Q115 / 200 · NEET 2006 · Physics

Two sound waves with wavelengths 5.0 $\mathrm{m}$ and $5.5 \mathrm{~m}$ respectively, each propagate in a gas with velocity $330 \mathrm{~m} / \mathrm{s}$. We expect the following number of beats per second:

Correct answer
A
6
B
12
C
0
D
1

Solution

$$ \begin{gathered} \text { Frequency }=\frac{\text { Velocity }}{\text { Wave length }} \\ V_1=\frac{V}{\lambda_1}=\frac{330}{5}=66 \mathrm{H}_2 \end{gathered} $$ and $V_2=\frac{V}{\lambda_2}=\frac{330}{5 \cdot 5}=60 \mathrm{H}_2$ $\therefore$ Number of beats per second $=V_1-V_2=60-60=6$.

Hence, the correct answer is option: 'A'.

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