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CHAPTER 12: SOUND

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. 12-1 Characteristics of Sound. Speed… sound travels in different media and temperatures at different speeds. See chart p 348

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CHAPTER 12: SOUND

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  1. 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.

  2. 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.

  3. 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.

  4. 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) • b=10 log I/Io (where b is in dB) • Io = 1.0 x 10-12 W/m2 …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/m2 is 2X as loud as I=10-3 w/m2. • I≈1/r2

  5. 12-3 Amplitude Related to Intensity • I=P/S= 2p2 vrf2A2 • See example 12-5 that uses this equation.

  6. 12-4 The Ear • See the diagram of the ear on p353.

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

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