Sound AP Physics Chapter 12

12.1 Characteristics of Sound Vibration and Waves 12.1 Characteristics of Sound

12.1 Characteristic of Sound Sound is a longitudinal wave Caused by the vibration of a medium The speed of sound depends on the medium it is in, and the temperature For air, it is calculated as 12.1

12.1 Characteristic of Sound Loudness – sensation of intensity Pitch – sensation of frequency Range of human hearing – 20Hz to 20,000 Hz ultrasonic – higher than human hearing dogs hear to 50,000 Hz, bats to 100,000 Hz infrasonic – lower than human hearing 12.1

12.1 Characteristic of Sound Often called pressure waves Vibration produces areas of higher pressure These changes in pressure are recorded by the ear drum 12.1

12.2 Intensity of Sound: Decibels Vibration and Waves 12.2 Intensity of Sound: Decibels

12.2 Intensity of Sound: Decibels Loudness – sensation Relative to surrounding and intensity Intensity – power per unit area Humans can detect intensities as low as 10-12 W/m2 The threshold of pain is 1 W/m2 12.2

12.2 Intensity of Sound: Decibels Sound intensity is usually measured in decibels (dB) Sound level is given as I – intensity of the sound I0 – threshold of hearing (10-12 W/m2) – sound level in dB Some common relative intensities Source of Sound Sound Level (dB) Jet Plane at 30 m 140 Threshold of Pain 120 Loud Rock Concert Siren at 30 m 100 Auto Interior at 90 km/h 75 Busy Street Traffic 70 Conversation at 0.50 m 65 Quiet Radio 40 Whisper 20 Rustle of Leaves 10 Threshold of Hearing 12.2

Vibration and Waves 12.3 The Ear

Steps in sound transmission 12.3 The Ear Steps in sound transmission 12.3

12.4 Sources of Sound: Strings and Air Columns Vibration and Waves 12.4 Sources of Sound: Strings and Air Columns

12.4 Sources of Sound: Strings and Air Columns Vibrations in strings Fundamental frequency Next Harmonic 12.4

12.4 Sources of Sound: Strings and Air Columns Vibrations in strings Next Harmonic Strings produce all harmonics – all whole number multiples of the fundamental frequency 12.4

12.4 Sources of Sound: Strings and Air Columns Vibrations in an open ended tube (both ends) Fundamental frequency Next Harmonic (These are graphs of air displacement, pressure graphs would show the opposite, eg low pressure at the opening) 12.4

12.4 Sources of Sound: Strings and Air Columns Vibrations in open ended tubes Next Harmonic Open ended tubes produce all harmonics – all whole number multiples of the fundamental frequency Examples include organ pipes and flutes 12.4

12.4 Sources of Sound: Strings and Air Columns Vibrations in an closed end tube (one end) Fundamental frequency Next Harmonic 12.4

12.4 Sources of Sound: Strings and Air Columns Vibrations in open ended tubes Next Harmonic Closed end tubes produce only odd harmonics Examples include reeded instruments and brass instruments 12.4

12.6 Interference of Sound Waves; Beats Vibration and Waves 12.6 Interference of Sound Waves; Beats

12.6 Inteference of Sound Waves; Beats If waves are produced by two identical sources A pattern of constructive and destructive interference forms Applet 12.6

12.6 Inteference of Sound Waves; Beats path length difference If the path length difference is = a whole number multiple of the wavelength, constructive interference occurs. If the pld is = ½, 1 ½, 2 ½, … times the wavelength, destructive interference occurs. 12.6

Vibration and Waves 12.7 The Doppler Effect

Doppler Effect 12.7 The Doppler Effect For a source moving towards a stationary observer: 𝑓 ′ = 𝑓 1− 𝑣 𝑠𝑜𝑢𝑟𝑐𝑒 𝑣 𝑠𝑜𝑢𝑛𝑑 For a source moving away from a stationary observer: 𝑓 ′ = 𝑓 1+ 𝑣 𝑠𝑜𝑢𝑟𝑐𝑒 𝑣 𝑠𝑜𝑢𝑛𝑑 12.7