• Range of Hearing

    The human ear can hear the sound between frequencies of 20 Hz to 20,000 Hz. Thus, audible range or range of hearing is between 20 Hz to 20,000 Hz; for human beings. However, children under 5 years of age can hear the sound upto 25000 Hz.

     

    Infrasonic Sound or Infrasound

    Sound, below the frequency of 20Hz is called infrasonic or infrasound. Infrasound is produced because of very slow vibration. For example; simple pendulum produces sound below 20Hz. Human being cannot hear infrasound as their ears are not adapted to hear the sound of such range.

    Many animals; such as whale, elephant, rhinoceros, etc. can produce and hear sound having frequencies below 20 Hz. This sound range is also produced during earthquakes & volcanic eruption.

     

    Ultrasound or Ultrasonic Sound

    Sound, above the frequency of 20000 Hz is called ultrasound. Humans cannot hear the ultrasonic sound. However, many animals such as dogs, cat, bat, monkey, deer, etc. can hear ultrasound.

    Bats catch their prey by producing ultrasound. Bat produces ultrasound and detects the reflected sound waves coming from any obstacle; such as a prey. By detecting the reflection of ultrasound, bat understands the position and type of prey or of any obstacle in the way. Some aquatic animals, such as dolphin, also use ultrasound to catch their prey.

     

    Organism

    Hearing Range (Hz)

    Human Being

    20 - 20,000

    Elephant

    16 - 12,000

    Cow

    23 - 35,000

    Rat

    200 - 76,000

    Bat

    2,000 - 110,000

    Horse

    55 - 33,500

    Dog

    67 - 45,000

    Rabbit

    360 - 42,000

     

    Applications of Ultrasound

    (i) It is used to detect cracks in metal blocks in industries without damaging them.

    (ii) It is used in industries to clean ‘hard-to-reach’ parts of objects such as spiral tubes, odd shaped machines etc.

    (iii) Ultrasound waves are used to reflect the action of heart and its images are formed. This technique is called electrocardiogram.

    (iv) Ultrasound waves are used to obtain pictures of internal organs of the body (such as liver, gall bladder, kidneys, uterus & tumour) by using echoes of ultrasound waves. This technique is called ultrasonography.

    (v) Ultrasound is used to split tiny stones in kidneys into fne grains.