Question

Source produces 40 crests and 40 troughs in 1 second so find frequency and time period

Answer 1

time (t)= 1sec
Wave = 40
Time period = 1/40
Frequency = 1/T
Frequency = 40Hz
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Answer 2

40 crests and 40 troughs make 40 waves.
time taken by 40 waves = 1 sec
time period of 1 wave is 1/40
Therefore time period = 0.025 sec
Now frequency= 1/0.025
= 40