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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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Teacher resources

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Student handouts

The same files the students see, to print or hand out.

Warm-up

Answer each one, then check.

  1. 1

    What type of wave is sound?

    Show answerHide answer

    Longitudinal

  2. 2

    What is frequency?

    Show answerHide answer

    Waves per second

  3. 3

    What does a vibration do?

    Show answerHide answer

    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.

Show the solutionHide the solution
  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.

Show the solutionHide the solution
  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.

Show the solutionHide the solution
  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.

Questions and answers

10 questions set on this lesson, with the mark schemes and model answers open.

1. Exam question State 1 mark Easier

State the range of frequencies of normal human hearing.

Mark scheme — 1 mark available

  • 20 Hz to 20 kHz — 1 mark

Model answer

20 Hz to 20 kHz (20 000 Hz).

2. Exam question Describe 3 marks Easier

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

Mark scheme — 3 marks available

  • Ear drum vibrates — 1 mark
  • Vibrations passed on through the bones — 1 mark
  • Converted to signals to the brain — 1 mark

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.

3. Exam question Explain 3 marks Easier

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

Mark scheme — 3 marks available

  • 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

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.

4. Exam question Describe 2 marks Easier

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

Mark scheme — 2 marks available

  • Cone vibrates — 1 mark
  • Produces sound waves in the air — 1 mark

Model answer

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

5. Exam question Calculate 2 marks Easier

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

Mark scheme — 2 marks available

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

Model answer

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

6. Multiple choice 1 mark Easier

The lowest frequency humans hear is about...

  1. A 2 Hz
  2. B 20 Hz Correct
  3. C 200 Hz
  4. D 2000 Hz

Why: 20 Hz.

7. Multiple choice 1 mark Core

The highest frequency humans hear is about...

  1. A 2 kHz
  2. B 200 kHz
  3. C 20 kHz Correct
  4. D 2000 kHz

Why: 20 000 Hz.

8. Multiple choice 1 mark Core

Sound makes the ear drum...

  1. A melt
  2. B glow
  3. C rotate
  4. D vibrate Correct

Why: It moves with the wave.

9. Multiple choice 1 mark Core

Sound above 20 kHz is called...

  1. A ultrasound Correct
  2. B infrasound
  3. C light
  4. D static

Why: Above human hearing.

10. Multiple choice 1 mark Stretch

Hearing is limited because the ear parts...

  1. A are too large
  2. B can only vibrate over a limited range Correct
  3. C are not connected
  4. D are made of glass

Why: They cannot follow very fast vibrations.