Solved Example Problems for Intensity and Loudness of sound

EXAMPLE 11.23

A baby cries on seeing a dog and the cry is detected at a distance of 3.0 m such that the intensity of sound at this distance is 10-2 W m-2. Calculate the intensity of the baby’s cry at a distance 6.0 m.

Solution

I1 is the intensity of sound detected at a distance 3.0 m and it is given as 10-2 W m-2. Let I2 be the intensity of sound detected at a distance 6.0 m. Then,

 r1 = 3.0 m,

r2 = 6.0 m

the power output does not depend on the observer and depends on the baby. Therefore,

I2 = 0.25 × 10-2 W m-2

EXAMPLE 11.24

The sound level from a musical instrument playing is 50 dB. If three identical musical instruments are played together then compute the total intensity. The intensity of the sound from each instrument is 10-12 Wm-2

Solution

I1 = 10-7 Wm-2

Since three musical instruments are played, therefore, Itotal = 3I1 = 3 × 10-7 Wm-2.