Wave motion

One of the most important phenomena in nature is the transmission of energy from one point to another by wave motion. When you drop a stone into a pool of still water, the surface of the water is soon covered with circular waves.

Fig. 15

The water does not really move from the central point but it rises and falls again. Motions of this kind are wave motion.

We can see water waves almost every day. We make use of light waves to see the water waves and we hear sounds by means of sound waves. All wave motions possess three characteristics:

1) amplitude, which is the height or strength of the wave;

2) frequency, the number of waves per second;

and 3) wavelength, the distance from the crest of one wave to the crest of the next.

Sound waves are produced by vibrations. Sound waves travel through the air at a speed of about 1,100 ft. per second.

The microphone, the loudspeaker and headphones are devices used in transmitting sound (Fig. 15).

To find the velocity (or the speed) of the wave motion we multiply the frequency by the wavelength:

v= fl

where f stands for frequency,

l stands for wavelength,

v stands for velocity.

This important equation is true for electric waves as well as for sound waves.

Radio waves are electric waves of very high frequency; they travel through space with the speed of light. They differ from other wave forms, such as light waves, heat sec

Fig. 16

fig. 17

waves or X-rays, only in frequency (number of vibrations second).

Figure 17 shows waves being sent out in all directions from a transmitting tenna.

UNIT I

WHAT IS PHYSICS?