Transverse and longitudinal waves.pptx

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Transverse and longitudinal waves

Waves

Lesson 1 of 12

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Warm-up

Waves

Lesson 1 of 12

Answer each one, then check.

1

What do waves transfer?

2

Give an example of a wave.

3

What is a medium?

4

What is a vibration?

5

What do sound waves travel through?

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Warm-up - Answers

Waves

Lesson 1 of 12

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

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Learning Objectives

Waves

Lesson 1 of 12

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.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Waves

Lesson 1 of 12

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.

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Transverse and Longitudinal Waves

Waves

Lesson 1 of 12

The direction of vibration compared with travel is the key difference.

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Transverse or Longitudinal?

Waves

Lesson 1 of 12

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.

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Evidence That the Wave Travels

Waves

Lesson 1 of 12

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.

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Sound in Air

Waves

Lesson 1 of 12

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.

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Key Points

Waves

Lesson 1 of 12

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.

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Key Terms

Waves

Lesson 1 of 12

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.

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Waves

Lesson 1 of 12

YOUR TASK

Wave Types

8 minutes

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?

WHAT A GOOD ANSWER SHOWS

(a) Transverse (b) Longitudinal (c) Transverse (d) Transverse.

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Can I...?

Waves

Lesson 1 of 12

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.

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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)

Direction of vibration relative to the direction of travel.

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