sound ap physics chapter 12. 12.1 characteristics of sound vibration and waves

Sound

AP Physics

Chapter 12

12.1 Characteristics of Sound

Vibration and Waves

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

12.115.273

5.331 Ks

Tv

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 hearing12.1

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

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

A

PI

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 12.2

0

log10I

I

Source of Sound Sound Level(dB)

Jet Plane at 30 m 140

Threshold of Pain 120

Loud Rock Concert 120

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 0

12.3 The Ear

Vibration and Waves

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

Vibrations in strings

Fundamental frequency

Next Harmonic

12.4

L2L

vf

21

LL

vf 2

12 2 ff

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

L32

L

vf

323 13 3 ff

12.4 Sources of Sound: Strings and Air Columns

Vibrations in an open ended tube (both ends)

Fundamental frequency

Next Harmonic

12.4

L2L

vf

21

LL

vf 2

12 2 ff

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

12.4

L32

L

vf

323 13 3 ff

12.4 Sources of Sound: Strings and Air Columns

Vibrations in an closed end tube (one end)

Fundamental frequency

Next Harmonic

12.4

L4L

vf

41

L34

L

vf

343 13 3 ff

12.4 Sources of Sound: Strings and Air Columns

Vibrations in open ended tubes

Next Harmonic

Closed end tubes produce only odd harmonics

12.4

L54

L

vf

545 15 5 ff

12.6 Interference of Sound Waves; Beats

Vibration and Waves

12.6 Inteference of Sound Waves; Beats

If waves are produced by two identical sources

A pattern of constructive and destructive interference forms

12.6

Applet

12.7 The Doppler Effect

Vibration and Waves

12.7 The Doppler Effect

12.7