Traditional Indonesian music uses an ensemble called a gamelan that is based on tuned percussion instruments somewhat like gongs. In Bali, the gongs are often grouped in pairs that are slightly out of tune with each other. When both are played at once, the beat frequency lends a distinctive vibrating quality to the music. Suppose a pair of gongs are tuned to produce notes at 151 Hz and 155 Hz. How many beats are heard if the gongs are struck together and both ring for 2.5 s?
There would be 10 beats in 2.5 seconds
The frequencies at which the pair of gongs produces notes
f1= 151 Hz
Both the gongs ring for the time t = 2.5 sec
The frequency of the beats produced by the pair of gongs is given by
Thus, the frequency of the beat is 4Hz
Now, the number of beats in time t =2.5 s
Thus, there would be 10 beats in 2.5 seconds
Noise-canceling headphones are an application of destructive
interference. Each side of the headphones uses a microphone to
pick up noise, delays it slightly, then rebroadcasts the noise next
to your ear where it can interfere with the incoming sound wave
of the noise. Suppose you are sitting 1.8 m from an annoying,
110 Hz buzzing sound. What is the minimum headphone delay, in
ms, that will cancel this noise?
Two in-phase loudspeakers, which emit sound in all directions,
are sitting side by side. One of them is moved sideways by 3.0 m, then forward by 4.0 m. Afterward, constructive interference is
observed and of the distance between the speakers along the line that joins them. What is the maximum possible wavelength of the sound waves?
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