Sound Waves (Edexcel GCSE Physics)

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Sound in Solids

Higher Tier Only

  • Sound waves are vibrations of molecules
  • When a sound wave travelling through a gas or a liquid comes into contact with a solid, some of the energy it is transferring is reflected from the surface of the solid, and some is transmitted through or absorbed by the solid 
    • A reflected sound wave is called an echo

  • Sound is an example of a longitudinal wave, hence it consists of:
    • Compressions - regions of higher density
    • Rarefactions - regions of lower density

Compressions and rarefactions, IGCSE & GCSE Physics revision notes

Sound is a longitudinal wave consisting of compressions and rarefactions - these are areas where the pressure of the air varies with the wave

  • These compressions and rarefactions cause changes in pressure, which vary in time with the wave
    • Therefore, sound is a type of pressure wave

  • When the waves hit a solid, the variations in pressure cause the surface of the solid to vibrate in sync with the sound wave

pressure-waves, IGCSE & GCSE Physics revision notes

When sound waves hit a solid, the fluctuating pressure causes the solid to vibrate

Frequency Response

Higher Tier Only

  • Different solids have a tendency to vibrate at different frequencies 
  • This is called the object's natural frequency
  • As a result, sound waves with a frequency that is close to a particular solid's natural frequency will cause larger vibrations than for sound waves with frequencies much larger or smaller than the solid's natural frequency
  • This means some frequencies of sound are transferred much more efficiently to the solid than others

The Human Ear

Higher Tier Only

  • Sound waves can be heard by human beings because sound waves are transferred efficiently from the air to the solid components of the ear
  • The transmission of sound to the human ear only works over a limited range of frequencies
    • This limits the range of sound frequencies a human can hear

  • The range of frequencies a human can hear is 20 Hz to 20 000 Hz

  • In the case of the human ear, the sound waves are transferred by two main solid components:
    • The eardrum which is made of tissue and skin
    • Three small bones

Human Ear, downloadable IGCSE & GCSE Physics revision notes

The human ear is made up of several components which turn sound waves into signals which the brain can interpret

  • The sound wave travels down the auditory canal towards the eardrum
    • The pressure variations created by the sound wave exert a varying force on the eardrum causing it to vibrate
    • The vibration pattern of the sound waves creates the same pattern of vibration in the eardrum

  • The eardrum vibration is transferred to the three small bones
  • The vibration of these small bones amplifies the vibrations and then transfers the vibrations to the liquid in the cochlea located in the inner ear
    • Tiny hairs inside the cochlea detect the vibrations and create electrical impulses which travel along neurones in the auditory nerve to the brain giving the sensation of sound

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.