Ultrasound

The sound wave which has the frequency greater then 20khz i.e beyond the audible region is called the untrasound. The sound wave which has frequency less than 20hz are known as infrasonic sound wave or infrasound.

Production of ultrasound
1) Piezo electric method
When a force is applied into a pair faces of quartz crystal then an electric potential will be setup into the opposite pair faces. Conversly, if an electric potential be applied on a pair of quartz crystal then there will be tension on the opposite faces. This effect in quartz crystal is known as piezo electric effect.

Now When an alternating potential be applied on a pair forces of a quartz crystal then opposite force will be in longitidunal vibration when freq. of applied potential becomes equal to natural frequency of quartz crystal then resonance will occur. In that case crystal will vibrate with maximum amplitude and a sound wave will be produced with ultrasound properties.

2) Magnetic striction method
In this method a ferromagnetic material is wounded closely by a coil and alternating current is passed through it. Then we may experience a longitudinal vibration in the ferromagnetic substance. When the frequency of the alternating current becomes equal to the natural frequency of ferromagnetc substance then resonance will occur and the material will vibrate with maximum amplitude. And a sound wave is generated with unltasound Properties.

Use of ultrasound
1) To find the depth of Seas
2) To locate distance object
3) To kill unwanted tissue(blood less surgery)

Characterstics of Sound
1) Pitch: Pitch is a characterstics of sound which directly related with frequency. Sound wave having high frequency is called high pitched sound and vice versa.
2) Intensity: Sound energy flowing per unit area per unit time is called intensity
3) Threshold frequency of hearing: The minimum value of sound intensity that can be heared by human being in general
4) Loudness: It is the magnitue of sensation of hearing and it is directly proportional to the logarithm of intensity of sound
5) Quality: Quality of sound depends on no. of harmonics presents in sound. HIgher no. of harmonic reveals high quality and vice versa.