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Sounds are of different frequencies, but not all the sounds are being heard by human beings. Sounds are of two types.
  • Audible sound
  • Inaudible sound
Audible sound:
  • Sounds, which can be heard by us, are called audible sounds.
  • Human beings can hear sound having a frequency from \(20\) \(Hz\) to \(20,000\) \(Hz\).
Inaudible sound:
  • Sounds, which cannot be heard by us, are called inaudible sounds.
  • Human beings cannot hear sound having a frequency less than \( 20\) \(Hz\)  or more than \(20,000\) \(Hz\).
The sounds that have a frequency range below \(20\) \(Hz\) is called infrasound. Infrasound is employed in the earth monitoring system. It is also used in the study of the mechanism of the human heart.The sound waves that have a frequency range above \(20,000 \) \(Hz\) are called ultrasounds.
If we could hear infrasound, we would hear the vibrations of a pendulum. Rhinoceroses communicate using infrasound of frequency as low as \(5\) \(Hz\).Children under the age of five and some animals, such as dogs, can hear up to \(25\) \(kHz\).
Whales and elephants produce sound in the
infrasound range.
Ultrasound is produced by animals like dolphins, bats and dogs.
Applications of Ultrasound:
Ultrasounds are waves of high frequency (\(Greater\) \(than\) \(20,000\) \(Hertz\)). Ultrasounds can able to travel along well-defined paths even in the presence of obstacles. Ultrasounds are used extensively in industries and for medical purposes.
  • It is extensively used in medical applications like 'sonogram' and SONAR system to detect the sea's depth and enemy submarines. It is also employed in dishwashers.  Another important application of ultrasound is the Galton's whistle. This whistle is inaudible to the human ear, but the dogs can hear it.
  • Generally, Ultrasound is used to clean parts located in hard to reach places, for example, spiral tube odd shaped parts, electronic components etc. Objects to be cleaned are placed in a cleaning solution, and ultrasonic waves are passed into the solution. Due to the high frequency, the dust, grease, and dirt particles get detached and sent out. The objects thus get thoroughly cleaned.
  • Ultrasounds can be used to identify cracks and flaws in metal blocks. The cracks or flaws inside the metal blocks, which are invisible to our eyes and that reduces the strength of the structure. Ultrasonic waves are made to pass through the metal block, and detectors are placed at the other to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected, indicating the presence of the flaw or defect.
  • Ultrasonic waves are used to capture the images of the heart and problems associated with the heart. This method is called Echocardiography.
  • Ultrasonography is commonly used to obtain images of internal body organs such as kidney, liver, uterus. It helps the doctor to diagnose and treat problems in the body of the patient. In this method, ultrasound waves are made to travel through the body to the organ under consideration, waves that get reflected are converted to electrical signals that can be monitored on a screen.
  • Ultrasound waves may be employed to break small stones formed in the kidneys into small fragments or grains. These grains get flushed out with urine.