Question

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

• A. $200Hz$
• B. $500Hz$
• C. $100Hz$
• D. $300Hz$

Answer 1

The correct option is C $100Hz$

A crest and a trough makes up for one oscillation.
So, 20 crests and 20 troughs together make 20 oscillations.
Given that the time taken for 20 oscillations is 0.2 seconds.
Frequency ($f$) of a wave is the number of oscillations made in one second.
$f=\frac{20}{0.2}=\frac{200}{2}=100$
Frequency $=100Hz$