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Physics · Waves

Sound waves and hearing

Describe how sound waves cause vibrations in solids and in the ear, and explain why human hearing is limited to a range of frequencies (Physics only, Higher tier).

  • Higher
  • 6 key terms
  • All boards
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Warm-up

Answer each one, then check.

  1. 1

    What type of wave is sound?

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    Longitudinal

  2. 2

    What is frequency?

    Show answerHide answer

    Waves per second

  3. 3

    What does a vibration do?

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    Moves back and forth

  4. 4

    Name part of the ear.

    Show answerHide answer

    Ear drum

  5. 5

    What is ultrasound?

    Show answerHide answer

    Sound above 20 kHz

Learning Objectives

  1. 1Describe how sound waves can be converted to vibrations in solids, and vice versa.
  2. 2Describe how the ear drum and other parts of the ear convert sound into the sensation of sound.
  3. 3Explain why the conversion only works over a limited frequency range.
  4. 4State the range of normal human hearing: 20 Hz to 20 kHz.

SOUND AND HEARING

Sound waves can travel through solids causing vibrations in the solid. In the ear, sound waves make the ear drum and other parts vibrate, giving the sensation of sound.

The range of normal human hearing is from 20 Hz to 20 kHz.

Sound to Vibration

Describe how sound waves cause the sensation of hearing.

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  1. 1 Sound wave Compressions and rarefactions reach the ear drum
  2. 2 Ear drum Vibrates at the same frequency as the wave
  3. 3 Small bones Pass the vibrations to the cochlea
  4. 4 Cochlea Converts the vibrations to electrical signals sent to the brain

AnswerSound waves make the ear drum vibrate; the vibrations are passed on and converted to nerve impulses.

Limited Range

Explain why humans cannot hear sounds above 20 kHz.

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  1. 1 Structure The ear drum and bones can only vibrate at limited frequencies
  2. 2 High frequency Too fast for them to follow
  3. 3 Result No sensation of sound

AnswerThe parts of the ear cannot vibrate fast enough; the range of hearing is limited.

Other Conversions

Give an example of sound waves being converted to vibrations in a solid.

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  1. 1 Sound hits a surface A wall or window vibrates slightly
  2. 2 Microphone The diaphragm vibrates
  3. 3 Loudspeaker A cone vibrates to make sound waves

AnswerA sound wave makes a solid vibrate; a vibrating solid makes sound waves.

Key Facts

Learn these numbers.

  • Hearing range

    About 20 Hz to 20 kHz for humans (20 000 Hz).

  • Infrasound

    Below 20 Hz.

  • Ultrasound

    Above 20 kHz.

  • Age

    The upper limit falls with age.

Hearing Range

Convert 20 kHz to Hz. A dog whistle produces a sound of 25 kHz. Can a human hear it? Explain.

1. Compare with 20 Hz to 20 kHz.

A good answer shows: 20 kHz = 20 000 Hz. 25 kHz is above the upper limit, so a human cannot hear it (but a dog can).

Can I...?

  1. 1Describe the ear drum.
  2. 2Describe the route in the ear.
  3. 3State the hearing range.
  4. 4Explain the limited range.
  5. 5Give examples of conversion.
  6. 6Define ultrasound.
  7. 7Define infrasound.
  8. 8Convert kHz to Hz.

Summary & Exam Focus

  • Hearing range 20 Hz to 20 kHz.
  • Ear drum vibrates, then bones, then cochlea.
  • Only works over a limited frequency range.
  • Ultrasound is above 20 kHz.

Exam focus

State the range of normal human hearing. (1 mark) (1 marks)

20 Hz to 20 kHz.

Key terms

The vocabulary this lesson expects you to use. Each one is linked from the first place it appears above.

Ear drum
A thin membrane in the ear that vibrates with sound.
Cochlea
A coiled part of the inner ear that turns vibrations into signals.
Frequency range
The span of frequencies a device or ear can respond to.
Infrasound
Sound below 20 Hz.
Ultrasound
Sound above 20 kHz.
Vibration
A repeated back-and-forth movement.

Practice questions

Have a go at each one before you open its answer.

  1. Question 1 State 1 mark

    State the range of frequencies of normal human hearing.

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    Model answer

    20 Hz to 20 kHz (20 000 Hz).

    Mark scheme

    • 20 Hz to 20 kHz — 1 mark
  2. Question 2 Describe 3 marks

    Describe how sound waves in air are converted into the sensation of sound in the ear.

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    Model answer

    The sound waves make the ear drum vibrate. The vibrations are passed through small bones to the cochlea, which converts them to electrical signals sent by the nerve to the brain.

    Mark scheme

    • Ear drum vibrates — 1 mark
    • Vibrations passed on through the bones — 1 mark
    • Converted to signals to the brain — 1 mark
  3. Question 3 Explain 3 marks

    Explain why humans cannot hear sounds with a frequency of 30 kHz.

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    Model answer

    The ear drum and the other parts of the ear can only vibrate over a limited range of frequencies. A frequency of 30 kHz is above the upper limit of 20 kHz, so they do not respond.

    Mark scheme

    • Ear parts vibrate only over a limited range — 1 mark
    • 30 kHz is above 20 kHz — 1 mark
    • So no sensation of sound — 1 mark
  4. Question 4 Describe 2 marks

    A loudspeaker converts electrical signals to sound waves. Describe what happens to the cone.

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    Model answer

    The cone vibrates, making the air vibrate and creating sound waves.

    Mark scheme

    • Cone vibrates — 1 mark
    • Produces sound waves in the air — 1 mark
  5. Question 5 Calculate 2 marks

    A dog can hear a sound of 40 kHz. Convert 40 kHz to hertz and state whether a human could hear it.

    Show answerHide answer

    Model answer

    40 000 Hz; no, it is above 20 kHz.

    Mark scheme

    • 40 000 Hz — 1 mark
    • No, above the human limit — 1 mark

Quick check

  1. The lowest frequency humans hear is about...

    1. A2 Hz
    2. B20 Hz
    3. C200 Hz
    4. D2000 Hz
    Show answerHide answer

    B: 20 Hz

    20 Hz.

  2. The highest frequency humans hear is about...

    1. A2 kHz
    2. B200 kHz
    3. C20 kHz
    4. D2000 kHz
    Show answerHide answer

    C: 20 kHz

    20 000 Hz.

  3. Sound makes the ear drum...

    1. Amelt
    2. Bglow
    3. Crotate
    4. Dvibrate
    Show answerHide answer

    D: vibrate

    It moves with the wave.

  4. Sound above 20 kHz is called...

    1. Aultrasound
    2. Binfrasound
    3. Clight
    4. Dstatic
    Show answerHide answer

    A: ultrasound

    Above human hearing.

  5. Hearing is limited because the ear parts...

    1. Aare too large
    2. Bcan only vibrate over a limited range
    3. Care not connected
    4. Dare made of glass
    Show answerHide answer

    B: can only vibrate over a limited range

    They cannot follow very fast vibrations.

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