हिंदी
Tamil Nadu Board of Secondary EducationSSLC (English Medium) Class 9

Properties of Sounds - Loudness and Intensity

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Intensity of Sound and Sound Level:

The intensity and sound level tell us how loud or soft a sound is. Sound level refers to the intensity of sound as perceived by our ears.

  • The intensity of sound depends on the square of the amplitude of the vibration.
  • If the amplitude is doubled, the intensity becomes 4 times greater (since 22 = 4). This shows that even small changes in amplitude can cause large changes in intensity.
  • The decibel (dB) is the unit used to measure sound level.
  • It is named after Alexander Graham Bell, the inventor of the telephone, in recognition of his work on sound.
  • When the intensity of sound increases by 10 times, the sound level rises by 10 dB.

This means a small increase in sound intensity can make a noticeable increase in the sound level we hear.

Decibel levels of some common sounds:

  • Beginning of audible sound: 0 dB
  • Normal breathing: 10 dB
  • Murmuring from 5 metres away: 30 dB
  • Normal conversation (between two persons): 60 dB
  • Heavy traffic: 70 dB
  • Ordinary factories – 80 dB
  • Jet engine: 130 dB
  • Start of ear-splitting sound: 120 dB

Hearing is temporarily affected by sounds of frequency greater than 1000 Hz and levels higher than 100 dB. This can result in temporary deafness. Workers who work near aeroplane engines experience this.

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