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Transverse and longitudinal waves Edexcel International A Level Physics revision

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In plain words

Shake a rope up and down and the wave runs along it while the rope itself moves across: that is transverse. Push a slinky back and forth and the coils bunch up and spread out along the line the wave is travelling: that is longitudinal. Light is the first kind and sound is the second.

4 things to know

  1. Transverse wave: the oscillations are at right angles to the direction the wave travels. Examples: all electromagnetic waves, waves on a string, ripples on water.
  2. Longitudinal wave: the oscillations are along the direction of travel. Sound is the main example. It travels as compressions (higher pressure, particles closer together) and rarefactions (lower pressure, particles further apart).
  3. Both kinds can be drawn as a displacement–distance or displacement–time graph. For a longitudinal wave the graph still plots how far each particle is from its rest position; it is not a picture of the wave.
  4. At the centre of a compression or a rarefaction the particles are at their rest positions, and that is where the pressure is furthest from normal.

Tips and tricks

  • A displacement graph of a sound wave looks like a transverse wave. It isn't one: read the axes.
  • The wavelength of a longitudinal wave is the distance between the centres of two neighbouring compressions.
5 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Transverse and longitudinal waves: 5 questions and answers

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

  1. Which is a longitudinal wave?
    • light
    • a wave on a string
    • sound (the answer)
    • a radio wave

    The particles oscillate along the direction of travel.

  2. In a transverse wave, how do the oscillations lie compared with the direction of travel?
    • at right angles to it (the answer)
    • along it
    • at 45° to it
    • in circles round it

    That is the definition of transverse.

  3. What is a rarefaction?
    • a region of lower pressure, where the particles are further apart (the answer)
    • a region of higher pressure, where the particles are closer together
    • a point that never moves
    • the peak of a transverse wave

    It is the opposite of a compression.

  4. The centre of a compression is 0.25 m from the centre of the next rarefaction. What is the wavelength?
    • 0.125 m
    • 0.25 m
    • 0.50 m (the answer)
    • 1.0 m

    Compression to rarefaction is half a wavelength.

  5. Which of these is a transverse wave?
    • sound in air
    • light (the answer)
    • ultrasound
    • a push-pull pulse along a spring

    All electromagnetic waves are transverse.

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