Question

A source produces 20 crests and 20 troughs in 0.2 second. find the frequency of the wave

Answer 1

One crest and a trough make a single wavelength.

So, 20 wavelengths are made according to the question.

Time = 0.2 seconds

Frequency = Number of waves / Time taken = 20 / 0.2 = 100 Hz

Time period = Time taken for The waves / Number of waves = 0.2 / 20 = 0.01 Second


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Answer 2

Solution :

Since the sound wave produces 20 crests in 0.2 second, the density of the medium at a place becomes maximum 20 times in 0.2 second. The number of times it becomes maximum in 1 second is

$\sf \frac{20}{0.2} \\ \\ \sf 10 \times 10 \\ \\ \sf 100$

So, the frequency is 100 times /second or 100 Hz.