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Waves

Sound waves, ultrasound and infrasound

  • 3 things to know
  • Paper 1

Overview

How sound makes solids vibrate and vibrating solids make sound, the 20 Hz to 20 000 Hz range of human hearing, the eardrum, ear bones and cochlea, and ultrasound and infrasound with their frequencies, sources and wavelengths.

What you need to know

Answer each one before you reveal it.

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Key term

Describe what happens when a sound wave in air reaches a solid surface such as a drum skin.

Key term

Describe how a vibrating solid surface produces a sound wave in air.

Key term

Describe the part played by the eardrum in hearing.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Describe what happens when a sound wave in air reaches a solid surface such as a drum skin.

    Model answer

    The changing air pressure pushes the surface back and forth, making it vibrate at the same frequency as the sound.

  2. 2

    Describe how a vibrating solid surface produces a sound wave in air.

    Model answer

    The moving surface pushes on the air next to it, creating compressions and rarefactions that travel away as sound.

  3. 3

    Explain why a solid can only convert sound over a limited range of frequencies.

    Model answer

    The solid has mass and stiffness, so it cannot follow vibrations that are too rapid nor respond well to those that are too slow.

  4. 4

    State the approximate range of frequencies a healthy human ear can detect.

    Model answer

    From about 20 Hz to about 20 000 Hz.

  5. 5

    Describe the part played by the eardrum in hearing.

    Model answer

    The arriving sound wave makes the eardrum vibrate at the same frequency as the sound.

  6. 6

    Describe how the vibration is passed from the eardrum to the inner ear.

    Model answer

    Three small bones carry the vibration from the eardrum to the oval window, increasing the force applied.

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