Sound waves are longitudinal mechanical waves.
According to their frequency range, longitudinal mechanical
waves are divided into the following categories:
Audible
or Sound waves: The longitudinal mechanical waves which lie in the
frequency range 20 Hz to 20000 Hz are called audible or sound waves. These waves
are sensitive to human ear. These are generated by the vibrating bodies such as
tuning fork, vocal cords etc.
Infrasonic
waves: the longitudinal mechanical waves having frequencies of bigger size
such as earth quakes, volcanic eruptions, ocean waves and by elephants and
whales.
Ultrasonic
Waves: The longitudinal mechanical waves having frequencies greater than 20000
Hz are called ultrasonic waves. Human ear cannot detect these waves. But
certain creatures like dog, cat, bat, and mosquito can detect these waves. Bat
not only detect but also produce ultrasonic.
Ultrasonic waves can be produced by Galton’s
whistle or Hartman’s generator or by the high frequency vibrations of a quartz
crystal under an alternating electric field (Piezo- electric effect) or by the
vibrations of a ferromagnetic rod under an alternating magnetic field (Magnetostriction).
Applications
of Ultrasonic Waves
1.
For sending signals.
2.
For measuring the depth of sea.
3.
For cleaning cloths, aero planes and machinery
parts of clocks.
4.
For removing lamp-shoot from the chimney of
factories.
5.
In sterilizing of a liquid.
6.
In Ultrasonography.
