Production and Propagation of Sound and its Characteristics: NCERT / CBSE Revision Notes


What is Sound?


Sound is a form of energy that causes the sensation of hearing. Sound needs a medium to travel. Sound travels through gases, liquids and solids. The speed of sound is the maximum in solids, less in liquids and the least in gases. Sound cannot travel through vacuum.



In humans, sound is produced by the voice box or the Larynx. Larynx or the voice box is present in the upper portion of the wind pipe of the throat that enables humans to produce sound. The vocal cords in men are about 20 millimetres long, in women about 15 millimetres long; children have very short vocal cords.

The vibrations of a body while producing sound may not always be clearly visible to the human eye.

We hear sound with our ears. The ear drum has a vibrating membrane like a stretched rubber sheet. When a sound note reaches the ear, the ear drum vibrates, and the vibrations get converted into signals that are carried to the brain to get a sensation of hearing. 

Read more: NCERT Notes

 Production Of Sound


When air is forced by the lungs through the slit, the vocal cords vibrate, producing sound.
  • To produce pleasant sounds, a number of musical instruments have been developed
  •  Some instruments produce sound due to the vibration of membranes, The tabla, cymbals, ghatam, kartal and manjira are some instruments that work on the vibration of a membrane.
  •  Some due to the vibration of strings, the sitar, veena, violin, guitar and ektara are some stringed instruments.
  •  Some others produce sound due to the vibration of an air column; Instruments like the flute and the trumpet produce sound due to the vibration of an air column present in them. 

Characteristics of sound

  1. Sound is a form of energy produced by a vibrating body. Sound requires a medium for its propagation. Sound does not propagate in vacuum.
  2. The to and fro or back and forth motion of an object is called vibration. Some instruments produce sound due to the vibration of membranes, some due to the vibration of strings, and some others produce sound due to the vibration of an air column.
  3. The maximum displacement of a vibrating particle from its mean or equilibrium position is called its amplitude.
  4. The time taken by the vibrating particle for one full vibration or oscillation is called the time period of vibration.
  5. The number of vibrations per second is called the frequency. Frequency is measured hertz (Hz).
  6. Sound produced by any means has the following characteristics, namely, loudness, pitch or shrillness, and quality or timbre.
  7. The loudness of sound depends on its amplitude. The loudness of sound is proportional to the square of the amplitude. A roar of a lion is louder than a woman’s voice.
  8. The pitch of sound depends on its frequency. If frequency is more, then the pitch or shrillness is more. The pitch of a woman’s voice is more and it is shriller then a man’s voice.
  9. The loudness of sound is measured in Decibel (db). If loudness exceeds 80 db, then the sound becomes physically painful.
  10. Not all sound produced by vibrating bodies is audible. The human ear can recognise the sounds of frequencies in the range of 20 Hz to 20,000 Hz. This range of frequency of sound is called audible sound.
  11. Some animals like dogs and snakes can hear sounds of frequencies greater than 20,000 Hz. Sounds of frequencies less than 20 Hz are called infrasonic sounds, while sounds of frequencies greater than 20,000 Hz are called ultrasonic sounds

Noise And Music

Any intolerable and irritating sound is called noise. The word noise comes from the Latin word nausea, meaning seasickness. 

Music refers to any sound that is pleasant to the ear. Sound produced by musical instruments is pleasing to the ear. But if the intensity of the sound exceeds a certain limit, then it is intolerable and becomes noise.

Undesirable sounds and disturbances cause noise pollution. Noise pollution may cause high blood pressure, panic attacks and lack of sleep among those exposed to it. To reduce noise pollution: trees should be planted along roads and in residential areas; factories should not be set up in residential areas; vehicles should not blow horns around schools, hospitals and residential area; TVs and music systems should not be played at high volume.

Continuous exposure to loud noise may cause temporary or even permanent hearing impairment. Sign language is used by the hearing disabled to communicate.

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