Question

A source of wave produces 40 crests and 40 trough in 0.4 seconds.what is the frequency of the wave?

Answer 1

1 wavelength is 1 crest an 1 trough.
So if there are 40 crests an 40 troughs, there are 40 times wavelength.
To cover 40 wavelengths 0.4 seconds are required.
To cover 1 wavelength, 0.01 seconds are required.
Time period = 0.01 seconds
Frequency = (1/Time period) = 1÷0.01 = 100 Hz (where Hz is Hertz)

Hence the frequency of the wave is 100 Hz

Answer 2

HI !

Wavelength = 1 crest + 1 trough

Wavelength = 40 crests + 40 troughs = 40

Time = t = 0.4 sec

Frequency = Wavelength/time
= 40/0.4
= 100 Hz