Question

A source of wave produces 20 crests and 20 troughs in 0.2s . Find the frequency of the wave

Answer 1

The distance between two successive crests or troughs is known as wavelength so wavelength=100cm .(because distance between crest & trough is 50cm)in 0.2 second,it complete 20 wave in 1 second,it will complete 20*5=100 crests.so frequency is 100 Hz

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.