PHYS 2211 Module 15.3

Sound Intensity

Recommended Reading

15.3 Sound Intensity

Learning Objectives

By the end of this section, you will be able to:

  • Define the term intensity
  • Explain the concept of sound intensity level
  • Describe how the human ear translates sound

Sound Intensity Level


Practice 15.3.1
A point source broadcasts sound into a uniform medium. If the distance from the source is tripled, how does the intensity change?
(a) It becomes one-ninth as large. 
(b) It becomes one-third as large. 
(c) It is unchanged.
(d) It becomes three times larger. 
(e) It becomes nine times larger.


A fan at a rock concert is 30 m from the stage, and at this point the sound intensity level is 110 dB. 

(a) How much energy is transferred to her eardrums (diameter = 8.4 mm)  each second?

(b) How fast would a 2.0 mg mosquito have to fly to have this much kinetic energy?

You double the intensity of a sound wave in air while leaving the frequency unchanged. (The pressure, density, and temperature of the air remain unchanged as well.) What effect does this have on the displacement amplitude, pressure amplitude, bulk modulus, sound speed, and sound intensity level?