Sound Wave PDF

Sound wave Sound waves are longitudinal waves, made by particles vibrating Sound waves cannot travel in space, or vacuum. compression rarefaction distance   The medium particles oscillate backwards and forwards as the compressions and rarefac...

Sound wave Sound waves are longitudinal waves, made by particles vibrating Sound waves cannot travel in space, or vacuum. compression rarefaction distance   The medium particles oscillate backwards and forwards as the compressions and rarefactions pass through. When a compression passes, the pressure rises. When a rarefaction passes, the pressure falls.  Displacement Displacement Time Time Loudness Pitch of sound Timbre Speed  Displacement A A Time Loudness(响度) of the sound How quiet a sound is depended on the amplitude of the sound wave. The greater the amplitude of the wave the louder the sound.振幅大，声音响 Ticking of a Watch 20 db Whisper Normal Speech 30 db 50-60 db Alarm Clock Car Traffic 80 db 70 db  Displacement Time Pitch(音调) of the sound The pitch of a note depends on the frequency of the wave. The higher the frequency of the wave the higher the pitch. 频率大，音调高 27.5 Hz 4186.01 Hz Infrasound audio/sound Ultrasound 20 kHz Human ear is capable of hearing Timbre(音色)of sound The quality by which you can distinguish one sound from another  Speed of sound distance the sound wave moves per unit time v = f Sound waves travel faster in solids due to the strongest interactions between particles vsolids > vliquids > vgases  Speed of Medium sound(m/s) Rubber 60 Air at 0 oC 332 Air at 20 oC 343 Air at 40 oC 355 Lead 1210 Gold 3240 Glass 4540 Copper 4600 Aluminum 6320 What’s the wavelength of a 20 Hz note? v = f  = v / f = 340 / 20 = 17m What’s the wavelength of a 20 kHz note?  = v / f = 340 / 20000 −3 = 17 10 m = 17mm  Sound travels much more slowly than light. Two people stand at least 100 m apart, one has a starting pistol and the other a stopwatch. The person with the gun fires it and the one with the watch starts it when they see the smoke and stops it when they hear the bang. The distance between them is found and the speed of sound worked out. The experiment should be done a few times to get an average result. We will use signal generator, speaker, microphones and oscilloscope. Keep moving it until the two traces on the oscilloscope are aligned once more. We can then use the formula v = f × 𝜆 to find the speed (v) of the sound wave passing through the air — the frequency (f ) of the wave will be equal to the frequency set by the signal generator. Measuring that single short burst of time is difficult. clap repeatedly in time with the echo, so that you can only hear your own clap (the echo is masked by your next clap) So we can now measure the time it takes to clap 10 times. Start the stopwatch at the first clap and end it when you hear the echo of the 10th clap Reflection of sound 1 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 = × 𝑡𝑖𝑚𝑒 𝑟𝑒𝑐𝑒𝑖𝑣𝑒𝑑 × 𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑠𝑜𝑢𝑛𝑑 2 Uses of ultrasound Ultrasonic cleaning Echo-sounding Metal testing Scanning Uses of ultrasound ❑Ultrasonic cleaning ❑Echo-sounding ❑Metal testing ❑Scanning  True or False ❑ Sound is a longitudinal wave ❑ Sound is the vibration of matter ❑ The longer the wavelength of the wave the higher the pitch. ❑ Sound can travel in outer space ❑ Amplitude of sound corresponds to how much the wave is compressed ❑ The unit of frequency is hertz  True or false ❑ small obstacles cannot cause diffraction of wave ❑ Speed of sound depends on pressure of air ❑ Sound wave with higher frequency moving faster ❑ Different instruments have different qualities of sound ❑ Audio sound frequency range is 2 Hz to 2000 Hz