Question

A source of sound $S$ and a detector $D$ are placed at some distance from one another. A big cardboard is placed near the detector and perpendicular to the line $SD$ as shown in figure. It is gradually moved away and it is found that the intensity changes from a maximum to a minimum as the board is moved through a distance of $20cm$. Find the frequency of the sound emitted. Velocity of sound in air is $336m/s$.

Answer 1

According to the given data

The speed of the sound in air is $V=336m/s$

The distance between maximum and minimum intensity is $\lambda /4=\left(20cm\right)$

$\Rightarrow \lambda =80cm$

Now, the frequency can be obtained as:

$\Rightarrow n=frequency=\frac{V}{\lambda }$

$=\frac{336}{80\times {10}^{-2}}=420Hz$.