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Chapter Summary

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Chapter summary

Presentation: VPecu

  • Sound waves are longitudinal waves

  • The frequency of a sound is an indication of how high or low the pitch of the sound is.

  • The human ear can hear frequencies from 20 to \(\text{20 000}\) \(\text{Hz}\). Infrasound waves have frequencies lower than \(\text{20}\) \(\text{Hz}\). Ultrasound waves have frequencies higher than \(\text{20 000}\) \(\text{Hz}\).

  • The amplitude of a sound determines its loudness or volume.

  • The tone is a measure of the quality of a sound wave.

  • The speed of sound in air is around \(\text{340}\) \(\text{m·s$^{-1}$}\). It is dependent on the temperature, height above sea level and the phase of the medium through which it is travelling.

  • Sound travels faster when the medium is hot.

  • Sound travels faster in a solid than a liquid and faster in a liquid than in a gas.

  • Sound travels faster at sea level where the air pressure is higher.

  • The intensity of a sound is the energy transmitted over a certain area. Intensity is a measure of frequency.

  • Ultrasound can be used to form pictures of things we cannot see, like unborn babies or tumours.

  • Echolocation is used by animals such as dolphins and bats to “see” their surroundings by using ultrasound.

  • Ships use sonar to determine how deep the ocean is or to locate shoals of fish.

Physical Quantities


Unit name

Unit symbol

Velocity (v)

metre per second


Wavelength (λ)



Amplitude (A)



Period (T)



Frequency (f)


Hz (\(\text{s$^{-1}$}\))

Table 10.6: Units used in sound