11.1. Transmission of Sound http://www.ck12.org
You can experience the effect of the superposition of sound waves if you listen to music from two different sources.
Let’s use the example of two speakers. If you change your position relative to the speakers, you will notice that
there are places where the sound is louder and softer. This effect can be attributed to the distance (called the path
length) over which the sound travels from each speaker. When the sound sources are equidistant from the listener,
as inFigure11.3, or a multiple of whole-wavelengths, the superposition of the waves is constructive.But when the
path length difference between the waves is a multiple of odd half-lengths (the crest of one wave overlaps with the
trough of the other wave), the superposition of the waves is destructive,as shown inFigure11.4. We associate the
volume of the sound with the amplitude of the resultant wave. The larger the amplitude, the louder the sound.
FIGURE 11.3
Constructive interference.FIGURE 11.4
Destructive interference.http://phet.colorado.edu/en/simulation/wave-interference
http://www.youtube.com/watch?v=J_xd9hUZ2AY
Check Your Understanding
- Two waves with the same wavelength and period, but with different amplitudes of 4.0 cm and 3.0 cm interfere.
a. What is the maximum amplitude of their superposition?
Answer: The positive sum of their amplitudes is 4. 0 cm+ 3. 0 cm= 7. 0 cm.
b. What is the minimum amplitude of their superposition?