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Chapter 17 : Sound

Sound arrow_upward

  • Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing
  • Sound plays an important role in our life. It helps us to communicate with one another.

  • Sound is produced by a Vibrating Body arrow_upward

  • The to and fro or back and forth motion of an object is termed as vibration.
  • When a tightly stretched band is plucked, it vibrates and produces sound.
  • When it stops vibrating, it does not produce any sound.
  • We see that a vibrating object produces sound. In some cases, the vibrations are easily visible to us.
  • But in most cases, their amplitude is so small that we cannot see them. However, we can feel them.

  • Sound needs a medium for Propagation arrow_upward

  • Sound needs a medium to travel.
  • When air has been removed completely, it is said that there is vacuum.
  • The sound cannot travel through vacuum.
  • Sound can travel through any solid.
  • For example, sound can travel through wood or metal.

  • Amplitude, Time Period and Frequency of a Vibration arrow_upward

  • The to and fro motion of an object is known as vibration. This motion is also called oscillatory motion.
  • The number of oscillations per second is called the frequency of oscillation.
  • Frequency is expressed in hertz. Its symbol is Hz.
  • A frequency of 1 Hz is one oscillation per second.
  • Amplitude and frequency are two important properties of any sound.
  • The loudness of sound depends on its amplitude.
  • When the amplitude of vibration is large, the sound produced is loud. When the amplitude is small, the sound produced is feeble.
  • The frequency determines the shrillness or pitch of a sound.
  • If the frequency of vibration is higher we say that the sound is shrill and has a higher pitch.
  • If the frequency of vibration is lower, we say that the sound has a lower pitch.
  • For example, a drum vibrates with a low frequency. Therefore, it produces a low-pitched sound.
  • On the other hand, a whistle has a high frequency and therefore, produces a sound of higher pitch

  • Audible and Inaudible Sounds arrow_upward

  • The sounds of frequencies less than about 20 vibrations per second (20 Hz) cannot be detected by the human ear. Such sounds are called inaudible.
  • On the higher side, sounds of frequencies higher than about 20,000 vibrations per second (20 kHz) are also not audible to the human ear.
  • Thus, for human ear, the range of audible frequencies is roughly from 20 to 20,000 Hz.

  • Noise Pollution arrow_upward

  • Presence of unwanted gases and particles in air is called air pollution.
  • Similarly, presence of excessive or unwanted sounds in the environment is called noise pollution.
  • Major causes of noise pollution are sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers etc.
  • Presence of excessive noise in the surroundings may cause many health related problems.
  • Lack of sleep, hypertension (high blood pressure), anxiety and many more health disorders may be caused by noise pollution.
  • A person who is exposed to a loud sound continuously may get temporary or even permanent impairment of hearing.

  • Measures to Limit Noise Pollution arrow_upward

  • The noisy operations must be conducted away from any residential area.
  • Noise producing industries should be set up away from such areas.
  • Use of automobile horns should be minimized.
  • TV and music systems should be run at low volumes.
  • Trees must be planted along the roads and around buildings to cut down on the sounds reaching the residents, thus reducing the harmful effects of noise pollution.

  • Thank You from Kimavi arrow_upward

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