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PHYSICS · Stage 9 · Chapter 13: Sound Waves

Physics 13.5 Chapter 13 Review: Sound Waves

5 min read 5 parts Lesson 5 of 5

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Lesson summary

Physics 13.5 Chapter 13 Review: Sound Waves — Alhussan International Academy — Physics (Stages 7–9) notes: Summarise Chapter 13 on amplitude, frequency, pitch, ultrasound, hearing and interference.Amplitude — The height from the centre line to a peak.Wavelength — The distance bet…

  • Pitch and frequency
  • Comparing traces
  • Longitudinal
  • In different materials
  • Audible range
  • Constructive

Part 1 of 5Reading a wave

  • AmplitudeThe height from the centre line to a peak.
  • WavelengthThe distance between two peaks.
  • FrequencyThe number of complete waves each second, found by counting waves and dividing by the time.
  • Pitch and frequencyA note of 1500 Hz makes 1500 waves per second, and a wave of half that frequency has 750 waves per second, so it shows half as many waves on the same screen and has a lower pitch.

Part 2 of 5Loud, soft, high and low

  • LoudnessTall waves mean a loud sound and small waves mean a soft sound.
  • PitchClosely packed waves mean a high pitch and widely spaced waves mean a low pitch.
  • Comparing tracesLook at both height and spacing, with the same time scale on the screen.

Part 3 of 5Properties of sound

  • LongitudinalSound is a longitudinal wave that needs a medium, so it cannot travel through a vacuum.
  • SpeedSpeed = frequency × wavelength, and in air it is typically about 330 m/s.
  • In different materialsSound travels faster in solids and liquids than in gases, because particles are closer and pass on vibrations more quickly.

Part 4 of 5Ultrasound and hearing

  • Ultrasound — Sound with a frequency above 20 000 Hz, which humans cannot hear.
    • A whistle of 1500 Hz is audible.
    • Uses include medical scans, sonar and cleaning.
  • Audible range — About 20 Hz to 20 000 Hz for humans, shrinking with age.
  • Risk — Decibels measure intensity and long exposure to loud sounds can damage hearing.

Part 5 of 5Interference

  • ConstructiveWaves in step add up, so the sound is louder.
  • DestructiveWaves out of step cancel out, so the sound is quieter.
  • UsesInterference is used to tune instruments and in noise-cancelling headphones.
  • Microwave ovenThe turntable rotates food through hot spots, where waves add up, and cold spots, where they cancel, so it heats evenly.

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