Lecture 14: Waves and Sounds Ch 16

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Lecture 14 Waves and Sounds (Ch 16)
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Nature of Waves
Transverse Wave
Longitudinal Wave
Sound
Radio waves, Light, Microwaves
Acoustics and Vibration Animations - Dan Russell,
Kettering University
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Periodic Waves
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Speed of a Wave
Example 2 Transverse waves travel on the strings
of an electric guitar after the strings are
plucked (see Figure). The length of each string
between its two fixed ends is 0.628m, and the
mass is 0.208 g for the highest pitched E string
and 3.32 g for the lowest pitched E string. Each
string is under a tension of 226 N. Find the
speeds of the waves on the two strings.
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Mathematical Description of a Wave
Phase Angle
These equations apply to transverse or
longitudinal waves and assume that y 0 m when x
0 m and t 0 s.
The quantity x/v is the time needed for the wave
to travel the distance x.
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Nature of Sound Waves
Sound Waves are LONGITUDINAL WAVES
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Nature of Sound Waves
Frequency of Sound wave
Each cycle of a sound wave includes one
condensation and one rarefaction, and the
frequency is the number of cycles per second that
passes by a given location. A sound with a
single frequency is called a pure tone.
Sound can be generated whose frequency lies below
20 Hz or above 20 kHz, although humans normally
do not hear it. Sound waves with frequencies
below 20 Hz are said to be infrasonic, while
those with frequencies above 20 kHz are referred
to as ultrasonic. Pitch A pure tone with large
frequency is a high pitched sound
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Nature of Sound Waves
Pressure Amplitude of Sound Wave
Loudness depends on the amplitude of the wave.
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Speed of Sound
Bad Adiabatic Bulk Modulus Y Youngs Modulus
Air (0 deg) 330 m/s Air (20 deg) 343
m/s Mercury 1450 m/s Steel 5960 m/s
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Sound Intensity
The unit of sound intensity is power per unit
area, or W/m2.
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Decibels
The decibel (dB) is a measurement unit used when
comparing two sound intensities.

• Threshold of hearing 0 dB
• Normal Conversation 65 dB
• Inside Car 80 dB
• Live rock Concert 100dB
• Pain 130 dB

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Doppler Effect
The Doppler Effect and Sonic Booms - Dan Russell,
Kettering University
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Doppler Effect
MOVING OBSERVER
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Applications of Sound in Medicine
Doppler Flow Meter
CUSA probe
Ultrasound

• Malignancies in the liver, kidney, brain, and
  pancreas can be detected with ultrasound.
• The wavelength of the sound wave must be about
  the same size as, or smaller than, the object to
  be located.
• Neurosurgeons use a device called a cavitron
  ultrasonic surgical aspirator (CUSA) to remove
  brain tumors.
• Doppler flow meters for measuring speed of
  blood flow.