1-3
example, radio waves, such as those received by our portable radio or television sets, cannot be seen,
heard, or felt. A device must be used to convert radio waves into light (TV pictures) and sound (audio) for
us to sense them.
A WAVE can be defined as a DISTURBANCE (sound, light, radio waves) that moves through a
MEDIUM (air, water, vacuum). To help you understand what is meant by "a disturbance which moves
through a medium," picture the following illustration. You are standing in the middle of a wheat field. As
the wind blows across the field toward you, you can see the wheat stalks bending and rising as the force
of the wind moves into and across them. The wheat appears to be moving toward you, but it isn’t. Instead,
the stalks are actually moving back and forth. We can then say that the "medium" in this illustration is the
wheat and the "disturbance" is the wind moving the stalks of wheat.
WAVE MOTION can be defined as a recurring disturbance advancing through space with or without
the use of a physical medium. Wave motion, therefore, is a means of moving or transferring energy from
one point to another point. For example, when sound waves strike a microphone, sound energy is
converted into electrical energy. When light waves strike a phototransistor or radio waves strike an
antenna, they are likewise converted into electrical energy. Therefore, sound, light, and radio waves are
all forms of energy that are moved by wave motion. We will discuss sound waves, light waves, and radio
waves later.
Q2. How is a wave defined as it applies to wave propagation?
Q3. What is wave motion?
Q4. What are some examples of wave motion?
WAVE MOTION IN WATER
A type of wave motion familiar to almost everyone is the movement of waves in water. We will
explain these waves first to help you understand wave motion and the terms used to describe it.
Basic wave motion can be shown by dropping a stone into a pool of water (see figure 1-1). As the
stone enters the water, a surface disturbance is created, resulting in an expanding series of circular waves.
Figure 1-2 is a diagram of this action. View A shows the falling stone just an instant before it strikes the
water. View B shows the action taking place at the instant the stone strikes the surface, pushing the water
that is around it upward and outward. In view C, the stone has sunk deeper into the water, which has
closed violently over it causing some spray, while the leading wave has moved outward. An instant later,
the stone has sunk out of sight, leaving the water disturbed as shown in view D. Here the leading wave
has continued to move outward and is followed by a series of waves gradually diminishing in amplitude.
Meanwhile, the disturbance at the original point of contact has gradually subsided.
