2.  The intensity of a sound is related to the amount of energy flowing in the sound waves. It depends on the amplitude of the vibrations producing the waves.

3.  The larger the amplitude of vibration is, the more intense will be the sound.

4.  The loudness of a sound refers to how strong the sound seems to us when it strikes our ears. At a given frequency, the more intense the sound is, the louder it seems.

5.  Water waves in a pond get weaker as they travel away from their source. In the same way, sound waves lose intensity as they spread outward in all direction from their source.

6.  Thus, the loudness of a sound decreases as the distance increases between a person and the source of the sound.

8.  A sound wave that is twice as loud has roughly ten times the intensity.

9.  ß (in dB) = 10 log (I/Io) b – is the loudness measured in decibels (dB) I – is the intensity of the sound wave in watt/m^2 Io – is a constant equal to 1 x 10^-12 watt/m^2

10.  Io represents the most faintly heard sound by humans and is defined as the loudness of 0 dB. Just as for gravity, electricity and magnetism, the intensity of sound drop off as the inverse square of the distance from the source.

11.  Scientist use a unit called decibel to measure the intensity level of a sound. A 3000-hertz tone of zero decibels marks the threshold of audibility- the weakest sound that the normal human ear can hear. A sound intensity level of 140 decibels is the threshold of pain.

12.  Sounds of 140 decibels or more produce pain in the ear, rather than hearing. A whisper amounts to about 20 decibels. Ordinary conversation has an intensity level of about 60ndecibels. Loud rock music can produce up to 120 decibels.

13.  The sound in a particular place has an intensity of 2.0 x 10^-7 W/m^2. what is the loudness of the sound? If the intensity is tripled, what is its corresponding loudness?  Note: Io = 1 x 10 ^-12 Watt/m^2 is the threshold audibility of human ear.

14.  Given: Sound intensity I 2.o x 10^-7 W/m^2  Find: a. Loudness (ß) at the current intensity b. Loudness (ß) if the current intensity is tripled.

15.  Solutions: a. Using the equation given. ß (in dB) = 10 log ( I/Io ) = 10 log (2.0 x 10^-7 W/m^2 / 1 x10^-12 W/m^2 = 10 log (2.0 x 10^5) = 10 (5.3) = 53 dB

16. b. When the current intensity is tripled. Using the same equation given. I = 3 (2.0 x 10^-7 W/m^2) = 6.0 x 10^-7 W/m^2 ß (in dB) = 10 log ( I/Io ) = 10 log (6.0 x 10^-7 W/m^2 / 1 x10^-12 W/m^2 = 10 log (6.0 x 10^5) = 10 (5.8) = 58 dB