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Sensing and Datalogging for Science Education |
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Sciencescope |
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Last updated 31st July 2008 Sensors Logbooks PriceLists Investigations 2008 Catalogue |
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Sound and ultrasoundSounds
are carried by waves. Humans
can hear sounds ranging from 20 hertz to 20 000 hertz. This is often referred to
as the range of hearing.
Not everyone can hear over all of this range - the numbers are only approximate.
In particular the high frequency limit reduces with age. The
loudness of a sound is
a measure of the amplitude
of the wave: The greater the amplitude, the louder the sound is. The
pitch of a sound is a
measure of the frequency
of the wave: the higher the frequency, the higher the pitch is. Sound
levels are measured on a scale known as the decibel (dB) scale: the higher the number the greater
the sound level is. Too
much noise can damage hearing. Exposure to 90-decibel sound levels for a long
time can cause permanent hearing loss. Exposure to a brief sound level of 140
decibels will cause pain and can cause permanent damage to hearing. Examples
of sound levels ranging from 0 decibel to 140 decibels:
Ultrasounds
are high frequency vibrations beyond the range of human hearing. The frequency
of ultrasounds is therefore greater than 20 000 hertz. Ultrasounds,
like audible sounds, are transmitted by means of waves. Ultrasound
is used in medicine to break up kidney stones and gallstones. It is also used,
in a process known as medical scanning or imaging, to create images of an unborn
baby in a womb. Medical
scanning works as follows. Ultrasound penetrates bodies well but some is
reflected off each tissue boundary. The reflected ultrasound pulses are used to
build up pictures inside the body, for example, of an unborn baby. The body
absorbs some of the energy of the wave but it is a lot less damaging than other
penetrating waves such as X-rays. You
are going to do two types of experiments:
View and/or download the worksheet View and/or download the Datadisc file examples of this investigation (you must have Datadisc installed to view the file, downloadable from Download Centre) |
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