Physics Module Form 4 Chapter 5 - Light GCKL 2011 5-1 UNDERSTANDING REFLECTION OF LIGHT What light is? Is a form ……………Light travel in a .................. and high speed about 300,000 km s -1 . How the light ray reflected by the surface of mirror? 1. The light ray that strikes the surface of the mirror is called ……………….ray. 2. The light ray that bounces off from the surface of the mirror is called …………….. 3. The ……………is a line perpendicular to the mirror surface where the reflection occurs. 4. The angle between the incident ray and the normal is called the ……………… 5. The angle between the reflected ray and the normal is called ……………………………………………. AO = incident ray OB = reflected ray i = angle of incident r = angle of reflected What is the Law of Reflection ? The Laws Of Reflection 1. The incident ray, the reflected ray and the normal …………………………………..The angle of incident, i, is ………………..to the angle of reflection, r. Draw the ray diagram of the plane mirror 1. Consider an object O placed in front of a plane mirror. 2. Measure the distance between the object o and the mirror. 3. Measure the same distance behind the mirror and mark the position as the image. 4. Draw the diverging ray from a point on the image to the corner of the eye. The rays from the image to the mirror must be dotted to show that are virtual. 5. Finally, draw two diverging rays from the object to the mirror to meet the diverging rays from the image. 5.1
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Physics Module Form 4 Chapter 5 - Light GCKL 2011
5-1
U N D E R S T A N D I N G R E F L E C T I O N O F L I G H T
What light is? Is a form ……………Light travel in a .................. and high speed about 300,000 km s-1
.
How the light
ray reflected
by the surface
of mirror?
1. The light ray that strikes the surface of
the mirror is called ……………….ray.
2. The light ray that bounces off from the
surface of the mirror is called
……………..
3. The ……………is a line perpendicular
to the mirror surface where the reflection
occurs.
4. The angle between the incident ray and
the normal is called the ………………
5. The angle between the reflected ray and
the normal is called
…………………………………………….
AO = incident ray
OB = reflected ray
i = angle of incident
r = angle of reflected
What is the
Law of
Reflection ?
The Laws Of Reflection
1. The incident ray, the reflected ray and the normal …………………………………..The
angle of incident, i, is ………………..to the angle of reflection, r.
Draw the ray
diagram of the
plane mirror
1. Consider an object O placed in front of a
plane mirror.
2. Measure the distance between the object
o and the mirror.
3. Measure the same distance behind the
mirror and mark the position as the image.
4. Draw the diverging ray from a point on
the image to the corner of the eye. The rays
from the image to the mirror must be
dotted to show that are virtual.
5. Finally, draw two diverging rays from
the object to the mirror to meet the
diverging rays from the image.
5.1
Physics Module Form 4 Chapter 5 - Light GCKL 2011
5-2
State the
characteristics
of the image
formed by
plane mirror
1 .
2.
3.
4.
5.
What is meant
by virtual
image?
Image that ……………..be seen on a screen.
What is meant
by real image?
Image that ………………be seen on a screen.
CURVED MIRRORS:
Concave mirror Convex mirror
State the
differences
between
concave mirror
and convex
mirror
1.Light (diverged, converged)
2.(virtual,real) principal focus
3.PF = ……………………………
= Distance between the virtual
principal focus and the pole of the
mirror.
1.Light (diverged, converged)
2. (virtual,real) principal focus
3. PF= ………………………………
= Distance between the real principal focus
and the pole of the mirror.
Common
terminology of
reflection of
light on a
curved mirror
Refer to the diagrams above and give the names for the following:
1.Centre of curvature ,C = ……………………………………………………………………………….
plane mirror in Diagram 7.2. The curve mirror is used
to overcome the problem that occur in (a)(iii).
DIAGRAM 7.3
(i) Give the name of the curve mirror.
…………………………………[1 mark]
(ii) Complete the ray diagram in Diagram 7.3
[2 marks]
(iii) Based on your answer in b(ii), how the curve
mirror solved the problem in (a) (iii)?
…………………………………………………
[1 mark]
( C) The characteristics of the image formed by the
curved mirror in Figure 7.3 is diminished,
virtual and upright.
(i) What happen to the characteristics of the
image when the focal length of the curved mirror
is increased?
………………………………………………………..
………………………………………………..
[1 mark]
(ii) Give the reason for your answer in (c)(i).
……………………………………………………..
…………………………………………………
[1 mark]
Physics Module Form 4 Chapter 5 - Light GCKL 2010
5-9
U N D E R S T A N D I N G R E F R A C T I O N O F L I G H T
The diagram shows the spoon bent when put inside the water.
State the
phenomenon
occurs.
………………………………….
How the
phenomenon
occurs?
Light travel from ………………..medium which is air to …………………….(water), light will
be deviated ………………….to the normal. Thus the spoon seems like bending after putting
inside the water.
Why light is
refracted?
It due to change in the …………………of light as it passes from one medium into another.
Light travel more ………………in water (or glass) than in air.
When a light beam passes from air into glass, one side of the beam is slowed before the other.
This makes the beam ………………………….
Three different
cases of refraction
Case 1:
i = 0 ,r = 0
Case 2:
i > r
Case 3:
i < r
5.2
Physics Module Form 4 Chapter 5 - Light GCKL 2010
5-10
When a ray of light crosses
the boundry between two
different mediums at a right
angle or the incident ray
………………..to normal,
the ray is
…………………but
the speed of light is
…………………….
The angles of
incidence and
refraction
are………………….
Ray is light passes from
air(less dense) to
glass(denser).
ray is bent
……………………...
the normal
the speed of light
…………………after
entering the glass
Ray of light passes from
glass(dense) to air(less
dense)
ray bent
………………..from
the normal
the speed of light
…………………….
after emerging from
the glass.
State the Laws of
Refraction
The Laws Of Refraction
When the light travel from one medium to another medium which has a different optical density:
1……………………………………………………………………………………………………
2. ………………………………………………………………………………………………….
Refractive Index
1. When light travels between two mediums with different optical densities, it changes speed
and bends.
2. The speed of light will decrease when it enters an optically denser medium and increases when
it enters an optically less dense medium.
3. The angle of bending of light depends on the refractive index of the mediums and the angle of
incidence ,i.
How to define
refractive index
1. Refractive index, n is defined as,
where n = Refractive index
i = the angle in medium less
dense
r = the angle in denser medium
A material with a higher
refractive index has a higher
density.
The value of refractive index , n
1
The refractive index has no units.
Example:
The diagram shows a ray of light passing from
air to the block X.
Calculate the refractive index of the block X.
Solution:
n = sin 50°
sin 40°
= 1.2
n = sin i
sin r
Physics Module Form 4 Chapter 5 - Light GCKL 2010
5-11
2.
Example:
The speed of light in vacuum is 3 x 108 ms-1
and the speed of light in glass is 2 x 108 ms-1 .
Determine the refractive index of glass.
Solution:
n = 3 x 108 ms-1
2 x 108 ms-1
= 1.5
3.Real Depth and Apparent Depth
The following terms are defined:
Real depth,H = The distance of the real
……………… O from the surface of the water.
Apparent depth, h= The distance of the
………………..I from the surface of the water.
The refraction of light gives us a false
impression of depth.
Example:
A) The fish in the pond appears to be closer to
the surface than it actually is.
(B) The apparent depth – a swimming pool
looks shallower than it really is.
n = speed of light in vacuum (air)
speed of light in medium
0r
n = va
vm
n = Real depth , H
Apparent depth, h
Or
n = H
h
Physics Module Form 4 Chapter 5 - Light GCKL 2010
5-12
( C) A straight object place in water
looks bent at the surface.
Explanation:
1.Rays of light from the object travel from
………………………
2.Water is a ……………………..medium
compared to air.
3. Therefore, rays of light
………………….from the normal as they
leave the water. The rays of light then enter the
eyes of the observer.
4. So the object appears to be
…………………the surface of the water.
Experiment to investigate the relationship between the
angle of incidence and the angle of refraction.
Hypothesis:
The angle of refraction ………………. as the angle of
incidence ………………………
Aim of the experiment :
To investigate the relationship between
…………………………. and ……………………..
Variables in the experiment:
Manipulated variable: ……………………………..
Responding variable: ………………………………
Fixed variable: ……………………………………..
List of apparatus and materials:
Glass block, ray box, white paper protactor, power
supply .
Experiment to investigate the relationship between
real depth and apparent depth.
Hypothesis:
The apparent depth …………………..as the real depth
………………………..
.
Aim of the experiment :
To investigate the relationship between
……………….and the …………………………………..
Variables in the experiment:
Manipulated variable: …………………….
Responding variable: ……………………..
Fixed variable: ………………………………
List of apparatus and materials:
Pin, ruler, water, retort stand ,tall beaker
Physics Module Form 4 Chapter 5 - Light GCKL 2010
5-13
Arrangement of the apparatus:
The procedure of the experiment which include the
method of controlling the manipulated variable and
the method of measuring the responding variable.
The glass block is placed on a white paper.
The outline of the sides of the glass block are traced on
the white paper and labelled as ABCD.
The glass block is removed.
The normal ON is drawn.
By using a protractor , the angle of incidence, i , is
measured = 20°.
The glass block is replaced again on its outline on the
paper.
A ray of light from the ray box is directed along
incidence line.
The ray emerging from the side CD is drawn as line PQ.
The glass block is removed again.
The point O and P is joined and is drawn as line OP.
The angle of refraction, r is measured.
The experiment is repeated 5 times for the other angles of
incidence, i= 30° , 40°,50°, 60° and 70°.
Tabulate the data:
Sin i
Sin r
Analysis the data:
Plot the graph Sin r against Sin i
Arrangement of the apparatus:
The procedure of the experiment which include the
method of controlling the manipulated variable and
the method of measuring the responding variable.
A pin is placed at the base of the beaker as object O.
The another pin is clamped horizontally onto the retort
stand as image position indicator, I
The beaker is filled with water.
By using a ruler ,the real depth of the pin is measured, H=
8.0 cm
The pin O is seen vertically above the surface of the
water.
The position of pin I is adjusted until parallax error
between the pin O and the pin I is non- existent.
By using the ruler again ,the position of pin I is measured
as the apparent depth = h
The experiment is repeated 5 times for the other value of
the real depth of water, ,i.e. D=10 cm,12 cm,14 cm and
16 cm.
Tabulate the data:
H/cm
h/cm
Analysis the data:
Plot the graph h against H
Physics Module Form 4 Chapter 5 - Light GCKL 2010
5-14
Check Yourself:
Objective Question:
1 When light travels from one medium to another,
refraction take place. Refraction is caused by the
change in the
A amplitude of light rays
B intensity of light rays
C strength of light rays
D velocity of light rays
2 An observer cannot see the coin in an empty glass
as shown in Figure(a). However , he can see the
coin when the glass is filled with water as shown
in Figure(b).
Figure (a)
Figure (b)
The observer can see the coin in Figure (b) due to
A the total internal reflection of light
B the refraction of llight
C the reflection of light
D the diffraction of light
3 Which of the following is not caused by the
refraction of light ?
A A fish in pond appears nearer to the surface
of the water
B The sunlight reaches to the earth in a curve
path
C A ruler appears to bend at the water surface.
D The sea water appear in blue colour
4 Figure shows a light ray travelling from medium
R to medium S.
Which of the following is true?
A The speed of light in medium R is larger than
the speed of light in medium S
B The optical density of medium R is larger
than the optical density of medium S
C The refractive index of medium R is larger
than the refractive index of medium S
5 The diagram shows a light ray directed into a
glass block.
Which is the angle of refraction?
6 A light ray travels from medium P to medium Q.
Which of the following diagrams correctly shows
the path of the light ?
[ Medium P denser medium and Medium Q less
dense ]
Physics Module Form 4 Chapter 5 - Light GCKL 2010
5-15
7 The diagram shows a light ray travels from liquid
L to liquid M.
Which of the following diagrams correctly shows
the path of the light ?
[ Refractive index of liquid M > Refractive index
of liquid L ]
8 The diagram shows a light ray which travels from
the air to the glass.
What is the refrective index of the glass?
A Sin S B Sin P
Sin Q Sin R
C Sin Q D Sin R
Sin R Sin S
9 Which of the following formulae can be used to
determine the refractive index of a medium?
A Angle of incidence
Angle of refraction
B Apparent depth
Real depth
C Speed of light in vacuum
Speed of light in the medium
10 The diagram shows a light ray travels from the air
into medium X.
What is the refractive index of medium X?
A 0.85
B 1.24
C 1.31
D 1.41
E 1.58
11 The diagram shows a light ray travels from the oil
into the air.
What is the value of k?
[ Refractive index of oil = 1.4 ]
A 44.4o
B 45.6o
C 54.5o
D 55.4o
E 58.9o
Physics Module Form 4 Chapter 5 - Light GCKL 2010
5-16
12 The diagram shows a light of ray travels from the
air into a glass block.
What is the refractive index of the glass block?
A 1.38
B 1.45
C 1.51
D 1.62
E 1.74
13 The speed of light in the air is 3 x 108 ms-1 .
What is The speed of light in a plastic block?
[ Refractive index of plastic = 1.2 ]
A 1.0 x 108 ms-1
B 1.5 x 108 ms-1
C 2.0 x 108 ms-1
D 2.5 x 108 ms-1
E 3.0 x 108 ms-1
14 The diagram shows a boy appearing shorter when
he is in a swimming pool. The depth of the water
in the pool is 1.2 m.
[ Refractive index of water = 1.33 ]
What is the apparent depth of the pool?
A 0.1 m B 0.3 m
C 0.9 m D 1.1 m
E 1.6 m
15 The diagram shows a coin is put at the base of
the beaker. The image of the coin appears to be 5
cm from the base of the beaker.
What is the refractive index of the liquid?
A 8 B 5
13 8
C 11 D 13
5 8
E 19
14
Answer:
1 11
2 12
3 13
4 14
5 15
6 16
7 17
8 18
9 19
10 20
Physics Module Form 4 Chapter 5 - Light GCKL 2010
5-17
Section A
(Paper 2)
Structure Question:
1. The Diagram shows a side view of a water-filled
aquarium RSTU. An electric lamp, surrounded by a
shield with a narrow transparent slit, is immersed in
one corner of the aquarium at U. The light ray from
the slit shines on the water surface RS at an angle of
40o as shown in diagram below.
[2 ma
(a) What is meant by refractive index of a
substance?
[1 mark]
(b) If the refractive index of water is 1.33,
calculate the critical angle for a ray travelling
from water to air.
[ 2 marks]
(C ) (i) Draw a Diagram of the light ray shown on
diagram 3.1, meeting the water surface RS, and show
its path after meeting the surface. [1 mark]
ii. Calculate the angle that this new path makes with
RS and label the angle. [1 mark]
(d) The lamp is then placed outside underneath
the aquarium with the light striking to the bottom of
the aquarium as shown in Diagram 3.2. Draw the light
ray on Diagram 3.2, after striking the aquarium.
[1 mark]
DIAGRAM 3.1
Aquarium 40o
R S
T U
Light
ray
Water
Lamp
T
S 40o
U
R
Light ray
Water
Light ray
water
Physics Module Form 4 Chapter 5 - Light GCKL 2010
5-18
2. An observer is looking at a piece of coin at the bottom of a glass filled with water as shown in Diagram 3. He found that the image of the coin is nearer to the surface of the water.
[
2
m
a
r
k
s
]
(a)(i) State a characteristic of image in Diagram 3.
[1 mark] [ 1 1 ]
(ii) Name the science phenomenon involve in the observation above. [1 mark]