AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER
Transverse and longitudinal waves
Waves · Lesson 1 of 12
Teacher copy - includes the notes for whoever is teaching from it.
Warm-up
Answer each one, then check.
1. What do waves transfer?
Energy
2. Give an example of a wave.
Sound, light or water ripples
3. What is a medium?
The material a wave travels through
4. What is a vibration?
A repeated back-and-forth movement
5. What do sound waves travel through?
Solids, liquids and gases
Learning Objectives
1. Describe the difference between transverse and longitudinal waves.
2. Give examples of each.
3. Describe compressions and rarefactions.
4. Describe 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 and Longitudinal Waves
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The direction of vibration compared with travel is the key difference. |
A transverse wave with oscillation at right angles to travel, and a longitudinal wave with compressions and rarefactions.
Transverse or Longitudinal?
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TRANSVERSE |
LONGITUDINAL |
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▸ Vibrations are at right angles to the direction of travel. ▸ Examples: ripples on water, electromagnetic waves, waves on a rope. ▸ Have crests and troughs. |
▸ Vibrations are parallel to the direction of travel. ▸ Examples: sound waves, P-waves. ▸ Have compressions and rarefactions. |
Evidence That the Wave Travels
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Describe evidence that in water ripples it is the wave, and not the water, that moves. |
1. Float a cork on a pond
As ripples pass, the cork bobs up and down
2. Observe
The cork does not travel along with the wave
3. Conclusion
The water vibrates but does not move with the wave
Answer: The cork moves up and down in the same place, so the water itself does not travel.
Sound in Air
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Explain why sound waves are longitudinal. |
1. Air particles
Vibrate backwards and forwards in the direction the wave travels
2. Compressions
Regions where the particles are pushed close together
3. Rarefactions
Regions where the particles are spread out
Answer: Sound 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.
Key Terms
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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. |
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Compression A region where particles are close together. |
Rarefaction A region where particles are spread out. |
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Medium The material a wave travels through. |
Oscillation A back-and-forth movement. |
Your Task: Wave Types
8 minutes
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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.
Note: Ask learners to describe the direction of vibration for each.
Can I...?
☐ Define transverse.
☐ Define longitudinal.
☐ Give examples.
☐ Name compressions and rarefactions.
☐ Describe the cork evidence.
☐ Say waves transfer energy.
☐ Explain sound in air.
☐ Draw both wave types.
Summary
✓ 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.
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EXAM FOCUS Describe the difference between a transverse wave and a longitudinal wave. (2 marks) Direction of vibration relative to the direction of travel. |
Exam Practice: Transverse and longitudinal waves
Answer all questions. Use the mark allocation as a guide to how much to write. · 14 minutes
▸ Question 1 · 2 marks · Describe. Describe the difference between a transverse wave and a longitudinal wave.
▸ Question 2 · 2 marks · State. Give one example of a transverse wave and one example of a longitudinal wave.
▸ Question 3 · 3 marks · Describe. Describe how a longitudinal wave, such as a sound wave, travels through air. Use the words compression and rarefaction.
▸ Question 4 · 3 marks · Describe. A cork floats on water. Ripples pass it. Describe what happens to the cork and explain what this shows about the wave.
▸ Question 5 · 3 marks · Explain. Explain why sound cannot travel through a vacuum but light can.
Question 1 · 2 marks · Describe
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“Describe the difference between a transverse wave and a longitudinal wave.” |
HOW TO ANSWER IT Command word: Describe. Worth 2 marks, so plan before writing.
Question 1 · mark scheme
2 marks available. Award a mark for each point made.
▸ 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.
Question 2 · 2 marks · State
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“Give one example of a transverse wave and one example of a longitudinal wave.” |
HOW TO ANSWER IT Command word: State. Worth 2 marks, so plan before writing.
Question 2 · mark scheme
2 marks available. Award a mark for each point made.
▸ 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.
Question 3 · 3 marks · Describe
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“Describe how a longitudinal wave, such as a sound wave, travels through air. Use the words compression and rarefaction.” |
HOW TO ANSWER IT Command word: Describe. Worth 3 marks, so plan before writing.
Question 3 · mark scheme
3 marks available. Award a mark for each point made.
▸ 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.
Question 4 · 3 marks · Describe
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“A cork floats on water. Ripples pass it. Describe what happens to the cork and explain what this shows about the wave.” |
HOW TO ANSWER IT Command word: Describe. Worth 3 marks, so plan before writing.
Question 4 · mark scheme
3 marks available. Award a mark for each point made.
▸ 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.
Question 5 · 3 marks · Explain
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“Explain why sound cannot travel through a vacuum but light can.” |
HOW TO ANSWER IT Command word: Explain. Worth 3 marks, so plan before writing.
Question 5 · mark scheme
3 marks available. Award a mark for each point made.
▸ 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.