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13.5Chapter 13: Sound Waves

Chapter 13 Review: Sound Waves — Alhussan Physics - Stage 9 Revision Notes & Topical Questions

5 min read 7 parts Lesson 5 of 5 1 quiz

📚 Alhussan Physics - Stage 9 Hub / Topical Revision
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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

Amplitude
  • The height from the centre line to a peak.
Wavelength
  • The distance between two peaks.
Frequency
  • The number of complete waves each second, found by counting waves and dividing by the time.
Pitch and frequency
  • A 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

Loudness
  • Tall waves mean a loud sound and small waves mean a soft sound.
Pitch
  • Closely packed waves mean a high pitch and widely spaced waves mean a low pitch.
Comparing traces
  • Look at both height and spacing, with the same time scale on the screen.

Part 3 of 5Properties of sound

Longitudinal
  • Sound is a longitudinal wave that needs a medium, so it cannot travel through a vacuum.
Speed
  • Speed = frequency × wavelength, and in air it is typically about 330 m/s.
In different materials
  • Sound 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

Constructive
  • Waves in step add up, so the sound is louder.
Destructive
  • Waves out of step cancel out, so the sound is quieter.
Uses
  • Interference is used to tune instruments and in noise-cancelling headphones.
Microwave oven
  • The turntable rotates food through hot spots, where waves add up, and cold spots, where they cancel, so it heats evenly.

Key terms

TermMeaning
AmplitudeThe maximum displacement of a wave from its rest position.
FrequencyThe number of waves per second, in hertz.
UltrasoundSound above 20 000 Hz.
InterferenceThe adding or cancelling of waves that meet.
Longitudinal waveA wave in which vibrations are parallel to the direction of travel.

Avoid these mistakes

1
Confusing amplitude with frequency — amplitude is loudness and frequency is pitch.
2
Thinking sound travels through a vacuum — it needs a medium.
3
Thinking ultrasound is audible to humans — it is above 20 000 Hz.
4
Thinking sound is fastest in gases — it is fastest in solids.

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