The
Characteristics of Sound and Light Waves
There
are many different kinds of waves. Waves can carry a little energy
or a lot. They can be short or long. They can be rare or frequent.
They can travel fast or slow. Sound waves, light waves, X-rays, microwaves,
and ocean waves are but a few examples. All waves, however, share
certain basic characteristics.
All waves have
amplitude, wavelength, and frequency.
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In order to understand these characteristics
of waves, it may help you to represent a wave as a drawing on a graph.
The X-axis (the horizontal line) represents the normal, or resting position.
For
example, the X-axis might represent a calm sea or a tight rope. The
vibrational movements of the wave are shown on the Y-axis. The highest
points on the graph are called peaks or crests. The lowest points
are called troughs.
Some waves are very high, while
others are barely noticeable. The distance the wave rises depends
on the amplitude of the wave. Amplitude
is the maximum distance the medium (the material through which a wave travels)
moves away from its rest position. The higher the wave moves up-and-down
as it vibrates, the larger the amplitude of the resulting waves.
The number of complete waves, or complete
cycles, per unit of time is called the frequency.
Because every complete wave has one crest and one trough, you can think
of the frequency as the number of crests or troughs produced per unit time.
The unit used to measure wave frequency is called the hertz (Hz).
The frequency of a wave depends on the frequency at which its source is
vibrating. Frequency, which is often used to describe waves, is an
important characteristic. Frequency is used to distinguish one color
of light from another, as well as one sound from another. For example,
red light is different from blue light because red light has a lower frequency.
A dog can hear a whistle that you cannot hear because dogs can hear sounds
at higher frequencies than humans can.
Properties
of Sound
There
are millions of different sounds in everyday life. Each sound having
certain characteristics that make it unique. Think about the many
sounds you hear everyday. How you hear and describe a sound depends
on the physical characteristics of the sound wave.
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Frequency
and Pitch
Certain sounds are described as high, such as those produced by a piccolo,
or low, such as those produced by a bass drum. A description of a
sound as high or low is known as the pitch
of the sound. The pitch of a sound depends on how fast the particles
of a medium (the material through which a wave travels) vibrate.
So the pitch of a sound depends on the number of waves produced in a given
time.
Key point here: Sound waves that have a high frequency are heard
as sounds of high pitch. A violin produces high-pitched sounds.
Sound waves that have a low frequency are heard as sounds of low pitch.
A tuba produces low-pitched sounds.
Frequency is an especially important characteristic of sound because the
ear can respond to only certain frequencies. The normal human ear
is capable of detecting from about 20 to 20,000 vibrations per second,
or hertz.
Here is a helpful link for more information on
sound waves: http://www.ronkurtus.com/physcien/sound.htm
Properties
of Light
What does sunlight have in common with the X-rays used in a doctor's office?
Are you surprised to learn that they are both waves? They're not
matter waves that you can hear or feel. They are electromagnetic
waves. Electromagnetic waves disturb electric and magnetic fields.
These waves can be transmitted through a vacuum (space free of particles).
They do not depend on particles of matter.
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Light
is an electromagnetic wave. Light
from the sun can travel to the Earth through the vacuum of space.
Light can also travel through air across your room. Although you
might not realize it, you are constantly surrounded by thousands of electromagnetic
waves everyday. Sunlight (visible light) and X-rays are only two
types of electromagnetic waves. Other types are radio waves, infrared
rays, ultraviolet rays, and gamma rays.
Here is a helpful link for more information on
light waves: http://junior.apk.net/~matto/notes(3).htm
by Angie Evenson, aka WAVELOVER, Concordia College, 12/6/99
Email Angie
Special thanks to Lycos picture
search for providing great information and graphics.
Concordia College, Moorhead
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