Question

Ans.
5. A source of wave produces 40 crests and 40 troughs
in 0.4 s. What is the frequency of the wave ?
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Answer 1

Answer:

Crest is a point of a wave where the displacement of swaying particles become maximum and Trough is a point of wave where displacement of swaying particles is minimum. The wave length is the distance between two closest crests or the distance between the two closest troughs. As we see 2 crests are related with one wavelength and 2 troughs are related with one wavelength. So if 40 crests and 40 troughs are there it means there are 40 wavelengths.

If 40 wavelengths produced in 0.4 seconds, then, 40 m/0.4 s wavelengths are produced in 1 second. Wavelengths produced per second is the frequency of the specific wave.

So the frequency of the sound is = 40 m/0.4 s = 100 Hz.

Answer 2

Answer:

100 Hz

Step-by-step explanation:

time period = 0.4s/40

                   = 1/100

frequency = 1/time period

∴ frequency = 100 Hz