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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 Quantity Unit name Unit symbol Velocity (v) metre per second $$\text{m·s^{-1}}$$ Wavelength (λ) metre m Amplitude (A) metre m Period (T) second s Frequency (f) hertz Hz ($$\text{s^{-1}}$$)

Table 10.6: Units used in sound