Ultrasound and seismic waves - Teacher Slides.pptx

AQA GCSE PHYSICS · PAPER 2 · HIGHER TIER ONLY

Ultrasound and seismic waves

Waves

Lesson 6 of 12

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Warm-up

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Lesson 6 of 12

Answer each one, then check.

1

What is an echo?

2

What is the speed equation?

3

What is ultrasound?

4

What causes an earthquake?

5

Is a P-wave longitudinal or transverse?

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Warm-up - Answers

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Lesson 6 of 12

1

What is an echo?

A reflected sound

2

What is the speed equation?

v = s ÷ t

3

What is ultrasound?

Sound with frequency above 20 kHz

4

What causes an earthquake?

Movement of the Earth's tectonic plates

5

Is a P-wave longitudinal or transverse?

Longitudinal

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Learning Objectives

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Lesson 6 of 12

1

Explain how ultrasound is partially reflected at boundaries and used for imaging.

2

Use the time taken for an echo to calculate a distance.

3

Describe P-waves and S-waves and how they provide evidence about the Earth's structure.

4

Describe echo sounding.

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Waves

Lesson 6 of 12

DETECTION AND EXPLORATION

Ultrasound waves are partially reflected when they meet a boundary between two media. The time taken for the echo to return can be used to work out how far away the boundary is.

Seismic waves from earthquakes (P-waves and S-waves) give evidence of the structure of the Earth.

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Echo Sounding

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The pulse travels to the boundary and back.

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Seismic Waves and the Earth

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S-waves cannot pass through the liquid outer core.

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P-waves and S-waves

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P-WAVES

• Longitudinal seismic waves.

• Travel through solids and liquids.

• Travel faster than S-waves.

• Speed changes between solids and liquids.

S-WAVES

• Transverse seismic waves.

• Cannot travel through liquids.

• Travel more slowly.

• Stopped by the liquid outer core.

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Echo Sounding

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Lesson 6 of 12

A ship sends an ultrasound pulse down and receives the echo 0.40 s later. The speed of sound in sea water is 1500 m/s. Calculate the depth.

1

Distance there and back

1500 × 0.40 = 600 m

2

Depth is half of this

600 ÷ 2 = 300 m

ANSWER

300 m

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Medical Ultrasound

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Lesson 6 of 12

An ultrasound pulse is reflected from a boundary inside the body after 0.000060 s. The speed in tissue is 1500 m/s. Calculate the depth of the boundary.

1

Total distance

1500 × 0.000060 = 0.090 m

2

Depth

0.090 ÷ 2 = 0.045 m = 4.5 cm

ANSWER

4.5 cm

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Evidence for the Core

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Lesson 6 of 12

Explain how S-waves give evidence that part of the Earth's core is liquid.

1

S-waves

Cannot travel through liquids

2

Observation

They are not detected on the far side of the Earth

3

Conclusion

Part of the core (the outer core) must be liquid

ANSWER

S-waves are blocked by the outer core, so it must be liquid.

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Uses

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Lesson 6 of 12

Other examples.

Medical imaging

Ultrasound scans of foetuses and organs are safe (non-ionising).

Industrial imaging

Ultrasound detects cracks in metal.

Echo sounding

Used for water depth and to detect fish or shipwrecks.

Seismology

New evidence from seismic waves led to discoveries about parts of the Earth that cannot be observed directly.

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Key Terms

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Lesson 6 of 12

Ultrasound

Sound with frequency above 20 kHz.

Echo

A reflection of a sound wave.

Seismic wave

A wave produced by an earthquake.

P-wave

A longitudinal seismic wave.

S-wave

A transverse seismic wave that cannot travel through liquids.

Echo sounding

Using reflected sound to find depth.

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Lesson 6 of 12

YOUR TASK

Depth Finder

10 minutes

A boat sends out ultrasound and hears the echo after 0.20 s (speed 1500 m/s). Calculate the depth of the water. Explain why the time must be halved.

1

Use s = vt.

2

Halve the distance.

WHAT A GOOD ANSWER SHOWS

Distance there and back = 1500 × 0.20 = 300 m; depth = 150 m. The pulse travels to the bottom and back.

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Can I...?

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Lesson 6 of 12

Define ultrasound.

Explain echo timing.

Calculate depth by echo.

Describe P-waves.

Describe S-waves.

Explain the liquid core.

Give uses of ultrasound.

Explain why the time is halved.

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Summary & Exam Focus

Ultrasound is partially reflected at boundaries.

Depth = speed × time ÷ 2.

P-waves: longitudinal; S-waves: transverse, not through liquids.

Seismic evidence shows a liquid outer core.

EXAM FOCUS

A ship sends out ultrasound and receives the echo 0.40 s later. The speed is 1500 m/s. Calculate the depth of the sea. (3 marks)

Distance there and back, then halve.

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Exam Practice: Ultrasound and seismic waves

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Lesson 6 of 12

Answer all questions. Use the mark allocation as a guide to how much to write. · 16 minutes

Question 1 · 3 marks · Calculate

A ship sends a pulse of ultrasound towards the sea bed and detects the echo 0.40 s later. The speed of sound in sea water is 1500 m/s…

Question 2 · 3 marks · Explain

Explain how ultrasound waves can be used to produce an image of an organ in the body.

Question 3 · 4 marks · Explain

S-waves cannot travel through the Earth's outer core. Explain what this tells scientists about the outer core, and how the properties of…

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Exam Practice: Ultrasound and seismic waves (cont.)

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Lesson 6 of 12

Question 4 · 2 marks · State

State two differences between P-waves and S-waves.

Question 5 · 3 marks · Explain

Suggest why ultrasound is used rather than X-rays to scan an unborn baby.

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Question 1 · 3 marks · Calculate

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Lesson 6 of 12

“

A ship sends a pulse of ultrasound towards the sea bed and detects the echo 0.40 s later. The speed of sound in sea water is 1500 m/s. Calculate the depth of the sea at this point.

HOW TO ANSWER IT

Command word: Calculate. Worth 3 marks, so plan before writing.

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Question 1 · mark scheme

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Lesson 6 of 12

3 marks available. Award a mark for each point made.

Correct substitution

1 mark

600 m

1 mark

300 m (halved)

1 mark

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Question 2 · 3 marks · Explain

Waves

Lesson 6 of 12

“

Explain how ultrasound waves can be used to produce an image of an organ in the body.

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

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Question 2 · mark scheme

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Lesson 6 of 12

3 marks available. Award a mark for each point made.

Partially reflected at boundaries

1 mark

Time taken for echoes measured

1 mark

Distance calculated and used to form an image

1 mark

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Question 3 · 4 marks · Explain

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Lesson 6 of 12

“

S-waves cannot travel through the Earth's outer core. Explain what this tells scientists about the outer core, and how the properties of P-waves give further evidence about the Earth's structure.

HOW TO ANSWER IT

Command word: Explain. Worth 4 marks, so plan before writing.

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Question 3 · mark scheme

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Lesson 6 of 12

4 marks available. Award a mark for each point made.

S-waves cannot travel through liquids

1 mark

So the outer core is liquid

1 mark

P-waves travel through solids and liquids at different speeds

1 mark

Changes show boundaries between layers

1 mark

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Question 4 · 2 marks · State

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Lesson 6 of 12

“

State two differences between P-waves and S-waves.

HOW TO ANSWER IT

Command word: State. Worth 2 marks, so plan before writing.

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Question 4 · mark scheme

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Lesson 6 of 12

2 marks available. Award a mark for each point made.

Longitudinal and transverse

1 mark

A second difference

1 mark

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Question 5 · 3 marks · Explain

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Lesson 6 of 12

“

Suggest why ultrasound is used rather than X-rays to scan an unborn baby.

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

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Question 5 · mark scheme

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Lesson 6 of 12

3 marks available. Award a mark for each point made.

Ultrasound non-ionising

1 mark

X-rays ionising

1 mark

Could damage cells of the baby

1 mark

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