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Physics · Waves

Transverse and longitudinal waves

Describe the difference between transverse and longitudinal waves and describe evidence that it is the wave, and not the medium, that travels.

  • 6 key terms
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Student handouts

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Warm-up

Answer each one, then check.

  1. 1

    What do waves transfer?

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    Energy

  2. 2

    Give an example of a wave.

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    Sound, light or water ripples

  3. 3

    What is a medium?

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    The material a wave travels through

  4. 4

    What is a vibration?

    Show answerHide answer

    A repeated back-and-forth movement

  5. 5

    What do sound waves travel through?

    Show answerHide answer

    Solids, liquids and gases

Learning Objectives

  1. 1Describe the difference between transverse and longitudinal waves.
  2. 2Give examples of each.
  3. 3Describe compressions and rarefactions.
  4. 4Describe evidence that in ripples and sound it is the wave, not the water or air, that travels.

TWO TYPES OF WAVE

In a transverse wave the vibrations are at right angles to the direction the wave travels. In a longitudinal wave the vibrations are parallel to the direction of travel.

Waves transfer energy (and information) from one place to another without transferring matter.

Transverse or Longitudinal?

Transverse

  • Vibrations are at right angles to the direction of travel.
  • Examples: ripples on water, electromagnetic waves, waves on a rope.
  • Have crests and troughs.

Longitudinal

  • Vibrations are parallel to the direction of travel.
  • Examples: sound waves, P-waves.
  • Have compressions and rarefactions.

Evidence That the Wave Travels

Describe evidence that in water ripples it is the wave, and not the water, that moves.

Show the solutionHide the solution
  1. 1 Float a cork on a pond As ripples pass, the cork bobs up and down
  2. 2 Observe The cork does not travel along with the wave
  3. 3 Conclusion The water vibrates but does not move with the wave

AnswerThe cork moves up and down in the same place, so the water itself does not travel.

Sound in Air

Explain why sound waves are longitudinal.

Show the solutionHide the solution
  1. 1 Air particles Vibrate backwards and forwards in the direction the wave travels
  2. 2 Compressions Regions where the particles are pushed close together
  3. 3 Rarefactions Regions where the particles are spread out

AnswerSound is a longitudinal wave with compressions and rarefactions.

Key Points

Learn these.

  • Energy, not matter

    Waves transfer energy without transferring matter.

  • Medium

    Mechanical waves need a medium; electromagnetic waves do not.

  • Sound evidence

    Particles in air vibrate about fixed positions; smoke in a tube just vibrates back and forth.

  • Don't say

    'The water moves along'. The water just moves up and down.

Wave Types

Classify each wave as transverse or longitudinal: (a) light (b) sound in air (c) ripples on a pond (d) a wave on a rope shaken up and down.

1. Is vibration at right angles?

2. Or parallel?

A good answer shows: (a) Transverse (b) Longitudinal (c) Transverse (d) Transverse.

Can I...?

  1. 1Define transverse.
  2. 2Define longitudinal.
  3. 3Give examples.
  4. 4Name compressions and rarefactions.
  5. 5Describe the cork evidence.
  6. 6Say waves transfer energy.
  7. 7Explain sound in air.
  8. 8Draw both wave types.

Summary & Exam Focus

  • Transverse: vibrations at right angles; longitudinal: parallel.
  • Sound is longitudinal; ripples are transverse.
  • Compressions and rarefactions in longitudinal waves.
  • The wave, not the medium, travels.

Exam focus

Describe the difference between a transverse wave and a longitudinal wave. (2 marks) (2 marks)

Direction of vibration relative to the direction of travel.

Key terms

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

Transverse wave
A wave with vibrations at right angles to the direction of travel.
Longitudinal wave
A wave with vibrations parallel to the direction of travel.
Compression
A region where particles are close together.
Rarefaction
A region where particles are spread out.
Medium
The material a wave travels through.
Oscillation
A back-and-forth movement.

Questions and answers

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

1. Exam question Describe 2 marks Easier

Describe the difference between a transverse wave and a longitudinal wave.

Mark scheme — 2 marks available

  • Transverse: at right angles — 1 mark
  • Longitudinal: parallel — 1 mark

Model answer

In a transverse wave the vibrations are at right angles to the direction of travel of the wave. In a longitudinal wave the vibrations are parallel to the direction of travel.

2. Exam question State 2 marks Easier

Give one example of a transverse wave and one example of a longitudinal wave.

Mark scheme — 2 marks available

  • A transverse wave — 1 mark
  • A longitudinal wave — 1 mark

Model answer

Transverse: ripples on water, light or other electromagnetic waves. Longitudinal: sound waves in air.

3. Exam question Describe 3 marks Easier

Describe how a longitudinal wave, such as a sound wave, travels through air. Use the words compression and rarefaction.

Mark scheme — 3 marks available

  • Particles vibrate parallel to travel — 1 mark
  • Compressions: particles close together — 1 mark
  • Rarefactions: particles spread out — 1 mark

Model answer

The air particles vibrate back and forth parallel to the direction the wave travels. The wave consists of regions where the particles are pushed together (compressions) and regions where they are spread out (rarefactions), which move through the air.

4. Exam question Describe 3 marks Easier

A cork floats on water. Ripples pass it. Describe what happens to the cork and explain what this shows about the wave.

Mark scheme — 3 marks available

  • Cork moves up and down — 1 mark
  • Cork does not move along with the wave — 1 mark
  • The wave, not the water, travels (energy transferred) — 1 mark

Model answer

The cork moves up and down but does not travel along with the wave. This shows that the wave transfers energy but the water itself does not move along.

5. Exam question Explain 3 marks Easier

Explain why sound cannot travel through a vacuum but light can.

Mark scheme — 3 marks available

  • Sound needs a medium or particles — 1 mark
  • No particles in a vacuum — 1 mark
  • Light does not need a medium — 1 mark

Model answer

Sound is a longitudinal wave that needs particles to vibrate, so it needs a medium. Light is an electromagnetic wave and does not need a medium.

6. Multiple choice 1 mark Easier

Sound waves are...

  1. A transverse
  2. B longitudinal Correct
  3. C electromagnetic
  4. D static

Why: Compressions and rarefactions.

7. Multiple choice 1 mark Core

In a transverse wave vibrations are...

  1. A parallel to the direction
  2. B zero
  3. C at right angles to the direction of travel Correct
  4. D random

Why: That defines it.

8. Multiple choice 1 mark Core

A compression is a region where particles are...

  1. A far apart
  2. B stationary
  3. C hot
  4. D close together Correct

Why: Higher pressure.

9. Multiple choice 1 mark Core

Waves transfer...

  1. A energy Correct
  2. B matter only
  3. C mass
  4. D charge only

Why: Not matter.

10. Multiple choice 1 mark Stretch

A cork on water bobs up and down. This shows the...

  1. A cork is magnetic
  2. B water does not travel with the wave Correct
  3. C wave is longitudinal
  4. D water is solid

Why: Only the wave travels.