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13.3Chapter 13: Sound Waves

Hearing, decibels, and risk — Alhussan Physics - Stage 9 Revision Notes & Topical Questions

5 min read 8 parts Lesson 3 of 5 1 quiz

📚 Alhussan Physics - Stage 9 Hub / Topical Revision
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Lesson summary

Physics 13.3 Hearing, decibels, and risk — Decibel Scale and Noise-Induced Hearing Loss — Alhussan International Academy — Physics (Stages 7–9) notes: Name the unit of sound intensity and describe the risks of loud sounds and how to reduce them.Intensity — The loudness of a sound…

  • Not like a ruler
  • Loudest possible
  • Sudden loud sounds
  • Long exposure
  • Reducing risk
  • Decibel meters

Section 1 of 8The decibel scale

Intensity
  • The loudness of a sound is measured with a sound-level meter on the decibel (dB) scale.
Noise
Noise sounds that we do not want to hear.
Not like a ruler
  • Every increase of 10 dB increases the intensity 10 times.
  • A 40 dB sound has 10 times the intensity of a 30 dB sound.
  • A 50 dB sound has 100 times the intensity of a 30 dB sound.
Loudest possible
  • The loudest possible continuous sound is 194 dB; explosions and earthquakes can be louder but do not last.

Section 2 of 8Typical sound levels

SoundApproximate level
Threshold of hearing0 dB
Quiet whisper30 dB
Normal conversation60 dB
Busy road80 dB
Chainsaw, can damage hearing after about 8 hours a day90 dB
Rock concert, loud headphones100 to 110 dB
Vuvuzela, painful120 dB
Jet engine nearby140 dB

Section 3 of 8Hearing damage

Sudden loud sounds
  • They can burst the eardrum.
Long exposure
  • It damages the tiny hair cells in the inner ear, which do not grow back, causing permanent noise-induced hearing loss.
Time
  • The risk depends on both the loudness in decibels and the length of time of exposure.

Section 4 of 8Understanding risk

Risk
  • It combines the probability that something bad happens with the consequence if it did.
Examples
  • An aeroplane crash has serious consequences but a very low probability.
  • Listening to loud music may not seem risky, but the probability of hearing damage rises the longer you listen.
Reducing risk
  • A risk can be reduced by lowering the probability or the consequences.

Section 5 of 8Reducing the risk from noise

Shielding
  • Put something between the sound source and your ears, such as ear defenders.
Distance
  • Move away from the source of the sound.
Time
  • Reduce the time spent near the source.
Decibel meters
  • People can use them to monitor sound levels.
Headphones
  • Lower the volume, take breaks and use noise-cancelling headphones so the volume does not need to be raised.

Section 6 of 8Protecting hearing at work

Ear defenders
  • They reduce the intensity of sound reaching the ear.
  • Construction workers using drills, airport ground crew, factory workers and musicians should wear them.
Other risks
  • Tiredness from long periods of driving also raises the probability of accidents.

Section 7 of 8Key terms

TermMeaning
Decibel (dB)The unit of sound intensity or loudness.
IntensityThe amount of sound energy arriving per unit area.
NoiseSound that we do not want to hear.
RiskThe probability of harm combined with how serious the harm would be.
Ear defendersProtective covers that reduce the sound reaching the ears.

Section 8 of 8Exam technique

1
Thinking decibels are like a ruler — each 10 dB is a tenfold change in intensity.
2
Thinking only very loud sounds are dangerous — long exposure to moderately loud sounds also damages hearing.
3
Thinking hair cells in the ear regrow — the damage is permanent.
4
Thinking risk depends only on consequence — probability matters too.

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