Topicm8b85f5d88d172742_1528449000663_0Topic

Law of light reflection

Levelm8b85f5d88d172742_1528449084556_0Level

Second

Core curriculumm8b85f5d88d172742_1528449076687_0Core curriculum

IX. Optics. The student:

2) describes the phenomenon of reflection off a flat surface and a spherical surface.

Timingm8b85f5d88d172742_1528449068082_0Timing

45 minutes

General learning objectivesm8b85f5d88d172742_1528449523725_0General learning objectives

Describes the law of light reflection.

Key competencesm8b85f5d88d172742_1528449552113_0Key competences

1. Recognises the phenomenon of light reflection.
2. Explains the phenomenon of light reflection.

Operational (detailed) goalsm8b85f5d88d172742_1528450430307_0Operational (detailed) goals

The student:
- recognizes the phenomenon of light reflection,
- explains the law of light reflection.

Methodsm8b85f5d88d172742_1528449534267_0Methods

1. Discussion.
2. Experiment.

Forms of workm8b85f5d88d172742_1528449514617_0Forms of work

1. Individual work.
2. Group work.

Lesson stages

Introductionm8b85f5d88d172742_1528450127855_0Introduction

The teacher conducts discussion with students about:

What types of surfaces reflect light best?

During brainstorming students formulate the definition of a mirror.

Definition:
A mirror is a smooth surface that reflects light.
A plane mirror is a flat, polished surface which in ideal case neither absorbs nor scatters light, but only reflects it.m8b85f5d88d172742_1527752263647_0A mirror is a smooth surface that reflects light.
A plane mirror is a flat, polished surface which in ideal case neither absorbs nor scatters light, but only reflects it.

Procedurem8b85f5d88d172742_1528446435040_0Procedure

Students already know that light propagates in straight lines. They prove experimentally in which direction the light reflected off the smooth polished surface propagates. The students work in small groups.

Experiment

Research problem:
What ist the direction of light rays reflected off a smooth polished surface?

Hypothesis: 
The angle of incidence and the angle of reflection are equal.

Materials: 
- laser pointer or a lamp with an aperture, 
- protractor, 
- scissors, 
- plane mirror.

Instruction:

1. According to the instruction prepare and cut off four diagrams. Place the plane mirror in a position shown in the picture. Put the light beam exactly along the drawn arrow. Then, as precisely as possible, draw using a pencil the path of a reflected ray. Repeat that for all four diagrams.
2. Fold every diagram in a way that the both incident ray and the reflected ray lie on top of each other. Unfold and flatten the diagrams and place them next to each other. Note down your observations.
3. Measure the angle between the incident ray and the fold line as well as the angle between the reflected ray and the fold line. Mark them as α and β and note their values into your exercise book.
4. Attach the diagrams to your exercise book.

[Illustration 1]

Conclusion:

The angle of incidence and the angle of reflection are equal.

Students generalize the results obtained in the experiment. They formulate the law of reflection and present it graphically.

Task 1
Draw a diagram summarizing the experiment. 
Formulate the law of light reflection. Make captions on every element of the diagram.

Solution:

[Illustration 2]

The angle of incidence and the angle of reflection are equal. The incident ray, the reflected ray and the normal in the point of reflection all lie in the same plane.

Students practice the application of the law of reflection.

The teacher reminds students about the use of a protractor and accurate drawing.

Task 2
The drawings show two mirrors in different settings. Draw the path of the light ray after reflection off their surfaces for each case. Mark normal at each point of reflection. Use a protractor.

[Illustration 3]

Solution:

[Illustration 4]

The teacher discusses with students the application of the law of reflection in situations known from everyday life.

Students give examples of the application of the law of reflection.

Task 3
A simple periscope using two plane mirrors inclined at 45° allows observation from behind a high wall or an obstacle. Draw the path of a light ray in a periscope as it travels from an object into an observer’s eye.

Solution:

[Illustration 5]

Students solve the problem of setting mirrors in case of a known path of light rays.

Task 4
The boxes contain mirrors that direct the light rays as shown in the picture. Draw their location on the given schemes. Complete the path of light rays.

[Illustration 6]

Lesson summarym8b85f5d88d172742_1528450119332_0Lesson summary

Law of light reflection.

The angle of incidence and the angle of reflection are equal. The incident ray, the reflected ray and the normal in the point of reflection all lie in the same plane.m8b85f5d88d172742_1527752256679_0The angle of incidence and the angle of reflection are equal. The incident ray, the reflected ray and the normal in the point of reflection all lie in the same plane.

Selected words and expressions used in the lesson plan

reflectionreflectionreflection

incident rayincident rayincident ray

reflected rayreflected rayreflected ray

angle of reflectionangle of reflectionangle of reflection

angle of incidenceangle of incidenceangle of incidence

surfacesurfacesurface

rayrayray

normal (line)normal (line)normal (line)

equalequalequal