Question

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

Answer 1

One crest and one trough constitute one cycle.

40 crests and 40 troughs involve 40 cycles.

Time taken for one cycle is called time period.

So, Time period = 0.4 s / (40) = 0.01 s

Frequency = 1 / Time period
Frequency = 1 / (0.01 s) = 100 Hz.