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.


Given:
Velocity of sound in air



Distance between maximum and minimum intensity:





Frequency of sound



As we know,





Therefore, the frequency of the sound emitted from the source is 420 Hz.


1