MCQ Detailed View

Sound is a type of mechanical wave that travels through a medium such as air, water, or solids. The human ear can only hear sound within a specific frequency range, which is about 20 Hz to 20,000 Hz (20 kHz). This is known as the audible range. Any sound outside this range cannot be heard by humans.

When the frequency of sound is below 20 Hz, it is called infrasonic sound. These very low-frequency waves are too slow for the human ear to detect, but many animals can sense them. For example, elephants and whales communicate using infrasonic sounds that can travel long distances.

Infrasonic waves have interesting applications and effects. They are used in geophysics to monitor volcanic eruptions, earthquakes, and even severe weather events, since natural phenomena often produce low-frequency vibrations. Scientists study infrasonic signals to predict earthquakes and monitor atmospheric changes.

On the other side of the spectrum, sounds above 20,000 Hz are called ultrasonic waves. These are widely used in medical imaging (like ultrasound), cleaning instruments, and sonar technology. Supersonic, in contrast, is not a type of sound wave but refers to objects moving faster than the speed of sound.

The main difference between audible, infrasonic, and ultrasonic sounds lies in the frequency:

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  Infrasonic: below 20 Hz (inaudible to humans)

  
  


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  Audible sound: 20 Hz to 20,000 Hz (human hearing range)

  
  


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  Ultrasonic: above 20,000 Hz (inaudible to humans but useful in technology)

  
  

In summary, when sound has a frequency below 20 Hz, it is known as infrasonic sound. It cannot be heard by us, but it plays an important role in science, nature, and technology.