Download 1-1A Spectrum The most familiar kind of light is visible light—such

1-1A
Spectrum
The most familiar kind of light is visible light—such as red, yellow, and blue. Our eyes
are only sensitive to a small range of light. Stars, for example, produce a much wider
range of light. Radio, microwave, infrared, ultraviolet, x-ray, and gamma ray light are all
ranges of light that are invisible to the eye. However, studying this radiation is very
valuable. For example: x-rays penetrate the soft tissues of the human body and are used
for taking pictures of bones, radio waves transmit (you guessed it) radio signals, and
microwaves warm food and pop popcorn. Invisible light waves are constantly zipping by
you. In this section of background information, the electromagnetic spectrum will be
explored in general.
Wave basics
One model of light is that light is a wave. To visualize a wave, imagine a stretched-out
rope. A person holds one end of the rope and wiggles his hand back and forth. The
resulting wave might look something like the picture below.
Notice that the high points—or crests—are spread apart. The distance between crests is
called the wavelength. If the person shook his hand back and forth faster, the crests
would be closer together. In other words, the wavelength would be smaller. This is a
very important concept. For waves that go at a certain speed, having waves go by more
frequently means that they are shorter in wavelength. Shorter wavelengths have a higher
frequency. Notice on the picture below that the wave on the right has a shorter
wavelength—and hence higher frequency—than the wave on the left.
Light as a wave
In many ways, light is like a wave on a string. Light can have very high frequencies,
very low frequencies, or something in the middle. Very high frequency light is very
energetic. For example, ultraviolet light is higher frequency than visible light. It has
more energy than visible light. As a result, ultraviolet light can give sunburns! Lower
1-1A
frequency light includes microwave light (radiation). This frequency light has less
energy, but it can still pop popcorn!
Unlike the wave on a rope, light does not need a medium on which to travel. Light can
travel through empty space. Light travels through empty space at a speed of almost
300,000,000 m/s. Light is an electromagnetic wave; it has electric and magnetic
properties. Light is not made by someone shaking their hand back and forth, but rather
by charges moving back and forth (accelerating).
What the different ranges of light mean
Since light can be made at various frequencies, scientists tend to group similar
frequencies together. Very high frequency light includes gamma rays and x-rays, as
shown below. Ultraviolet light is just higher in frequency than visible light. Infrared,
microwave, and radio waves have lower frequencies than visible light. The picture below
shows the ranges of light along with their relative sizes (wavelengths).
For more information . . .
1) http://imagers.gsfc.nasa.gov/ems/index.html
This is a NASA site that explains the electromagnetic spectrum. You can look at radio,
microwave, etc. and learn about the different wavelengths and their applications.
2) http://amazing-space.stsci.edu/
This site has a wonderful interactive tutorial that explores light coming from stars. Click
on “Star Light, Star Bright.” The tutorial begins with a basic explanation of waves. The
spectrum is explained using a prism. Users make their own waves by simulating a rock
dropped in a pond, a pluck of a guitar string, and light from a star. Interesting questions
are asked and answered.
http://fuse.pha.jhu.edu/~wpb/spectroscopy/basics.html
3) http://www.howstuffworks.com
This is a great website that explains how almost everything works. Since topics range
from cell phones to toilets, it’s important to search for the exact topic you want. It is
recommended that you search under topics such as “light” and “radio waves.”
1-1A
4) http://library.thinkquest.org/13405/index.html
This website explains light in more scientific detail. Topic are clearly arranged and
include the wave vs. particle model of light and color.
5) http://fuse.pha.jhu.edu/~wpb/spectroscopy/em_spec.html
A very good explanation of the electromagnetic spectrum.
6) http://fuse.pha.jhu.edu/~wpb/spectroscopy/space.html
This website explains how light is studied by breaking it its components. Specifically,
several satellite telescopes are explained.
7) http://imagers.gsfc.nasa.gov/ems/waves.html
This website has a basic description of waves—from waves in the ocean to ripples in a
flag. Then, electromagnetic waves are explained.