Question

Which of the following correctly represent schematically, the wave pattern produced by superposition of two waves of frequencies $9\text{Hz}$ and $11\text{Hz}$ is

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

We know that , when waves of nearby frequencies overlaps, beats are produced.

Beat frequency, $f_B=|f_1-f_2|$

$\Rightarrow f_B=11-9=2\text{Hz}$

So, time period, $T_B=\frac{1}{f_B}$

$\Rightarrow T_B=\frac{1}{2}=0.5\text{s}$

So, resultant wave has a time period of $0.5\text{s}$.

For graph of option A, the time period is $0.5\text{s}$

Hence, option $\left(a\right)$ is correct.

Why this question ? This question provides understanding of graph for superposition of two waves.