Visible light and colour - Teacher Slides.pptx

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Visible light and colour

Waves

Lesson 11 of 12

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Warm-up

Waves

Lesson 11 of 12

Answer each one, then check.

1

What colours make up white light?

2

What is reflection?

3

What is absorption?

4

What is transparent?

5

What is opaque?

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Warm-up - Answers

Waves

Lesson 11 of 12

1

What colours make up white light?

The colours of the rainbow

2

What is reflection?

A wave bouncing off a surface

3

What is absorption?

A wave's energy being taken in by a material

4

What is transparent?

Lets light pass through with no scattering

5

What is opaque?

Does not let light through

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Learning Objectives

Waves

Lesson 11 of 12

1

State that each colour of visible light has its own narrow band of wavelength and frequency.

2

Distinguish specular reflection from diffuse reflection.

3

Explain how colour filters work.

4

Explain why an opaque object has a particular colour.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Waves

Lesson 11 of 12

COLOUR

Each colour within the visible spectrum has its own narrow band of wavelength and frequency. The colour of an opaque object depends on which wavelengths it reflects most strongly.

Wavelengths that are not reflected are absorbed. If all wavelengths are reflected equally the object looks white; if all are absorbed it looks black.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Filters and Coloured Objects

Waves

Lesson 11 of 12

Colour comes from which wavelengths are reflected or transmitted.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Specular or Diffuse Reflection?

Waves

Lesson 11 of 12

SPECULAR REFLECTION

• From a smooth surface such as a mirror.

• Reflected in a single direction.

• Forms a clear image.

DIFFUSE REFLECTION

• From a rough surface such as paper.

• Scattered in many directions.

• No clear image.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Objects and Colours

Waves

Lesson 11 of 12

What you see.

Object

In white light

Why

Red shirt

Red

Reflects red, absorbs other colours

Green leaf

Green

Reflects green, absorbs the rest

White paper

White

Reflects all colours equally

Black cloth

Black

Absorbs all colours

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

A Colour Filter

Waves

Lesson 11 of 12

White light passes through a green filter. What colour emerges?

1

Filter

Transmits green and absorbs the other wavelengths

2

Light that emerges

Green

ANSWER

Green light.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Two Filters

Waves

Lesson 11 of 12

White light passes through a red filter and then a blue filter. What emerges?

1

Red filter

Transmits only red

2

Blue filter

Absorbs red and transmits blue

3

Result

No light

ANSWER

No light emerges (black).

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Coloured Light on an Object

Waves

Lesson 11 of 12

A red shirt is illuminated with green light only. What colour does it look?

1

Red shirt

Reflects red but absorbs green

2

Green light

There is no red light to reflect

3

Result

The shirt looks black

ANSWER

Black.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Key Terms

Waves

Lesson 11 of 12

Transparent, translucent and opaque.

Transparent

Transmits light; you can see clearly through it.

Translucent

Transmits light but scatters it; you cannot see a clear image.

Opaque

Does not transmit light.

Filters

Absorb certain wavelengths and transmit others.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Key Terms

Waves

Lesson 11 of 12

Specular reflection

Reflection from a smooth surface in a single direction.

Diffuse reflection

Reflection from a rough surface in many directions.

Colour filter

Material that transmits some wavelengths and absorbs others.

Transparent

Lets light pass through with no scattering.

Translucent

Lets light through but scatters it.

Opaque

Does not let light through.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Waves

Lesson 11 of 12

YOUR TASK

Predict the Colour

10 minutes

What colour does a blue book look in (a) white light (b) red light? What does a white page look in blue light?

1

What wavelengths does it reflect?

2

What light is available?

WHAT A GOOD ANSWER SHOWS

(a) Blue. (b) Black, because it absorbs red. A white page in blue light looks blue.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Can I...?

Waves

Lesson 11 of 12

State that colours have wavelength bands.

Explain specular reflection.

Explain diffuse reflection.

Explain filters.

Explain object colour.

Explain black and white.

Define transparent, translucent, opaque.

Predict colours under filters.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Summary & Exam Focus

Colours: narrow bands of wavelength and frequency.

Smooth: specular; rough: diffuse.

Filters transmit some wavelengths and absorb others.

Object colour from the wavelengths it reflects.

EXAM FOCUS

Explain why a red book looks red in white light. (2 marks)

Reflects red, absorbs other colours.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Exam Practice: Visible light and colour

Waves

Lesson 11 of 12

Answer all questions. Use the mark allocation as a guide to how much to write. · 13 minutes

Question 1 · 2 marks · Explain

A red book looks red in white light. Explain why.

Question 2 · 2 marks · Describe

Describe the difference between specular reflection and diffuse reflection.

Question 3 · 3 marks · Explain

White light passes through a green filter onto a white screen. Explain what colour the screen looks. Then explain what happens if the light…

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Exam Practice: Visible light and colour (cont.)

Waves

Lesson 11 of 12

Question 4 · 3 marks · Explain

A blue shirt is seen in red light. Explain why it looks black.

Question 5 · 2 marks · State

Explain the difference between a transparent and a translucent material.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 1 · 2 marks · Explain

Waves

Lesson 11 of 12

“

A red book looks red in white light. Explain why.

HOW TO ANSWER IT

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

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 1 · mark scheme

Waves

Lesson 11 of 12

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

Reflects red

1 mark

Absorbs other colours

1 mark

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 2 · 2 marks · Describe

Waves

Lesson 11 of 12

“

Describe the difference between specular reflection and diffuse reflection.

HOW TO ANSWER IT

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

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 2 · mark scheme

Waves

Lesson 11 of 12

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

Specular: smooth surface, one direction

1 mark

Diffuse: rough surface, scattered

1 mark

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 3 · 3 marks · Explain

Waves

Lesson 11 of 12

“

White light passes through a green filter onto a white screen. Explain what colour the screen looks. Then explain what happens if the light from the green filter goes through a red filter.

HOW TO ANSWER IT

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

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 3 · mark scheme

Waves

Lesson 11 of 12

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

Green filter transmits green

1 mark

Screen looks green

1 mark

Red filter absorbs green: no light

1 mark

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 4 · 3 marks · Explain

Waves

Lesson 11 of 12

“

A blue shirt is seen in red light. Explain why it looks black.

HOW TO ANSWER IT

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

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 4 · mark scheme

Waves

Lesson 11 of 12

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

Shirt reflects blue

1 mark

Absorbs red light

1 mark

So no light reflected: looks black

1 mark

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 5 · 2 marks · State

Waves

Lesson 11 of 12

“

Explain the difference between a transparent and a translucent material.

HOW TO ANSWER IT

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

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 5 · mark scheme

Waves

Lesson 11 of 12

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

Transparent: clear view

1 mark

Translucent: light scattered

1 mark

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