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5 Acoustics in Biology and Medicine
5.18 If the absorptivity of muscle tissue is 1.2 dB/cm/MHz, how far will an
ultrasonic wave of frequency 3.4 MHz travel in that tissue before its intensity is
reduced to one fourth of its original intensity
5.19 If all the sound energy of a 1 MHz ultrasonic continuous emitter with an
intensity of 1 W/cm 2 is deposited into an isolated cubic centimeter of tissue, with
specific heat of 1.2 calories per g-degree and sound velocity of 1.54 m/s, how much
would the tissue rise in temperature after 1 min?
5.20 If a room of volume 800 m 3 were filled with noise at 40 dB level, and all the
energy of this sound goes into heating the air each quarter second, how much heat
would be produced each hour?
5.21 From the size of an African elephant’s external ear, estimate the frequency
that the elephant might be able to efficiently detect if the whole external ear vibrates
with half a wavelength across its diameter.
5.22 Sonic booms are a hazard to animals. Why are sonic booms called shock
waves? Do they shock animals?
5.23 What power (in watts) do you generate in sound if you yell to produce
an average sound of 90 dB 1 m from your mouth emitted into a solid angle of
7.3 steradians?
5.24 What are the dominant sound frequencies of: (a) the human male voice; (b)
the human female voice; (c) an orchestra playing Beethoven?
5.25 List all these physical characteristics which determine how you sound when
you speak, that allows others to identify you. Now list the important factors which
make how your voice sounds to yourself different than how others hear you.
5.26 Why do you sound like Mickey Mouse when you speak after inhaling helium
gas? (Caution: You can easily faint from lack of oxygen if you breathe helium for
more than a few tens of seconds. Without excess carbon dioxide, your brain does
not get the normal signal it uses to alert the body to gag.)
5.27 What is the amplitude of air movement with a sound of 115 dB and a
frequency of 256 Hz?
5.28 What is the wavelength in air of the highest frequency of sound you can hear?
5.29 If sound of frequency 1000 Hz is attenuated by 0.005 dB/m in 50% humidity
air, by what factor does the intensity of this should drop at a distance of 20 m,
assuming the sound is 60 dB measured 1 m from the source and spreads out
spherically?
5.30 How much energy arrives at your eardrum per second with an area of 0.2 cm 2
when a sound of level 85 dB enters the ear?
5.31 If the sound of your voice is attenuated by 0.03 dB per 100 m of damp air, by
what factor does the intensity of your voice drop at a distance of 10 m, assuming the
5 Acoustics in Biology and Medicine
5.18 If the absorptivity of muscle tissue is 1.2 dB/cm/MHz, how far will an
ultrasonic wave of frequency 3.4 MHz travel in that tissue before its intensity is
reduced to one fourth of its original intensity
5.19 If all the sound energy of a 1 MHz ultrasonic continuous emitter with an
intensity of 1 W/cm 2 is deposited into an isolated cubic centimeter of tissue, with
specific heat of 1.2 calories per g-degree and sound velocity of 1.54 m/s, how much
would the tissue rise in temperature after 1 min?
5.20 If a room of volume 800 m 3 were filled with noise at 40 dB level, and all the
energy of this sound goes into heating the air each quarter second, how much heat
would be produced each hour?
5.21 From the size of an African elephant’s external ear, estimate the frequency
that the elephant might be able to efficiently detect if the whole external ear vibrates
with half a wavelength across its diameter.
5.22 Sonic booms are a hazard to animals. Why are sonic booms called shock
waves? Do they shock animals?
5.23 What power (in watts) do you generate in sound if you yell to produce
an average sound of 90 dB 1 m from your mouth emitted into a solid angle of
7.3 steradians?
5.24 What are the dominant sound frequencies of: (a) the human male voice; (b)
the human female voice; (c) an orchestra playing Beethoven?
5.25 List all these physical characteristics which determine how you sound when
you speak, that allows others to identify you. Now list the important factors which
make how your voice sounds to yourself different than how others hear you.
5.26 Why do you sound like Mickey Mouse when you speak after inhaling helium
gas? (Caution: You can easily faint from lack of oxygen if you breathe helium for
more than a few tens of seconds. Without excess carbon dioxide, your brain does
not get the normal signal it uses to alert the body to gag.)
5.27 What is the amplitude of air movement with a sound of 115 dB and a
frequency of 256 Hz?
5.28 What is the wavelength in air of the highest frequency of sound you can hear?
5.29 If sound of frequency 1000 Hz is attenuated by 0.005 dB/m in 50% humidity
air, by what factor does the intensity of this should drop at a distance of 20 m,
assuming the sound is 60 dB measured 1 m from the source and spreads out
spherically?
5.30 How much energy arrives at your eardrum per second with an area of 0.2 cm 2
when a sound of level 85 dB enters the ear?
5.31 If the sound of your voice is attenuated by 0.03 dB per 100 m of damp air, by
what factor does the intensity of your voice drop at a distance of 10 m, assuming the