同济大学：《大学物理》课程教学资源（电子教案，英文版）第九章 机械波（下）

Sound waves

Sound waves

Agenda today 1.The Speed of Sound Waves 2.Interference of sound waves 3.Doppler effect

Agenda today 1. The Speed of Sound Waves 2. Interference of sound waves 3. Doppler effect

Sound waves: Frequency of sound waves(pitch):20--25000 Hz The intensity of sound waves: Decibel scale B=101og70 =10-12W/m2 Business office Heavy truck Jet take-off 50 6) Loudness (dB)

Sound waves: Frequency of sound waves(pitch): 20--25000 Hz The intensity of sound waves: Decibel scale I0=10-12 W/m2

Hammer Anvil Stirrup Semicircular canals (for balance) Oval window 八 Vestibular nerve Cochlear nerve Cochlea / Eardrum (tympanum) Eustachian tube ”% Ear canal W Harmonic Decay=1/k(k odd)

white noise High pass Pink noise Low pass Band pass

white noise High pass Low pass Band pass Pink noise

Attenuation of sound waves A=Ao -0X -20x

Attenuation of sound waves x A A e   0 x I I e 2 0  

Receiver Transmiter Reflected Transmitted pulse pulse To measure the depth of water Why is sonar used to measure the depth of water not radar?

Why is sonar used to measure the depth of water not radar?

The Speed of Sound Waves 0 dx F=pA-(p+△p)A F=△ma=pA△x △V =-△pA △t △P △P B △ △N

The Speed of Sound Waves o x x dx  B v 

The interference of Sound Waves Two loudspeakers,Sl and S2,are separated by 0.50 m.These speakers form sound waves of the same amplitude at a frequency of 4400 Hz.The amplifier emits the two waves 180 degrees out of phase.A set of chairs is arranged in a semicircle 30.0 m from the midpoint of the two speakers. Find the amplitude of the wave at the chair on the perpendicular bisector (center line)of the line between the speakers.At what distance to the right of this central chair is there a first maximum in sound intensity? 51 52 快 明 Le

The interference of Sound Waves Two loudspeakers, Sl and S2, are separated by 0.50 m. These speakers form sound waves of the same amplitude at a frequency of 4400 Hz. The amplifier emits the two waves 180 degrees out of phase. A set of chairs is arranged in a semicircle 30.0 m from the midpoint of the two speakers. Find the amplitude of the wave at the chair on the perpendicular bisector (center line) of the line between the speakers. At what distance to the right of this central chair is there a first maximum in sound intensity?

Beats

Beats