10-04-2017, 07:51 PM
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This article is presented by:
ABDUL JABBAR
MUHAMMAD MOHSIN ALI
INTRODUCTION
Sound waves in air are longitudinal waves. The disturbance that propagates in air is a change in the local air pressure (or equivalently density) above or below the average pressure
a region of higher air pressure in the wave is called a condensation, while a region of lower air pressure is called a rarefaction
The speed of sound in air depends on several factors, including the air temperature and pressure. At room temperature and standard atmospheric pressure, the speed of sound is 343 m/s.
Note that the atoms in the air do not move with the velocity v of the sound wave they just vibrate back and forth as the wave passes
INTENSITY I
the intensity I of a sound wave is defined to be the power P (work/time) carried by the wave divided by the surface area A through which the wave passes the SI unit of intensity is therefore W/m2
CALCULATING DECIBELS
The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power) relative to a specified or implied reference level. Its logarithmic nature allows very large or very small ratios to be represented by a convenient number, in a similar manner to scientific notation. Being essentially a ratio, it is a dimensionless unit. Decibels are useful for a wide variety of measurements in acoustics, physics, electronics and other disciplines.
Generally for every factor of 10 change in intensity or dB, there is a factor of 2 change in loudness
dB=10log10 (Is/Io)
Is= The intensity of the sound
Io= Hearing threshold 1x10-12 W/m2