Reflection of waves.pptx

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Reflection of waves

Waves

Lesson 3 of 12

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Warm-up

Waves

Lesson 3 of 12

Answer each one, then check.

1

What is a ray?

2

What is a mirror?

3

What is a normal?

4

What is an angle?

5

Name a material that light passes through.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Warm-up - Answers

Waves

Lesson 3 of 12

1

What is a ray?

A straight line showing the path of light

2

What is a mirror?

A smooth shiny surface that reflects light

3

What is a normal?

A line at right angles to a surface

4

What is an angle?

A measure of turn, in degrees

5

Name a material that light passes through.

Glass or water

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Learning Objectives

Waves

Lesson 3 of 12

1

Describe reflection, absorption and transmission of waves at a boundary.

2

State and apply the law of reflection.

3

Construct ray diagrams showing reflection at a surface.

4

Describe how to investigate the reflection of light by different surfaces.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Waves

Lesson 3 of 12

REFLECTION

Waves can be reflected, absorbed or transmitted at the boundary between two materials. The angle of incidence equals the angle of reflection.

Angles are measured between the ray and the normal, a line at right angles to the surface at the point where the ray strikes it.

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The Law of Reflection

Waves

Lesson 3 of 12

Measure both angles from the normal.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Required Practical 9: Reflection with a Ray Box

Waves

Lesson 3 of 12

Draw the normal, then measure both angles from it.

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How to Draw a Reflection Ray Diagram

Waves

Lesson 3 of 12

Follow the steps.

1

Draw the mirror

A straight line.

2

Draw the normal

A dashed line at 90° to the mirror at the point of incidence.

3

Draw the incident ray

Toward the point, with an arrow.

4

Measure the angle of incidence

Between the ray and the normal.

5

Draw the reflected ray

At the same angle on the other side of the normal, with an arrow.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

What Happens at a Boundary

Waves

Lesson 3 of 12

Waves can do three things.

Effect

What it means

Example

Reflection

The wave bounces off the surface

Light from a mirror; an echo

Absorption

The wave's energy is transferred to the material

Black paper absorbs light and warms up

Transmission

The wave passes through the material

Light passing through glass

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Finding Angles

Waves

Lesson 3 of 12

A ray strikes a plane mirror so that the angle between the ray and the mirror surface is 50°. Find the angle of reflection.

1

Angle to the normal

90°− 50°= 40°

2

Law of reflection

Angle of reflection = angle of incidence

ANSWER

40°, measured from the normal.

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Practical Tips

Waves

Lesson 3 of 12

Get accurate results.

Narrow beam

Use a single slit so the ray is thin.

Mark the ray

Put a cross on the ray at two points and draw a line through them.

Repeat

Measure for several angles of incidence.

Conclusion

The angle of incidence equals the angle of reflection.

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Key Terms

Waves

Lesson 3 of 12

Reflection

When a wave bounces off a surface.

Absorption

When a wave's energy is taken in by a material.

Transmission

When a wave passes through a material.

Normal

A line at right angles to a surface.

Angle of incidence

The angle between the incident ray and the normal.

Angle of reflection

The angle between the reflected ray and the normal.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Waves

Lesson 3 of 12

YOUR TASK

Reflect It

10 minutes

A ray hits a mirror at an angle of incidence of 35°. Draw a ray diagram. State the angle between the reflected ray and the mirror surface.

1

Draw the normal first.

2

Mirror the angle.

WHAT A GOOD ANSWER SHOWS

The angle of reflection is 35°. The angle to the mirror is 90° − 35° = 55°.

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Can I...?

Waves

Lesson 3 of 12

Define reflection.

Define absorption and transmission.

State the law of reflection.

Draw a normal.

Measure angles from the normal.

Draw a reflected ray.

Describe the practical.

Find an angle to the mirror.

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Summary & Exam Focus

Angle of incidence = angle of reflection.

Angles measured from the normal.

Reflection, absorption, transmission.

Use a ray box, mirror and protractor.

EXAM FOCUS

State the law of reflection. (1 mark)

The angle of incidence equals the angle of reflection.

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