Lesson
What is the spectrum?
77
LESSON What is the spectrum?
13
Sunlight seems to have no color at all. Yetit is really made up of every color,
from red to violet. You can see this for yourself when you see a rainbow.
During rain, there are billions of tiny water droplets in the air. When the
sun shows, they can break up sunlight into the spectrum of colors we call
the rainbow.
You can do the same thing with a glass prism. This is special glass that
breaks up light into the visible spectrum: red, orange, yellow, green, blue,
indigo, and violet. The order of the colors never changes.
When you studied sound, you learned that pitch depends on the frequency
of sound energy. Similarly,the variety of colors depends upon the frequency
of the light energy. Each color in the visible spectrum has a different
frequency of vibration. Red light has the lowest frequency. As you go from
red to violet, frequency increases.
Visible light is just a small part of a broad spectrum of energy. This energy
spectrum is called the electromagnetic [ih-LEK-tro-mag-NET-ik]spectrum,
or E-M spectrum, for short. The other parts of the E-Mspectrum are shown
in Figure C on page 81. They include radio waves, microwaves, infrared [infruh-RED] waves, ultraviolet rays, x-rays, gamma rays, and cosmic rays.
Notice where visible light fits into the E-M family.
78
UNDERSTANDING
THE VISIBLE SPECTRUM
Only the visible part of the electromagnetic spectrum vibrates at frequencies that the human
eye can sense. Each color has its own frequency.
Study Figure A. Then answer the questions.
,
.
Figure A
1. What kind of light is entering the prism?
2. The prism is _---::-__
---:-__
_
the light.
reflecting, refracting
3. The light is breaking up. It is separating into a rainbow of colors. What do we call this
rainbow of colors?
..::___----'-.::_:__
4. Which color is refracted the most?
_
5. Which color is refracted the least?
6. Which color vibrates the fastest?
7. Which color vibrates the slowest?
_
_
_;___;;_ _
79
FILL IN THE BLANK
Complete each statement using a term or terms from the list below. Write your answers in the spaces
provided. Some words may be used more than once.
visible spectrum
violet
many
orange
blue
red
green
prism
1. White light is really made up of
yellow
how fast
indigo
-'-
colors.
2. The colors that make up light are called the
~~
_
3. The colors of the visible spectrum in order are
4. Color depends upon
light energy vibrates.
5. The color that vibrates the fastest is
In Figure B, light is passing through two
white light
1. What kind of light do you think is
coming out of the prism on the right?
_
Figure B
. 80
~
_
REACHING OUT
prisms. Theyare facingin oppositedirections.
I
_
7. We can separate the colors of light with a
I
t
~
_
6. The color that vibrates the slowest is
2. What does this prove? _- ~
_
)
UNDERSTANDING
THE ELECTROMAGNETIC
SPECTRUM
Each kind of electromagnetic energy vibrates at a different frequency.As you move from left
to right in the diagram below, the frequency of vibration increases. The wavelength decreases
as you move from left to right.
Our eyes cannot see most parts of the E-M spectrum. But some parts that we cannot see do
affect the human body. Infrared energy is the heat we feel from the sun or any hot object. A
small amount of ultraviolet energy is healthy for most plants and animals, including humans.
But too much ultraviolet can be harmful. Ultraviolet rays can give us sunburn, for example.
radio waves
microwaves
infrared
waves
ultraviolet
waves
x-rays
gamma rays cosmic waves
frequency of vibrations increases
Figure C
1. The members of the electromagnetic spectrum vibrate
at one speed, at different speeds
2. The farther to the right you go on the electromagnetic spectrum, the
_________
the waves vibrate.
faster, slower
3. Which vibrate faster:
a) gamma rays or radio waves?
_--->
b) ultraviolet rays or x-rays?
""-__
~
_
c) infrared waves or cosmic rays?
d) visible light or microwaves?
4. Violet
---
"--__
_
be seen. But ultraviolet
5. Red
be seen.
can, cannot
can, cannot
be seen. But infrared
can, cannot
be seen.
can, cannot
81
TRUE OR FALSE
In the space provided, write "true" if the sentence is true. Write 'false" if the sentence is false.
1. Visible light is part of the electromagnetic spectrum.
2. Visible light takes up only a small part of the electromagnetic spectrum.
3. Every member of the electromagnetic spectrum vibrates at the same
speed.
4. We can see every member of the electromagnetic spectrum.
5. We can see ultraviolet light.
6. We can see infrared light.
7. Ultraviolet light vibrates too quickly for us to see it.
8. Infrared light vibrates too quickly for us to see it.
9. Infrared rays are heat rays.
10. The sun gives off ultraviolet and infrared energy.