Sound of Class 9

A longitudinal wave whose frequency is above the upper limit of audible range i.e. 20 kHz, is called ultrasonic wave. it is generated by very small sources.

e.g.Quarts crystal.


Sound of very high frequency (greater than 20 kHz) is called ultrasound.

Production :

These are produced by electric oscillator using high frequency vibrations of quarts crystal.

Properties :

Sound wave of all frequencies carry energy with them, with increase in frequency, vibration becomes faster and both energy and force increase. When ultrasound travels in solid, liquid and gas it subjects the particles of matter to face large force and energy.


In contrary to audible sounds (which have lower frequencies), ultrasound can be obtained in the form of a narrow beam which can travel along well-defined paths even in the presence of obstacles. Such well-defined narrow beams of ultrasonic waves find application in many fields. 

  • Industry
  •  Medical science 
  •  Communication (SONAR)

Industrial uses of ultrasound:

The various uses of ultrasound in industries are as follows :

  • Cleaning instruments and electronic components :The cleaning is done by the method called cavitation or coldboiling. An instrument that needs cleaning but whose parts cannot be reached directly is placed in a liquid. The ultrasonic waves passing through the liquid produce tiny bubbles where the rarefaction of the ultrasonic wave reaches. When the compression of the wave reaches these bubbles, the bubbles are compressed until they implode (explode inward). This leads to the creation of several small localized shockwaves. These shock waves blast away any dirt or contamination from the unreachable portions, usually, frequencies in the range of 20 kHz to 30 kHz are used for this purpose.
  • Plastic welding :Application of small pressures and ultrasonic vibration to two similar surfaces produce sufficient thermal energy to bond the surface together.
  • Detecting flaws and cracks in metal blocks : To construct big structures like buildings, bridges, machines and scientific equipment, a large number of metallic blocks are assembled together. Cracks and holes within the blocks, which are invisible from outside, reduce the strength of a structure. To detect these flaws (cracks and holes) in a block, ultrasonic waves are passed through it.


Medical uses of ultrasound:

  •  Echocardiography :It is used to study the heart-valve action. An image of the heart is obtained by getting ultrasonic waves reflected from various parts of the heart.
  • Ultrasonography : It involves sending ultrasonic waves to various organs (like brain, liver, kidneys) in the body and looking at the reflected or transmitted waves. Using ultrasonography, stones in gall-bladder and kidneys or tumors in different organs can be detected. Ultrasonography is also used in prenatal examinations. 
  • Therapeutic uses :Ultrasound is used for treatment of neuralgic and rheumatic pains.
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