Question:

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

Updated On: Aug 1, 2022
  • 12
  • zero
  • 1
  • 6
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The Correct Option is D

Solution and Explanation

Let $\lambda_{1}=5.0 \,m , v=330\, m / s$ and $\lambda_{2}=5.5\, m$ The relation between frequency, wavelength and velocity is given by $v=n \lambda \Rightarrow n=\frac{v}{\lambda} $...(i) The frequency corresponding to wavelength $\lambda_{1} . n_{1}=\frac{v}{\lambda_{1}}=\frac{330}{5.0}=66\, H z$ The frequency corresponding to wavelength $\lambda_{2}, n_{2}=\frac{v}{\lambda_{2}}=\frac{330}{5.5}=60 \,Hz$ Hence, number of beats per second $=n_{1}-n_{2}=66-60=6$
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Concepts Used:

Beats

What is Beat Frequency?

Let’s see from fig.m, the frequency of a pink-colored wave is f1, and that of a green-colored wave is f2. So, the frequency of the beat is the difference between these two, which is:

                               fBEATS  = |f1 - f2|

Interference and Beats

When two or more waves travelling in a medium meet, the resulting phenomenon is called interference and beats are an excellent example of the phenomenon of interference. 

What is Interference?

When two or more waves travelling in a medium meet, the resulting phenomenon is called interference and beats are an excellent example of the phenomenon of interference.

The Application of Beats:

  • Beats are used in determining the unknown frequency
  • Beats are used in determining the existence of poisonous gases in mines.