Question

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

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

Answer 1

The correct option is C

$100Hz$

A crest is the maximum value of the wave quantity. So at the source, the wave quantity attains a maximum value of $20$ times in $0.2sec$. The number of times it becomes maximum in 1 second is $\frac{20}{0.2}=100$, which is the frequency of the wave.