Starter quiz
- Which of the following images correctly shows light rays coming from a lamp?
- Which of the following units are angles measured in?
- metres
- degrees ✓
- millimetres
- millilitres
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What is the size of the marked angle?- 50°
- 90° ✓
- 100°
- 180°
- 360°
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- The size of a full turn is ______°.
- '360' ✓
- Which of the following pieces of equipment is used to measure angles?
- ruler
- compass
- protractor ✓
- set square
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What is the size of the marked angle between the two lines in the image?- 37° ✓
- 43°
- 143°
- 157°
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Exit quiz
- Match the following key terms to their definitions.
- normal⇔An imaginary line drawn at 90° to the point of reflection at a mirror. ✓
- incident ray⇔An arrow showing the direction of light before it hits a mirror. ✓
- reflected ray⇔An arrow showing the direction of light after it hits a mirror. ✓
- The diagrams show a light ray reflecting from a mirror. In which diagram is the angle of incidence marked?
- Which of the following is the first law of reflection?
- angle of reflection > angle of incidence
- angle of reflection = angle of incidence ✓
- angle of reflection + angle of incidence = 90°
- angle of reflection + angle of incidence = 180°
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- Which of the following are the second and third laws of reflection?
- The incident ray and the reflected ray are on the same side of the normal.
- The incident ray and the reflected ray are on opposite sides of the normal. ✓
- The incident ray, reflected ray and normal are on one plane (flat surface). ✓
- The incident ray, reflected ray and normal are on different planes.
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- A pupil investigates reflection of light by a mirror. They decrease the angle of incidence. Which of the following describes what happens to the angle of reflection?
- It increases.
- It decreases. ✓
- It stays the same.
- It is impossible to predict.
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- Why is it unlikely that measurements of the angle of reflection are exactly equal to the angle of incidence?
- The mirror may not be exactly aligned with the mirror line on the diagram. ✓
- The surface of the mirror may not be flat.
- A sharp pencil line is difficult to see under a protractor.
- A protractor measures to the nearest degree. ✓
- Rays of light from a ray lamp are wider than a sharp pencil line. ✓
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Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- Light travelling in one direction (along a ray) that hits a mirror reflects (bounces off the mirror) in one direction.
- The ‘normal’ is an imaginary line drawn at 90° to the point of reflection.
- The angles of incidence and reflection are measured to the normal.
- The angle of reflection is always equal to the angle of incidence, the other side of the normal.
- On a graph, a line of best fit highlights the main pattern of the data, ignoring small errors.
Common misconception
Some pupils think that a ray of light can reflect off at an angle different to that at which it hits a plane mirror and perhaps in several directions.
Give pupils practical experience of measuring the angles at which light reflects off a plane mirror to confirm the correct rules; share results to confirm; and discuss potential sources of error that may lead to small discrepancies.
Keywords
Protractor - a device used to measure angles
Normal - another way of saying ‘at 90°’ - a ‘normal line’ is at 90° to a surface
Reflect - to reflect off a surface means to hit the surface and ‘bounce’ off
Incident - an adjective meaning 'incoming'
Angle of incidence - the angle between the incident ray and the normal when light hits a mirror
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