Reflection of light

2. ObjectivesObjectives
•Define the terms normal, angle of
incidence and angle of reflection
•State the angle of incidence is equal
to the angle of reflection and use
this principle in construction,
measurements and calculations.

3. Nature of lightNature of light
•A form of energy which enables us to see
•It travels in straight line
•It travels at a very high speed
(3.0 x 10
8
ms
-1
) in vacuum.
•It is emitted by luminous sources such as
SUN, STARS, CANDLES, SUN, STARS, CANDLES,
LAMPS, LAMPS, etc.etc.

4. Nature of lightNature of light
•White light is a mixture of seven White light is a mixture of seven
different colours namely Red, different colours namely Red,
Orange , Yellow, Green, Blue, Orange , Yellow, Green, Blue,
Indigo, Violet.Indigo, Violet.
•Light is a transverse wave and Light is a transverse wave and
forms part of the electromagnetic forms part of the electromagnetic
spectrumspectrum..

5. Light rayLight ray
•The path along which light energy travels
is called a RAY.
•It is represented by a straight line with
an arrow to show its direction of motion.

6. Beam of Light Beam of Light
•A beam of light is a bundle of light rays.
Parallel beam Converging
beams
Diverging beams

7. Theabruptchangeinthe

directionofpropagationof

lightraysthatstrikethe

boundarybetweendifferent
.
medium

Reflection of lightReflection of light

8. plane
p
normal
u
normal
center

Animaginaryline
perpendicular
toasurface
.
wherethereflectionoccurs
Normal :

9. Reflection of Light(1)Reflection of Light(1)
i r
Incident
ray
normal
plane mirror
( )
Theraystrikingthesurface incomingray
( )
Therayreflectedfromthesurface outgoingray
Reflected
ray

10. Reflection of Light(2)Reflection of Light(2)

Theanglebetweenincidentrayandnormal

Theanglebetweenreflectedrayandnormal
i r
Incident
ray
normal
plane mirror
Reflected
ray
Ð i =
angleof incidence
Ð r =
angleof reflection
Ð i Ð r

11. :
LawsofReflection
•Law 1: The incident ray, the reflected
ray and the normal at the point of
incidence all lie on the same plane.
•Law 2: The angle of incidence is equal
to the angle of reflection.
Angle i = Angle r

12. The diagram shows a ray of light being The diagram shows a ray of light being
reflected by a plane mirror MN.reflected by a plane mirror MN.
Which one of the following statements is Which one of the following statements is
completely correct ?completely correct ?
A LP is the incident ray, PR A LP is the incident ray, PR
is the reflected ray and x is is the reflected ray and x is
the angle of reflection.the angle of reflection.
B LP is the reflected ray, x is the angle ofB LP is the reflected ray, x is the angle of
incidence and y is the angle of reflection.incidence and y is the angle of reflection.
C LP is the incident ray, x is the angle ofC LP is the incident ray, x is the angle of
incidence and y is the angle of reflection.incidence and y is the angle of reflection.
D PQ is the normal, x = y, and PR is the D PQ is the normal, x = y, and PR is the
incident ray. incident ray.
C
1
Example
1
Example

13. Reflectionby

theplanemirror
i r
Plane mirror
Note: Normal always perpendicular
to the mirror
i r
Incident
ray
normal
plane mirror
Reflected
ray
Ð i =
angleof incidence
Ð r =
angleof reflection
Ð i Ð
r

14. 2
Example
2
Example
Angle incidence = 90
0
- 40
0

= 50

0
Angle of reflection = Angle of incidence
= 50
0

The diagram shows a ray of light reflected in a
plane mirror.
What is the angle of reflection?

15. 3
Example
3
Example
Angle of incidence = 90
0
- 10
0
= 80
0



Angle b = 10
0
A ray of light is reflected from a plane
mirror as shown in the diagram below:
•What is the angle of
incidence?
•What is the size of
the angle marked b?

16. The diagram shows a ray of light striking a
plane mirror. What is the angle of
incidence if the total angle between the
incident ray and reflected ray is 70°?
4
Example
4
Example
Angle of incidence
= Angle of reflection
= 70
0
/ 2
= 35
0

17. 5
Example
5
Example
In the figure below, ray AB will be reflected twice.
Find the angle of reflection in the second reflection.
Copy the figure and complete the path of the ray.
C
30
0
r
1
i
2
r
2
angle r
1
= 30
0
; angle r
2
= angle i
2

= 90
0
- 30
0
= 60
0
u
30
0
A
B

18. MIRROR IMAGE(1)
BIKEBOOK
BOXCHOKE
DECIDECHICK

19. MIRROR IMAGE(1)
BIKEBOOK
BOXCHOKE
DECIDECHICK

20. MIRROR IMAGE(2)
SPEEDPOLES
BEDLIGHT
POWERCHECK

21. MIRROR IMAGE(2)
SPEEDPOLES
BEDLIGHT
POWERCHECK

22. Formationofimagesona
:
planemirror
•To the eye, all the reflected rays
appear to have come from I, the
image.
•Thus, the image formed is virtual.

23. RealandVirtualImages
•A real image is one which can be
formed on a screen.
•It is produced by ray that converge
at the position of the image.
•A virtual image is one which cannot
be formed on a screen.
•It is produced by reflection of light.

24. Imageformedby
:
PlaneMirror
•It is virtual.
•It is upright.
•It is lateral inverted.
•It has the same size as the object.
•Distance of the image from the mirror
is equal to the distance of the object
from the mirror.

25. A person stands 2.0 m in front of the mirror as
shown. How far from the person is her image?
ExampleExample
Image is 4.0 m
from the
person.

26. The diagram shows two divergent rays of
light from an object O being reflected from
a plane mirror.
At which position will the image be
formed?
ExampleExample
BB

27. i
r
Note:
i = r
object image
normal
eye
object
image
mirror
mirror

Raydiagramshowingthe

formationofanimage

28. Imageformedby

theplanemirror

29. Plane mirror
Regular reflection
Black surface
Absorption
Irregular surface
Diffuse reflection
Glass block
Transmission
Glass
Various cases of rays:

30. Two types of Reflection:
1. Regular reflection ( Image formed
by plane, a smooth surface, image
can see by our eyes)

31. 2. Diffuse reflection ( Image formed by
white paper, with rough surface. Image
formed usually not clear)
(continue …)

32. mirror
mirror
:
Periscope
Periscopes are used
in submarines so
that people below
the water surface
can see what is
happening above.
(Type 1)

33. prism
prism
Periscopes are used
in submarines so
that people below
the water surface
can see what is
happening above.
:
Periscope
(Type 2)

34. Periscope: [Cont.]
•The periscope consists of two parallel plane
mirrors (or prism) .
•Could you guess at what angle should each
mirror (or prism) be placed ?
•Why ?
•Which type of periscope is better ? Mirror or
prism ? Why ?

35. GCE O-LevelGCE O-Level
Past Examination PaperPast Examination Paper
Science (Physics)

36. November 1989
8.Which of the following correctly describes the image
formed in a plane mirror when compared to the
object?
A virtualsmaller
B virtualsame size
C virtuallarger
D real same size
B

37. Nov 1990
6. An object ‘O’ is placed in front of a plane mirror.
A viewer looks into the mirror as shown in the
diagram.
In which position is the image of O formed?
B

38. Nov 1991
10. The diagram shows a ray of light being
reflected by a plane mirror MN.
Which one of the following statements is
completely correct ?
A LP is the incident
ray, PR is the
reflected ray and
x is the angle of reflection.
B LP is the reflected ray, x is the angle of
incidence and y is the angle of
reflection.
C LP is the incident ray, x is the angle of
incidence and y is the angle of
reflection.
D PQ is the normal, x = y, and PR is the
incident ray.
C

39. 4. The diagram below shows the position I of the image
formed by a plane mirror of an object O.
(a) Continue the two rays drawn leaving O to show
how they would be reflected at the mirror. [2]
GCE ‘O’ LEVEL Nov 1995
I O

40. 4.(b)I is a virtual image. Explain the meaning of
this. [2]
(Cont. …) Q. 4 Nov 1995
Since the image, I, is produced by the reflection
of light and cannot project on a screen, there-
fore it is a virtual image.