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Sound Summary Class 8 NCERT Summary Chapter 11

Introduction

Sound Summary Class 8 NCERT Summary Chapter 11

  • Sound helps us to communicate with one another and plays an important role in our life.
  • Vibrating body produces sound.
  • In this chapter, we will know about how sound is produced and how we hear them.

Vibration motion

Sound Summary Class 8 NCERT Summary Chapter 11

  • to-and-fro or back-and-forth or up-and-down motion of a body.
  • Sound is a form of energy that is produced by producing vibration in an object.
  • Sound cannot move through vacuum.
  • Sound waves are longitudinal waves.

How sound is produced by Humans?

Sound Summary Class 8 NCERT Summary Chapter 11


  • In humans, sound is produced by voice box or larynx.
  • When the lungs force air through the slit, the vocal cord vibrates which produce sound.
  • Sometimes, the amplitude of produced sound is so small that we can't hear them.
  • The muscles attached to the vocal cords can make the cords tight or loose to produce different types of sounds.
  • Different people have different vocal chords. Due to this reason, we all have a different voice quality.

Propagation of Sound

Sound Summary Class 8 NCERT Summary Chapter 11

  • Sound requires material medium for propagation.
  • Sound can travel through solid, liquid or gas.
  • Sound cannot travel through vacuum.
  • No sound can be heard in outer spaces.

Frequency

  • Frequency is measure of number of oscillations per second.
  • It is measured in hertz(Hz).

Loudness of sound

Sound Summary Class 8 NCERT Summary Chapter 11

  • It is measured in decibel (dB).
  • It depends on amplitude.
  • Higher amplitude– louder sound
    • Pitch or shrillness depends on frequency.
  • Higher frequency– higher pitch
  • Audible sound– Human ear can hear sounds having frequency in the range of 20-20,000 Hz.

Noise

  • Unpleasant sound is called noise.

Noise pollution

  • Presence of unwanted and excessive sound in the environment
  • Noise pollution may cause many health related problems.

Measures to control noise pollution

  • Moving noise producing industries away from residential area.
  • Minimizing the usage of loud speakers.
  • Avoiding unnecessary usage of horns
  • Planting more and more trees.

Human Ear

Sound Summary Class 8 NCERT Summary Chapter 11

  • Human ear has three parts outer, middle and inner.
  • Shape of the outer part of the ear is like a funnel.
  • In human ear, the eardrum vibrates and passes vibration to the inner ear.
  • The eardrum is like a stretched rubber sheet.
  • Sound vibrations make the eardrum vibrate, from there the signal goes to the brain.
  • Noise level of 85 dB can damage the human ear.
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