Reflection (Reflection ( 反射反射 ))

incident ray reflected ray

plane mirror

angle of incidence

angle of reflection

normalReflection of Light (Reflection of Light ( 光的反射光的反射 ))

3

Incident Rays

(入射線 )

The light ray moving towards the mirror

Reflected Rays

(反射線 )

The light ray moving out of the mirror

Normal

(法線 )

The line perpendicular (垂直 ) to the mirror

Angle of incidence

(入射角 )

The angle between the incident ray and the normal.

Angle of reflection

(反射角 )

The angle between the reflected rays and the normal.

incidentray

reflectedray

Laws of reflection:

The angle of

reflection r

equal to

of incidence i.

plane mirror

i r

1.

is

the angle

normalvertical plane

Laws of reflectionLaws of reflection ((反射定律反射定律 ))

i = r

Laws of reflection:

The incident ray,

the reflected ray

and the normal

all lie in the sameplane.

incidentray

reflectedray

normal

plane mirror

vertical plane2.

6

i = 0 r = 0 air

mirror

When the angle of incidence equals to zero (i = 0) , the angle of reflection is also zero (r = 0).

7

8

40°

40°

60°

60°

30°

30°

45°

45°

9

5.3 Experiment (實驗 )

電源

光箱

量角器

平面鏡

10

i / 0 30 45 60 75

r /

Conclusion (結論 )

The angle of incidence is ____________ the angle of reflection.

11

i / 0 30 45 60 75

r / 0 30 45 60 75

Conclusion (結論 )

The angle of incidence is _equal to_ the angle of reflection.

Will the reflected rays remain parallel (平行 ) after reflection?

Regular reflection Regular reflection ((單向反射單向反射 ))

same i same r The reflected rays are therefore parallel.

i i ir r r

parallel incident rays parallel reflected rays

plane mirror

Each light ray obeys the laws of reflection.

For flat ( 平 ) and smooth ( 滑 ) surface,

plane mirror

Regular reflection (單向反射 ) occurs at:

The following reflecting surfaces can form clear images due to regular reflection.

a calm water surfacemetal surface

For rough (粗糙 ) surface,

i1i2

i3

r1 r2

r3

rough surface

parallel incident rays

reflected rays are not parallel

Each light ray obeys the laws of reflection.different i different r

Diffuse reflectionDiffuse reflection ((漫反射漫反射 ))

Diffuse reflection occurs at a rough surface (e.g. a piece of paper).

e.g. a piece of paper

Lateral inversion (Lateral inversion ( 橫向倒置橫向倒置 ))

Mirror images are laterally inverted.

The laterally inverted words on an ambulance (救護車 )

the object image formed by the plane mirror

An image formed by a plane mirror is

1. same size as the object,

2. laterally inverted. ((橫向倒置橫向倒置 ))

3. same distance

21

22

23

Uses of plane mirrors (平面鏡的應用 )

rear-view mirrors (倒後鏡 )

24

Explain why the Chinese characters 救護車 are printed in the special way as shown.

25

So that the driver of the car in front of the ambulance can see the Chinese characters 救護車 without lateral inversion.

PeriscopePeriscope ((潛望鏡潛望鏡 ))

A periscope consists of two mirrors The mirrors make an angle of 45 with the

line joining them.

Periscopes are used in a double-deckers (雙層巴士 )

28

Periscope (潛望鏡 ) used in submarine (潛水艇 ).

29

Plane mirrors used in interior design (室內設計 ).

30

Plane mirror used by dentist (牙醫 ).

31

In Figure 5.4, draw ONE light ray from the head of the object to the eye after reflection from the two mirrors.

32

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Homework: Assignment Book 1. Chapter 5 Q.1 – Q.8 (p.7-9)

2. Deadline: