Sound Waves (AQA GCSE Physics)
Revision Note
Sound Waves in Solids
Higher Tier Only
Sound waves are vibrations of air molecules
When a sound wave comes into contact with a solid those vibrations can be transferred to the solid
For example, sound waves can cause a drinking glass to vibrate
If the glass vibrates too much the movement causes the glass to shatter
Sound is an example of a longitudinal wave, hence it consists of:
Compressions - regions of higher density
Rarefactions - regions of lower density
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
When sound waves hit a solid, the fluctuating pressure causes the solid to vibrate
Sound Waves in the Ear
Higher Tier Only
Sound waves can be heard by human beings because sound waves are transferred from the air to the solid components of the ear
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
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 then transfers the vibrations to the inner ear
In the inner ear, nerve cells detect the sound and send a message to the brain giving the sensation of sound
The human ear is made up of several components which turn sound waves into signals which the brain can interpret
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
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