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 (16-E1). 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 20 cm. Find the frequency of the sound emitted. Velocity of sound in air is 336 m/s.

Answer 1

According to the given data, $V=336m/s\frac{\lambda }{4}$=distance between maximum and minimum intensity =20 cm

$\Rightarrow \lambda =80cm$

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

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