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Properties of waves Cambridge IGCSE Co-ordinated Sciences (9–1) revision

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In plain words

A wave carries energy from place to place without carrying the stuff it travels through. A Mexican wave goes round a stadium, but everybody stays in their seat. Wave speed is how many waves pass each second, times how long each one is.

Three things to know

  1. Waves transfer energy without transferring matter. In a transverse wave the vibrations are at right angles to the direction of travel (light, water waves); in a longitudinal wave they are along it (sound).
  2. Wave speed = frequency × wavelength (v = fλ). Frequency is the number of waves each second, in hertz.
  3. Waves can be reflected, refracted (change speed and direction) and diffracted (spread out through a gap).

Worked example

A wave has a frequency of 50 Hz and a wavelength of 0.2 m. Find its speed.

  1. v = f × λ.
  2. = 50 × 0.2 = 10 m/s.

Tips and tricks

  • Transverse: the vibrations are at right angles to the direction of travel (light, water). Longitudinal: they are along it (sound).
  • When a wave changes speed, its frequency stays the same. Only the speed and the wavelength change.
6 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Properties of waves: 6 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

  1. What do waves transfer?
    • matter
    • energy (the answer)
    • mass
    • particles

    The medium vibrates but does not travel with the wave.

  2. Which is a longitudinal wave?
    • light
    • a water ripple
    • sound (the answer)
    • a radio wave

    In sound the air vibrates back and forth along the direction of travel.

  3. A wave has frequency 10 Hz and wavelength 3 m. What is its speed?
    • 0.3 m/s
    • 3.3 m/s
    • 13 m/s
    • 30 m/s (the answer)

    v = fλ = 10 × 3.

  4. What is the amplitude of a wave?
    • the distance between two crests
    • the maximum displacement from the rest position (the answer)
    • the number of waves per second
    • the time for one wave

    It is the height of a crest above the middle line.

  5. What happens to a wave's frequency when it passes from deep to shallow water?
    • It increases.
    • It decreases.
    • It stays the same. (the answer)
    • It becomes zero.

    The speed and wavelength change, but the same number of waves arrive each second.

  6. Waves spread out after passing through a narrow gap. What is this called?
    • reflection
    • refraction
    • diffraction (the answer)
    • dispersion

    Diffraction is the spreading of waves at a gap or edge.

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