3/13/12 Chapters 19-21:
Waves and Sound
Properties of Waves
•  Chapter 19: Wave Basics
•  Chapter 20: Sound Waves
•  Chapter 21: Music vs. Noise
•  Wavelength is the distance between two wave
peaks
•  Frequency is the number of times per second that
a wave vibrates up and down
wave speed = wavelength x frequency
More Wave Properties
•  Amplitude: Distance from midpoint to crest
of wave
Frequency & Period
Frequency = 1/Period
Period = 1/Frequency
They are inversely related, so they have
opposite behavior!
•  Period: Time to complete one vibration
Wavelength and Frequency
Examples:
Which wave has
the largest
wavelength?
Largest period?
Largest frequency?
Largest amplitude?
wavelength x frequency = wave speed
1 3/13/12 Types of Waves
•  Transverse Waves: like ocean waves or
waves created by shaking a string
Wave Interference
Two types of interference: constructive and
destructive.
•  Longitudinal Waves: compression waves,
such as sound
Destructive:
Slinky & string demo!
Constructive:
Standing Waves
•  When a wave is confined to a small space (such
as along a length of string), we can use
constructive interference to create a standing
wave.
The Doppler Effect
•  Definition: “The change in wavelength of
radiation due to relative radial motion
between the source and the observer.”
•  This works for either translational or longitudinal
waves!
Doppler Effect
Real Life Example of Doppler Effect
The change in the pitch of a siren on a
police car, fire truck, or ambulance as it
zooms past (sound waves)
Astronomers deal with the Doppler
Effect of light waves
2 3/13/12 Doppler Effect
•  When something which is giving off light moves
towards or away from you, the wavelength of the
emitted light is changed or shifted
Doppler Effect
•  When the source of light is moving away from
the observer the wavelength of the emitted
light will increase. We call this a “redshift”.
V=0
Star
Light Wave
Doppler Effect
•  When the source of light is moving towards
the observer the wavelength of the emitted
light will appear to decrease. We call this a
“blueshift”.
Conceptual check:
When sound waves from a police siren are
blueshifted, what property of the sound
wave is increasing?
A.  The amplitude
B.  The frequency
C.  The speed
D.  The wavelength
Doppler Effect
•  “Radial” means “along line of sight”
•  Doppler Effect happens only if the light
source is moving towards you or
away from you.
Bow Waves and Shock Waves
•  Produced by objects moving at a greater
speed than the waves they are producing.
•  Bow waves: Like boats moving faster than
the water waves
•  Shock waves: Like planes or whips
moving faster than sound waves.
•  When the shock wave reaches you, you’ll
hear it!
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