Sound Waves (Cambridge (CIE) IGCSE Physics)

Describing sound

• Sound waves are produced by vibrating sources

• Sound waves are Longitudinal

  • So a medium is needed to transmit sound waves

  • This means if there are no molecules, such as in a vacuum, then the sound can’t travel through it

• When a sound wave comes into contact with a solid, the longitudinal wave vibrations are 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

Representing longitudinal waves

• Longitudinal waves are usually drawn as several lines to show that the wave is moving parallel to the direction of energy transfer

  • Drawing the lines closer together represents the compressions

  • Drawing the lines further apart represents the rarefactions

Representing a longitudinal wave with compression and rarefaction

Longitudinal waves are represented as sets of lines with rarefactions and compressions

Compression & rarefaction

Extended tier only

• Longitudinal waves consist of compressions and rarefactions:

  • A compression is a region of higher density i.e. a place where the molecules are bunched together

  • A rarefaction is a region of lower density i.e. a place where the molecules are spread out

Compression and rarefaction

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

Compression and rarefaction in contact with a solid

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