Chapter 12

Chapter 12 - Chapter12 Sound TheOriginofSound

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    Chapter 12 Sound
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The Origin of Sound Sound is a longitudinal, mechanical wave.   You can hear sound with a frequency of 20  – 20,000 Hz.  Under 20 hz is infrasonic,  and above 20,000 hz is ultrasonic. We talk about the frequency of sound when  it is produced, and the pitch of sound when  we hear it.
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The Speed of Sound The speed of sound depends upon the  media in which it travels. The speed of sound in air is 331 m/s at 0°  Centigrade.   V = 331 + (0.6 m/s/°C)T The speed of sound increases by 0.6 m/s  for every 1°C increase in temperature in  air.
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Loudness When a sound is produced it has a certain  intensity.  This is defined as: I = Power/Area Area of the surface of a sphere 4 πr 2 Or intensity is measured as the ratio of power  divided by the area when the sound is produced. Loudness is a sensation when we hear a sound.   Different people react differently to the same  intensity.  In other words the same level of sound  has a different “loudness” to different people.
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Intensity of sound, (I),  is measured in W/m 2 .  However we  often measure the loudness of a sound using a scale of  relative intensity , known as the decibel (dB).   Decibels are a logarithmic scale which compares the intensity  of a sound to the intensity of sound at the  Threshold of  Hearing,  approximately 10 -12  W/m 2 . Hence the equation for calculating relative intensity is: 
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Chapter 12 - Chapter12 Sound TheOriginofSound

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