2. CHAPTER 12: SOUND Sound is a longitudinal wave. Sound comes from a source, travels in a medium, as longitudinal waves, and is sensed by our ear.

3. 12-1 Characteristics of Sound Speed… sound travels in different media and temperatures at different speeds. See chart p 348 V= or use E for solids Temperature affects the speed of sound… V=(331 +.60T) m/s Loudness is related to the energy in the sound wave. Pitch of sound refers to frequency and highness or lowness of the sound.

4. Sound Characteristics (cont’d) Audible range varies with different animals… …for humans, it is about 20Hz to 20,000Hz. See conceptual example 12-1 p348 Ultrasonic sound is above 20,000Hz. Infrasonic sound is below 20Hz. See example 12-2 p349.

5. 12-2 Intensity of Sound Loudness is a sensation by humans, related to a physically measureable. The bell is the SI unit of intensity for sound… we use the dB instead because the bell is so large.( 10dB = 1B)  =10 log I/I o (where  is in dB) I o = 1.0 x 10 -12 W/m 2 …which is the threshold of perception for humans. To produce a sound that sounds twice as loud to a human requires a 10 times the intensity… I=10 -2 w/m 2 is 2X as loud as I=10 -3 w/m 2. I≈1/r 2

6. 12-3 Amplitude Related to Intensity I=P/S= 2  2 v  f 2 A 2 See example 12-5 that uses this equation.

7. 12-4 The Ear See the diagram of the ear on p353.

8. HOMEWORK!!! P375 Qustions 1,2,6 p376 pr#1-3, 5, 9-12,20- 21, 23-25 due Thursday, BOP