11.2 Types of Waves

A wave on a rope is an example of a transverse wave. As shown again in Figure 11.4, the motion of each individual part of the rope is perpendicular to the motion of the wave as a whole. In the figure, each piece of the rope moves up and down while the wave itself moves along from left to right. Waves on a rope or waves created in the strings of musical instruments-like a guitar, a violin, or a piano-are transverse waves. Later, when we study light we will find that light is a transverse electromagnetic wave.

Figure 11.4 In a transverse wave, the motion or disturbance of particular or individual parts of the medium that carries the wave is always perpendicular to the motion of the wave itself. In this case, the individual parts of a rope move up down while the wave as a whole moves from left to right.

A "Slinky" toy provides a good example of another kind of wave, a longitudinal wave. Figure 11.5 shows a wave moving down a Slinky. Each piece of the Slinky moves back and forth, or left and right, while the wave itself moves along from left to right. In longitudinal waves, the motion of individual pieces of the medium move back and forth along he same direction as the motion of the wave itself. Sound is another, and important, example of a longitudinal wave.

Figure11.5 A longitudinal wave can travel down a "Slinky" toy as the individual coils of the "Slinky" move back and forth.

An interesting characteristic of transverse waves is that they can be polarized while longitudinal waves can not. Figure 11.6 shows two transverse waves on a rope traveling into the page. The first one is polarized vertically; the motion of individual parts of the rope move up and down, vertically. Of course these motions are perpendicular to the motion of the wave as a whole which is into the page. The second one is polarized horizontally; the motion of individual parts of the rope move back and forth, or left and right, horizontally. Of course these motions are also perpendicular to the motion of the wave as a whole which is into the page. Since this motion is confined to a plane, these waves may be referred to a plane polarized.

Figure 11.6 A transverse wave can be polarized.

A transverse wave can be polarized by passing it through a "filter" that allows only polarized waves to pass through as sketched in Figure 11.7. There a wave on a rope arrives at a "filter" like a picket fence or the slats on the back of a kitchen chair. This filter allows only one kind of plane polarized wave to pass through while it blocks perpendicular motion. We will encounter this same type of behavior later when we talk of polarizing sunglasses in our discussion of light.

Figure 11.7 A transverse wave can be made to be polarized by passing it through a "filter" that allows only polarized waves to pass through.