Question

A source of wave produces 40 crests and 40 troughs in 0.4sec.What is frequency of wave?
ans = 100hz

Answer 1

Time period of the wave = 0.4/40 = 0.01 seconds

We know that,
Frequency = 1/ time period = 1/0.01 = 100 Hz

Answer 2

1 trough and 1 crest is produced in  0.4 / 40 = 0.01 sec.
so Time period = T = 0.01 sec
Frequency = f = 1/T = 100 Hz