BACKGROUND:
There are many waves generated by the
release of energy but the two major types of waves are physical and
electromagnetic. Physical waves need a medium to go through, and
electromagnetic can go through many substances including a vacuum.
The more students review the
different types of waves, the easier it will be for them to recognize
the differences. You will be demonstrating the 2 major types of waves:
electromagnetic and physical. To illustrate this to students
explain that sound is
a physical wave, and light, microwaves, television and radio waves are
all electromagnetic.
The term "wave" refers to
both physical and electromagnetic. The different components include; the
crest (top of a wave); trough (bottom of the wave); wave height (how
high is the crest); and wavelength (distance from crest to crest or
trough to trough). These terms even apply to the waves produced in
oceans.
Waves are essentially a way in which
energy can be transferred from one place to another. These concepts will
be developed in high school physics. PROCEDURE:
 Discuss with students the components of a
wave, whether physical or electromagnetic. Go over crest, trough,
wavelength, and wave height, defined by the figure to the right.
- Explain that there are two major types of
waves, physical and electromagnetic.
Physical waves must have a medium to transfer energy, like water, a
rope, or a slinky. An electromagnetic wave can go through a vacuum,
like light or x-rays.
- Demonstrate a physical wave by using a
slinky. One student holds a slinky on one end. The teacher stretches
the slinky about 2-3 feet. The teacher will transmit energy by
pulling back several of the coils and then releasing them. The
movement will be a push-pull or compressional wave. Instruct
students to record what they see.
- Demonstrate another example of a physical
wave using a rope. Tie the rope to something stationary. From the
opposite end, one student will hold the loose end of the rope and
transmit energy by snapping his wrist toward the stationary end of
the rope. Have students record the movement of the rope. This
illustrates transverse (or shear) waves, a physical wave.
- Using an eyedropper and a pan of water, drop
water into a pan of water very slowly. Record the movement of the
water's surface. These are physical waves.
- If you have a radiometer, place it in the
sun. Record what happens. Notice that the black and white panels
move around. The electromagnetic waves of light are hitting the
white panel and pushing the panels. It also demonstrates that light
waves have a physical component, pushing is a mass effort. The mass
of the light waves reflecting from the white surface cause kinetic
energy derived from the potential energy.
- Turn a radio on, and ask students where is
the music coming from. Turn it off. Why doesn’t the room fill with
music if radio waves are all around? The radio concentrates radio
waves. Make sure the students realize that the sound produced is not
the actual radio waves.
Conclude that electromagnetic waves can travel through a vacuum
and physical waves cannot. Sound waves are visible and some
electromagnetic waves are invisible.
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