared energy?
Dust and Gas
17. How does infrared help us to be better couch potatoes? (Hint: what device uses IR signals?)
Remote controls
18. Infrared radiation is invisible to us. Nature just didn’t build us that way. Its initials are V. C. What manmade device that you probably have at home can “see” the infrared radiation we can’t?
Video Camera
Visible Light
19. Ever hear of a Retina? I hope so. You have two of them on the back of your eyeball. What kind of EM
radiation is your retina really good at detecting?
Visible light
20. We’ve already mentioned that you’re hot. Hot enough to give off IR radiation. However, you’re not hot
enough to give off visible light, like a light bulb’s filament. Up to what temperature is the filament?
3000 C
21. Compared with IR and radio waves, how big are wavelengths of visible light? (it’s shorter than the width of
a _____)
Much smaller, shorter than the width of a bacterium
22. Which part of the EM spectrum do some laser lights use?
Visible light (as well as IR and UV)
Ultraviolet
23. UV radiation can be useful for sterilizing medical equipment because it kills what two things?
Bacteria and Viruses
24. When UV radiation strikes phosphor powder, what kind of radiation does the phosphor powder re-emit?
What’s the name we give to a light bulb that works like this?
Visible light. Fluorescent light.
Ultraviolet (continued)
25. This is not on the website, so deduce this one with that 3 lb thing between your ears and what you’re learned
so far: UV light is what causes sunburns, suntans and damages our skin. You can stop this by applying
something that absorbs UV light, instead of letting it reach your skin. What do we call this?
Sunscreen
26. Humans and planet earth emit infrared. A light bulb is hotter and emits visible light. The sun is hotter still.
The sun emits lots of visible light, but what kind of EM radiation do the hottest parts of the sun emit?
UV radiation
X-rays
27. Who discovered X-rays and in what year?
Wilhelm Roentgen, in 1895
28. How does the frequency of X-rays compare to visible light (higher, lower, same)?
Higher
How does the wavelength compare to visible light? (bigger, smaller, same)?
Smaller
29. Since X-rays are much smaller than visible light, they are small enough that a lot of their energy can pass
through some materials, since they’re smaller than the molecules of those materials. Beginning with M,
what science takes advantage of this to help see what ails sick people?
Medicine
30. Have you noticed by now that the hotter something is, the smaller the wavelength of radiation it emits. What
can you say about the temperature of the clouds of gas that surround supernova explosions?
Extremely hot
31. X-ray radiation kills both cancer cells and normal cells. Why is it used to treat cancer?
It kills cancer cells faster.
Gamma Rays
32. What are the two ways gamma rays are created on earth?
Decay of radioactive particles and in particle accelerators
33. Is it true that gamma rays are among the most common, if not the most common; or, is it just the opposite?
False, they are scarce
34. Do you think it takes something cool to emit gamma rays, or something extremely hot (like a violent
explosion)?
Extremely hot
35. If it’s rare in the universe for anything to get hot enough to create gamma rays, then you might imagine
would take a long time to take a picture in the sky of gamma radiation. How long did it take to make an
image of the entire sky while waiting around for enough of this rare radiation to reach gamma ray sensitive
film?
18 months