light

LESSON 1- REFRACTION OF 1.3 Refractive index,n
LIGHT
The refractive index is a determinant of the
1.1 Introduction sterength of the bending of light when light rays
travel from vacuum to a medium.
Refraction of light is a phenomenon where the
direction and speed of light are changed ( change 1.3.1. The definition of the refractive index
in velocity) when it crosses the boundry between
two materials of different optical densities. The refractive index is defined as:

1.2 Three ways in which a ray can travel Refractive index  speed of light in vacuum
through two mediums speed of light in medium

1 When a ray of light travels from optically less n c
dense medium to optically denser medium , the v
ray is bent towards the normal.
After entering the denser medium the speed of c = 3 x 108 m s-1
light decreases and angle of incidence > angle
of refraction. 1.3.2. Relationship between refractive index
and optical density of medium
2 When a ray of light travels from optically
denser medium to optically less dense medium , The optical density of a medium is not the same
the ray is bent away from the normal.
After entering the less dense medium the speed as its physical density
of light increases and angle of incidence < angle
of refraction. Optical density determines how much a light

3 When a ray of light crosses the boundry wave is slowed down as it passes through a
between two different mediums at a right angle
or the incident ray parallel to normal, the ray is medium. The more optically dense a material is,
not bent but the speed of light is different.
The speed of light decrease when ray travel the slower that a wave will move through the
from less dense medium to denser medium and
the speed of light increase when the ray of light material. The refractive index is a measurement
travel from denser medium to less dense
medium. of optical density.
The angles of incidence and refraction are zero.
The following table shows the refractive index

for some media.

Medium Refractive index, n

Vacuum and air 1.00

Ice 1.31

Water 1.33

Alcohol 1.38

Olive oil 1.46

Parafin 1.48

Perspex 1.50

Glass (crown) 1.52

Glass (flint) 1.66

Diamond 2.42

Refractive index ≥ 1 and has no unit.

From the table above , we can make a

conclusion that the higher the optical density a

medium , the higher the refractive index and the

smaller the bending.

Optical density : ρ1 < ρ2 < ρ3
Refractice index
Angle of refraction : n1 < n2 < n3
Speed of light : θ1 > θ2 > θ3

: v1 > v2 > v3

1

1.4 Law of refraction to medium 2 or vice-versa :

1.4.1 First law : Use the formula :
n1 sin θ1 = n2 sin θ2
The incident ray , normal and the
refracted ray all lie in the same plane 1.4.3 Experiment to determine the
refractive index of a glass block.
1.4.2 Second law ( Snell’s law):
Aim of the experiment :
Snell’s law states “the ratio of the sines of the
angles of incidence and sines the angles of To determine the refractive index of glass
refraction are constant” when the passes block.
between two given media.
List of apparatus and materials:
sinus i  constant  n
sinus r Glass block, ray box, white paper
protractor,power supply

Arrangement of the apparatus:

Based on the Snell’s law

sin i  n1 and sin i n2
sin 1 sin 2

Hence n1 sin θ1 = n2 sin θ2

As the conclusion :

(1) When ray of light travel from air to a The procedure of the experiment
medium or vice-versa :
The glass block is placed on a white paper.
Use the formula : The outline of the sides of the glass block
n  sin i are traced on the white paper and labelled as
sin r ABCD.
The glass block is removed.
(2) When ray of light travel from medium 1 The normal ON is drawn.
By using a protractor , the angle of incidence
is measured , i = 30o
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.

2

The ray emerging from the side CD is drawn Arrangement of the apparatus:
as line PQ.
The glass block is removed again. The procedure of the experiment which
The point O and P is joined and is drawn as include the method of controlling the
line OP. manipulated variable and the method of
The experiment is repeated 4 times for the measuring the responding variable.
other angles of incidence i = 40o, 50o, 60o
and 70o The glass block is placed on a white paper.
The outline of the sides of the glass block are
Data: traced on the white paper and labelled as
ABCD.
i (o) 30 40 50 60 70 The glass block is removed.
r (o) The normal ON is drawn.
sin i By using a protractor , the angle of incidence is
sin r measured , i = 30o
The glass block is replaced again on its outline
Calculation: on the paper.
A ray of light from the ray box is directed along
Plot the graph sin i against sin r incidence line.
The ray emerging from the side CD is drawn as
Determine the gradient of the graph = m line PQ.
Refractive index , n = m The glass block is removed again.
The point O and P is joined and is drawn as line
1.4.4 Experiment to investigate the OP.
relationship between the angle of incidence The experiment is repeated 4 times for the other
and the angle of refraction. angles of incidence i = 40o, 50o, 60o and 70o

Hypothesis: Tabulate the data:

The angle of refraction increases as the angle of i (o) 30 40 50 60 70
incidence increases. r (o)
sin i
Aim of the experiment : sin r

To investigate the relationship between the Analysis the data:
angle of incidence and the angle of refraction.
Plot the graph sin r against sin i
Variables in the experiment:

Manipulated variable: Angle of incidence
Responding variable: Angle of refraction
Constant variable: Refractive index

List of apparatus and materials:

Glass block, ray box, white paper
protractor,power supply

3

1.6 Real depth (H) and apparent depth (h) Arrangement of the apparatus:

1.6.1 : Meaning real depth and apparent The procedure of the experiment.
depth Pin 1 is placed at the base of the beaker as
object O.
Real depth, H : The depth of an object Pin 2 is clamped horizontally onto the retort
Apparent depth , h from the surface of stand as image position indicator, I
medium The beaker is filled with water.
By using a ruler ,the real depth of the pin is
: The depth of the image measured ,H = 30 cm
from the surface of The pin 1is seen vertically above the surface of
medium the water.
The position of pin 2 is adjusted until the pin
1.6.2 Relationship between n , H and h 1and the pin 2 seen colinear.
By using the ruler again ,the position of pin 2 is
Refractive index  real depth measured as the apparent depth = h
apparent depth The experiment is repeated 4 times for the other
value of H= 40 cm , 50 cm , 60 cm and 70 cm
n H Data of the experiment
h
H (cm) 30 40 50 60 70
1.6.3 Experiment to determine the refractive h (cm)
index of water. Calculation
Plot the graph H against h
. Aim of the experiment :
Determine the gradient of the graph = m
To determine the refractive index of water. Refractive index , n = m

List of apparatus and materials:

Pin,ruler,water,retort stand ,tall beaker
and metre ruler.

4

1.6.4 Experiment to investigate the Tabulate the data:
relationship between real depth and H (cm) 30 40 50 60 70
apparent depth. h (cm)

Hypothesis: Analyse the data:
Plot the graph h against H
The apparent depth increases as the real depth
increases. 1.6.5 To complete diagram of refraction of
light
Aim of the experiment :
1- Draw image of the object
To investigate the relationship between apparent 2- Draw straight line from image to the observer’s eye
depth and the real depth 3- Draw normal
4- Draw straight line from normal to objcet
Variables in the experiment: 5- Draw arrow from object to observer’s eye
Example 1
Manipulated variable: real depth Complete the following ray diagrams:
Responding variable: apparent depth (a)
Constant variable: Refractive index

List of apparatus and materials:

Pin,ruler,water,retort stand ,tall beaker

Arrangement of the apparatus:

The procedure of the experiment which (b)
include the method of controlling the
manipulated variable and the method of
measuring the responding variable.

Pin 1 is placed at the base of the beaker as
object O.
Pin 2 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 = 30 cm
The pin 1is seen vertically above the surface of
the water.
The position of pin 2 is adjusted until parallax
error between the pin 1and the pin 2 is non-
existent.
By using the ruler again ,the position of pin 2 is
measured as the apparent depth = h
The experiment is repeated 4 times for the other
value of H= 40 cm , 50 cm , 60 cm and 70 cm

5

(c) 1. 7 To solve some problem involving the
refraction of light
Solution: Example 2
(a) Diagram shows a ray of light passing from air to the
block X.
(b) [ Speed of light in air = 3 x 108 m s-1 ]

(c) Calculate
(a) The refractive index of the block X.
(b) The speed of light in the block X
Solution

Example 3
Diagram shows a ray of light passing from a glass
block to air.
[ Refractive index of glass = 1.52 ]

Determine the value of the angle θ .
Solution

6

Example 4 Example 6

Diagram shows a ray of light passing from medium Diagram shows an observer looking at a fish
M to medium N with refractive index s 1.49 and swimming in a pond.
1.36 respectively.

Calculate the angle of k. .
Solution The refractive index of the water is 1.33.
Calculate
Example 5 (a) the depth of the image of the fish?
Diagram shows a light ray NO entering in a glass (b) the distance between the observer and the image
prism.
[ Refractive index of glass = 1.51 ] of the fish.

Solution

Example 7

Diagram shows a man observing the base of a
swimming pool . The base of the pool appear to be
shallower.
The real depth of the swimming pool is 2.0 m.
[ Refractive index of water = 1.33 ]

(a) Why the ray NO does not bent when (a) What is the apperent depth of the swimming
entering the glass prism. pool?

(b) Draw the ray light after it passes through a (b) In diagram above ,draw a ray diagram
point P and determine the angle of refraction from point Z to show how the point Z appear
when the ray light entering the air again. shallower.

Solution Solution
(a)
(a)
(b)
(b)

7

TUTORIAL 1 4 Diagram shows a light ray propagating from air
into block M.
1 When light travels from one medium to another,
refraction take place. Refraction is caused by Wwhich of the physical quantity is zero?
the change in the A Speed of light
A amplitude of light rays B Angle of incidence
B intensity of light rays C Optical density of block M
C strength of light rays D Refractive index of block M
D velocity of light rays 5 Diagram shows a light ray ON propagates from
medium 1 into medium 2. The optical density of
2 Diagram shows a light ray propagating from air medium 1 smaller than the optical density of
into water. medium 2.

Which path of light ray is correct when the light
ray enter the water?

Which path A, B, C or D shows the correct
propagation of light ray O after through point
N?

6 Diagram shows a refraction of light when the
light propagates from air to perspex block.

3 Diagram shows ray of light propagate from Which path of light ray is correct when perspex
glass to air. block is replaced with a higher optically denser
block.

Which row describes how the speed and the
direction of the ray of light change when it
enters the air?

speed in air direction in air

A decreases towards to the normal
B decreases away from the normal
C increases towards to the normal
D increases away from the normal

8

7 Diagram (a) shows a ray of light propagates 11 Diagram shows a light ray travelling from
from medium F to medium G . medium X to medium Y.
Diagram (b) shows a ray of light propagates
from medium F to medium H .

Arrange the optical density of the mediums, in Which of the following is true?
ascending order. A The speed of light in medium X is larger

A G, F, H B H, F, G than the speed of light in medium Y
C F, G, H D F, H, G B The optical density of medium X is larger

8 Refractive index is defined as than the optical density of medium Y
C The refractive index of medium X is larger
A frequency of light in vacuum
frequency of light in medium than the refractive index of medium Y
D The angle of light to the normal in medium
B frequency of light in medium
frequency of light in vacuum X larger than in medium Y.
12 Diagram shows a ray of light directed to a
C speed of light in vacuum
speed of light in medium perspex block.

D speed of light in medium Which statement is correct?
speed of light in vacuum A The light refracts away from normal as it

9 Which of the following comparison is true enters the perspex block
B The incident angle is equal to the refracted
relates to a medium ?
angle
Refractive Speed Size of C The light travels slower as it enters the

index of light bending perspex block
D The brightness of light increases as it
of light
travels in the perspex block
A Small Small Small 13 Diagram shows a boy observing a stone in a

B Small Large Large pond. The stone appears to be closer to the
surface of the water.
C Large Large Small
Which reason is correct to explain this
D Large Small Large situation?

10 The refractive indices of four media W,X,Y
and Z are given by the following table

Medium WX Y Z

Refractive index ,n 1.33 1.50 1.52 2.40

When the light travel from one medium to

another , in which case the change in speed will

be minimum and maximum?

Minimum change Maximum

of speed change of speed

A X to Y Y to X

B W to Z Z to W

C W to Z X to Y

D X to Y W to Z

9

A The refractive index of air > the refractive 16 Which path A, B, C or D, shows the correct
index of water propagation of light propagates from a medium
has small refractive index to a medium has a
B The speed of light in air > the speed of large refractive index.
light in water

C The optical density of air > the optical
density of water

D The frequency of light in air > the
frequency of light in water

14 Diagram shows a light ray travels from liquid
P to liquid Q.

Which of the following diagram correctly shows 17 A light ray passes through a window.
the path of the light ? Which path does it take?
[ Refractive index of liquid P > Refractive

index of liquid Q ]

18 A light propagates from medium L into
medium M.

15 Table shows the refractive indices of parafin

and ice.

Substance Refractive index, n

Parafin 1.48

Ice 1.31

Based on the information in the table, which Which of the following is a pair of angle of

light ray, A, B, C or D, in diagram is correct? incidence and angle of refraction.

Angle of incidence Angle of refraction

Ah f

Bg e

Ce g

Df h

19 The diagram shows a light ray which travels

from the glass to the air.

10

What is the refrective index of the glass? 24 Diagram shows a beam of light travelling from
air into water.

A n  sin w B n  sin y
sin y sin w

C n  sin x D n  sin z
sin z sin x

20 Diagram shows a ray of light propagates from What is the rcfractive index of water?
medium 2 into medium 1.

A 1.14 B 1.19
C 1.33 D 1.80

25 Diagram shows a light ray travels from the
air into medium X.

Based on diagram which of the following is true
related to Snell’s law

What is the refractive index of medium X?

A n1sin c = n2 sin a A 0.85 B 1.24
B n1sin b = n2 sin d C 1.31 D 1.41
C n1sin a = n2 sin c
D n1sin d = n2 sin b 26 Diagram shows a light of ray travels from
the air into a glass block.
21 The speed of light in air is 3.0 x 108 m s-1. What
is the speed of light in olive oil of refractive
index 1.46?

A 4.8 x 1010 m s-1 B 4.5 x 109 m s-1
C 4.4 x 108 m s-1 D 2.1 x 10s m s-1

22 The speed of light in the air is 3.0 x 108 ms-1 . What is the refractive index of the glass block?
When the light move into a plastic block the
speed of light is 2.2 x 108 ms-1 .What is the
refractive index of the plastic block.

A 0.73 B 1.33 A 1.38 B 1.45
C 1.36 D 2.24
C 1.51 D 1.62

23 Diagram shows a ray of light entering a 27 Diagram shows a light ray propagating from
transparent glass block. water to air. The refractive index of water is
1.33.

What is the refractive index of the glass block?

A 0.56 B 0.64 What is the angle s?
C 1.54 D 1.78
A 22.1°
C 48.3° B 41.7°
D 60.0°

11

28 A beam of light going through a medium with 32 Diagram shows a coin is placed at the base of
a beaker. The image of the coin appears as
refractive index of 1.14 has an angle of shown in the diagram.
incidence of 42∘ with another medium. When
the light ray is at a new angle of 36∘, what is the

refractive index for the second medium?

A 0.86 B 1.00
C 1.17 D 1.30

29 Diagram shows a ray of light is incident through
a diamomd with refractive index 2.42, on an
interface separating diamond and parafin with
refractive index 1.48.

What is the refractive index of the liquid?

A9 B 13
4 9

C 20 D 16
16 13

33 Diagram shows an observer looking the iamge
of a fish swimming in a pond.

What is the angle of refraction , g , the angle of
incidence of the ray in diamond is 30 °?

A 54.8o B 52.3o
C 37.7o D 35.2o

30 Diagram shows a pencil in a beaker filled with
water.

.

What is the distance bwtween the fish and the
observer’s eye.

[The refractive index of the water is 4 ]
3

A 50.0 cm B 41.3 cm
C 20.0 cm D 11.3 cm

34 Diagram 34 shows a decorative lamp has a
transparent liquid in the space above a bulb.
Light from the bulb passes through rotating
coloured filters giving the different colours in
the liquid.

At which point, A, B, C or D, is the image
position of the pencil?

31 A man sees a fish in a lake.Which labelled path
is taken by the light travelling from the fish to
the man’s eye?

12

Based on Diagram 35,

(a) Complete the ray diagram until the ray of
light emerges in air again.
[ 2 marks ]

(b) Calculte all angles between normals and the
boundaries of medium.

Diagram 34 [ 3 marks ]
(a) Name the light phenomenon involved at the 36 Diagram 36.1 and Diagram 36.2 show a ray of

liqiud-air boundary. light with angle of incidence 70o propagates
........................................................................ from air to block R and to block S respectively.

[ 1 marks] Diagram 36.1
(b) Explain how the phenomenon occured.

........................................................................
........................................................................
........................................................................
........................................................................

[ 2 marks ]
(b) Calculate the refractive index of the liquid.

[ 2 marks ] Diagram 36.2
(c) The speed of light in air is 3 x108 m s-1. (a) Based on Diagram 36.1 and Diagram 36.2

Calculte the speed of the blue light in compare
the liquid. (i) the refractive index of the blocks.

[ 2 marks ] ..................................................................
35 Diagram 35 shows a ray of light passes from air [ 1 mark ]

to crown glass and then into water . (ii) the speed of light , v in the blocks.
..................................................................
[ 1 mark ]

(iii)the angle of refraction in the blocks
..................................................................
[ 1 mark ]

(b) Based on your answer in (a), states the
relationship between
(i) the refractive index and the speed of light
in medium.
..................................................................
[ 1 mark ]
(ii) the speed of light and the angle of
refraction in medium.
..................................................................
[ 1 mark ]

Diagram 35

13

(c) Diagram 36.3 shows a spoon is immersed in 38 (a) Diagram 38.1 and Diagram 38.2 show
a beaker of water. the positions of the image seen by the
observer when two identical coins are
placed in beaker containing with
different depth of water.

Diagram 36.3 Diagram 38.1
On Diagram 36.3, complete the ray diagram
to show how the image of the spoon is seen.

[ 2 marks ]
37 Diagram 37 shows a man throws a spear

toward a fish but the spear fails to hit the fish.
.

Diagram 37 Diagram 38.2

(a) Name the phenomenon of light involved (i) What is meant by by apparent depth.
shown in Diagram 37. [ 1 mark]
…………………………………….…..........
[ 1 mark ] (ii) Observe Diagram 38.1 and Diagram
38.2, compare the real depth and the
(b) Underline the correct answer in the bracket apparent depth of the coin and the
to complete the sentence below. refractive index of the water.
Phenomenon in (a) happens because of State the relationship between real depth
the change in (velocity, frequency) of the and the apparent depth. Name the light
light. phenomenon involved.
[ 1 mark ] [ 5 marks]

(c) Give one reason why the spear fails to hit (b) Why do Stars twinkle? Explain your answer.
the fish. [ 4 marks ]
..................................................................
[ 1 mark] (c) Diagram 38.3 shows a ray of light AO
moves in a liquid which has refractive index
(d) Give one suggestion how to hit the 1.22 and then passes through a plastic
fish accurately. prism. OB is the path of the light ray in the
.................................................................. plastic prism.
[ 1 mark]

14

Diagram 38.3 Based on your observations on the level of the
water and the position of the images of the fish:
(i) Calculate the refractive index of the plastic (a) State one suitable inference.
prism.
[ 2 marks] [ 1 mark]
(b) State one suitable hypothesis.
(ii) Draw the ray of light started from B to show
the path of ray in the liquid again. [ 1 mark]
Calculate the angle of refraction at B. (c) With the use of apparatus such as a tall

[ 3 marks] beaker, pins and other apparatus, describe an
39 Diagram 39.1 and Diagram 39.2 shows two experiment to investigate the hypothesis
stated in (b).
identical aquariums but with different level of In your description, state clearly the
water. following:
When a fish in the aquarium is observed from (i) The aim of the experiment.
the same position, the position of the images (ii) The variables in the experiment..
of the fish are shown in the diagrams. (iii) The list of apparatus and materials.
(iv) The arrangement of the apparatus.
(v) The procedure used in the

experiment.Describe how to control and
measure the manipulated variables and
how to measure the responding
variables.
(vi) The way to tabulate the data.
(vii)The way to analyse the data.

[10 marks]

Diagram 39.1

Diagram 39.2

15

LESSON 2 - TOTAL INTERNAL Arrangement of the apparatus:
REFLECTION
The procedure of the experiment
2.1. How the total internal reflection occur? Place a semi-circular glass block on white
2.1.1. Introduction. paper.
As we already know , when the ray of light Draw the border of the semi-circular glass block
propagates from large optical density medium to on white paper and mark as PQR.
the small density medium , refraction away Remove the glass block and mark the center of
from the normal occured. the glass block as O
Draw normal ON.
But what happens when the angle of incidence Place again the glass block back on the white
is gradually increased. The angle of refraction paper.
become larger until the ray of light back into the Turn on the ray of light and point the ray to
large optical density medium. center O at an angle of incidence, i.
Repeat the experiment by adding the angle, i.
At this moment , the total internal reflection Observed what happens.
occured. The boundary of two mediums act as a By using a protractor , measure the angle of
reflector. incidence when the angle of refraction is 90o,
2.1.2 Experiment to show how the total =c
internal reflection and to determine the
critical angle of the semi-circular glass block. Observation
Aim of the experiment : When the angle incidence is small , the
To show how the total internal reflection and to refraction and the reflection occur.
determine the critical angle of the semi-circular When the angle of incidence , i greater the angle
glass block. c , all ray of are reflected.
List of apparatus and materials:
Semi-circular glass block, ray box, white paper 2.1.3 Ray diagram to show how the Total
protractor and power supply Internal Reflection happen ?

16 (1) Angle of incidence ,i1 is small.
Produces a strong refracted ray and a weak
reflected ray.
(2) Angle of incidence is increased as i2.
Produces a refracted ray and a reflected ray
whose intensity has increased compared to the
situation in (1)
(3) Angle of incidence is increased to the

critical angle, c.
The refracted ray travels along the water-air
boundary.
(4) Angle of incidence , i3 > c.
No refraction occurs.
All the light is reflected within the water .
Total internal reflection occurs

2.1.4 The conditions for the occurrence of 2.2.2 Determine the relationship between
total internal reflection. Refractive index (n) and Critical angle (c)
(1) The light ray must be travel from an
n  sin i
optically denser medium to less dense sin r
medium.
(2) The angle of incidence must be greater than  sin 90o
the critical angle. sin c
2.2 The Critical Angle, c
2.2.1 The meaning of the critical angle 1
The angle of incidence when the angle of sin c
refraction is 90o.
Example 1 As conclusion :
Mark in the following diagrams the critical n 1
angle with ”c” . sin c

Solution Example 2
The critcal angle of diamond is 24.4o.
Determine the refractive index of diamond.
Solution

Example 3
The refractive index a glass is 1.51. Calculate
the critical angle of the glass.
Solution
n 1

sin c
c  sin 1 1   41.47o

 1.51 
2.2.3 Experiment to investigate the
relationship between the refractive index, n
and the critical angle,c
Hypothesis:
As the refractive index increases , the critical
angle decreases.
Aim of the experiment :
To investigate the relationship between the
refractive index, n and the critical angle,c
Variables in the experiment:

17

Manipulated variable: Refractive index 2.2.4 Experiment to show how the total
Responding variable: Critical angle internal reflection in liquid occured
Constant variable: Diameter of semi-circular
block and colour of light Aim of the experiment

List of apparatus and materials: To show how the total internal reflection in
Semi-circular block with different materials, liquid occured.
laser pen , white paper and protractor
List of apparatus and materials
Arrangement of the apparatus:
Laser pen , binder clip , books , plastic drinking
The procedure of the experiment which bottle , cellophane tape, plastic basin , water
include the method of controlling the and cooking oil
manipulated variable and the method of
measuring the responding variable. Arrangement of the apparatus:

Place a semi-circular ice block of refractive The procedure of the experiment
index . n = 1.31on white paper.
Draw the border of the semi-circular ice block Drill a hole near the bottom of the wall of bottle
on white paper and mark as PQR. with a pin has a diameter which is slightly
Remove the semi-circular ice block and mark larger than the diameter of the laser that will be
the center of the block as O used.
Draw normal ON. Tape the hole and then fill the bottle with water.
Place again the semi-circular ice block on the Stand the soda bottle on top of a stack of books
white paper. so the hole is facing the plastic basin.
Turn on the laser pen and point the ray to center Carefully remove the tape and then unscrew the
O. top of the soda bottle and turn on the laser pen.
Increase the angle of incidence until the ray of Obeserve the path of light in the stream of
laser light on OQ. water.
By using a protractor , measure the angle of Repeat the experiment by using cooking oil.
incidence = c
Experiment is repeated 4 times by using Observation
different type of semi-circular block such as
Pyrex (n =1.47) , Perspex (n =1.49) , Crown The total internal reflection occur many times in
glass ( n = 1.52) and Flint glass ( n= 1.61) the stream of liquids until out from the end of
the liquids stream.
Tabulate the data: The number of total internal reflection in
Refractive 1.31 1.47 1.49 1.52 1.61 cooking oil larger than in the water.
index, n
Critical
angle (o)
Analysis the data:

Plot the graph c against n

18

Discussion 2.3.3 Sparkling of diamond
The number of total internal reflection in
cooking oil larger than in the water because the The optical density of diamond is high
cooking oil has the refractive index larger than and caused the the refractive index is
water. So that the critical angle of the cooking large.
oil smaller than the water caused the total As the result the critical angle of
internal relection easy to occur. diamond is small ≈24.4o
2.3 Natural phenomena and Use of Total When the light ray enters the diamond ,it
Internal Reflection. experiences multiple total internal
2.3.1 Formation of mirages reflections inside the diamond.
After many such reflections, the colors
During hot day , the incidence ray from the sun in the light are separated, and seen
passes through a high optical density air to individually.
small optical density air. 2.3.4 Prism periscope
The ray of passes through the air layer close to
hot surface at an angle of incidence greater than The periscope is built using two glass
the critical angle of cool air. prisms with its angle is 45o-90o- 45o
Total internal reflection occurs at this layer. The critical angle of the glass is 42o .
The observer sees the image of the sky on the The angle of incidence is 45o is greater than
surface of hot layer as a pool of water. the critical angle.
2.3.2 Formation of rainbow Total internal reflection occurs.
The characteristics of the images are
When the white light from the sun enters the (i) Virtual
raindrop, it experiences refraction and (ii) Upright
dispersion in seven different colors due to (iii) Same size as the object.
different wavelengths(speed). Advantages of the prism periscope
All diffrent of colors of light experience total compared to mirror periscope,
internal reflection at the surface of the raindrop, (i) The image is brighter
After reflection they experince dispersion again (ii) No multiple images is formed (very
and the observer can see the rainbow.
clear)
19

Example 4 2.3.5 Binocular
Diagram shows a structure of a periscope.

Complete the ray diagram to shows how the A ray light experiences two times of the
image the object formed? total internal reflections at each prism which
have the angles are 45o-90o- 45o .The two
Solution prisms are to invert the image (upside down
and right-to-left.) But the lenses in the
binoculars also invert the image and so the
prisms put it back the right way again.
So the final image in binoculars is upright
,not laterally inverted and magnified.

Example 5

Diagram shows the arrangement of prisms
in a binocular.

Complete ray diagram in the prisms.
Solution

20

2.3.6 Optical fiber

Bundle of optical fibers The reflector is made up of many small
persepex prisms arranged so that light
An optical fiber is a flexible ,tranparent fiber undergoes total internal reflection twice.
made by glass or plastic to a diameter The overall result is that the light is returned
slightly thicker than that of a humam hair. in the direction from which it origanally
The optical fibers are assambled in a bundle came.
to split or to combine signals. 2. 4 To solve some problem involving the total
The external outer cladding has the a small internal reflection
optical density compare to the inner core. Example 6
When light rays travel from the inner core Diagram shows a light ray AO travelling from
to the outer cladding at an angle that exceeds medium X to the air.
the critical angle, total internal reflection [The refractive index of medium X = 2.0 ]
occurs until the ray out at the end of the
optical fibre. (a) Calculate the crtical angle of the meduim X.
The advantages of the fibre optics: (b) Draw the ray light after it passes through the
(i) Cheap
(ii) Easily handled point O when
(iii)More information can be transmitted and (i) θ = 25o (ii)θ = 30o (iii) θ = 35o
Solution
received. (a)

2.3.7 Reflector on the road and bicycle
reflector

Reflector on the road (Cat’s eye)

(b) (i)

Bicycle reflector

21

(ii) Example 8
Diagram shows a light ray entering in a glass prism.
[ Refractive index of glass = 1.51 ]

(iii)

Example 7 (a) Determine the critical angle of the glass.
(b) Draw the ray light after it passes through a point
Diagram shows a rectangular glass block PQRS. A
ray of light MO is directed to the side PS and then P until the direction of the ray of light
into the glass block and reach to the side PQ at unchanged.
point N. The refractive index of the glass is 1.51.
Solution

(a)

(b)

(a) Calculate the critical angle of the glass
block.

(b) By determining the certain angles on the
glass blocks complete the light path starting
from N.

Solution
(a)

(b)

22

TUTORIAL 2 4 Which of the following diagram correctly shows
the total internal reflection of ray of light?
1 A ray of red light travelling in glass strikes the [ The refractive index of medium X > Y)
glass-air boundary . Some light is reflected and
some is refracted. Which diagram shows the
paths of the rays?

5 The critical angle of a type of coloured liquid is
47°.Which diagram shows the total internal
reflection?

2 Which of the following diagram shows the
phenomenon of total internal reflection?

6 The figure shows a ray of light PO traveling in

a liquid strikes the liquid-air boundary.
[ The critical angle of the liquid = 45o ]

In which direction does the light move from O ?

A OQ B OR
C OS D OT

3 Which of the following diagram shows the 7 Diagram shows a ray of light in a semi-circular
path of a beam of light that is incident on a glass block.
water-air surface with angle of incidence greater If the critical angle of the glass is 42o, what is
than the critical angle. the correct path for the light?

23

8 A ray of light incident on one side of a 11 Which diagram shows a ray hitting asemi-
circular glass block at the critical angle, θ?
rectangular plastic block. When the angle of
refraction in the plastic block is 42o ,which one

of the following diagrams best represents this

ray?
[ The critical angle of glass is 44o ]

12 Diagram shows the path of light from P to O.

The critical angle of water is 48°. When
θ° = 48°, which is the correct path of light after

passing through point O?

A OR B OS
C OT D OU

9 Diagram shows a ray of light starting from M 13 Diagram shows a light ray X is directed into the
entering a vertically angled glass prism and has glass block. The critical angle of the glass is
an angle of 42o. 42 0o. Which direction does the ray X propagate
After passing through the point O,Which of the from point Y?
trajectories of A, B, C or D is the actual
trajectory of the beam of light?

10 A ray of light incident on one side of a glass 14 Which of the path of ray formed the critical
prism of angle 45o – 90o – 45o at a right angle angle of water?

to the side.

Which one of the following diagrams best

represents this ray?
[ The critical angle of glass is 42.2o ]

24

15 Diagram (a) and Diagram (b) show light rays What is the critical angle of the prism X?
travelling from perspex to air at different
incident angles. A 40o B 50o
C 60o D 70o

19 The refractive index of parafin is 1.48
What is the critical angle of the parafin.

Diagram(a) Diagram(b) A 28.7o B 34.9o
C 42.5o D 47.5o

Which angle is the critical angle of the glass? 20 Diagram shows a ray of light propagates in a
transparent semi -circular block.

Ap Bq
Cr D s

16 Which of the following shows the correct
critical angle , c of the semi- circular glass
block

What is the possible value of refractive index of
the transparent block?

A 1.55 B 1.63
C 1.73 D 1.81

21 Diagram shows a ray of light passing through a
prism with refractive index of 2.00

17 Diagram shows a light ray travelling from air
into a plastic block with an angle of incidence
,X. What is the critical angle of the plastic?

Which of the following diagram correctly shows
the trajectory of an incident ray through a prism?

18 Diagram shows a light ray travelling from air
into a prism X.

22 Diagram shows a ray of light AO traveling in
strikes the medium X-air boundary.
[ The refractive index of medium X = 1.12 ]

25

25 Diagram shows a ray of light passing through
medium M to medium N.

In which direction does the light move from O ? Which of the following is correct?

A OE B OD A The angle of reflection is 55o
C OC D OB B The critical angle of medium M less than

23 The diagram shows a semi-circular plastic 35o
block is placed in a liquid. C The optical density of medium M less than

the optical density of medium N
D The refractive index of medium M less

than the refractive index of medium N

26 Which of the following shows total internal
reflection?

Which of the following is correct? 27 Which instrument uses the concept of total
internal reflection?
A The optical density of the plastic block is
less than the optical density of the liquid A Microscope
B Magfying glass
B The refractive index of the plastic block is C Prism periscope
less than the refractive index of the liquid D Astronomical telescope

C The the critical angle of the plastic block is 28 Which of the following diagram not involving
less than the critical of the liquid total internal reflection?

D The angle of incidence in plastic block is
less than the critical angle of the liquid

24 Diagram shows a ray of light is incident in air
to the surface of Prism A and B.

Which comparison is correct ?

Prism A Prism B

A Small optical Large optical

density density

B Small critical Large critical

angle angle

C Small refractive Large refractive

index index

D Small angle of Large angle of

incidence incidence

26

29 Which of the following not applies the principle (a) Calculate the magnitude angle of
of total internal reflection? (i) m

A Reflector on the road [2 marks]
B Mirror periscope
C Prism binocular (ii) n
D Road mirage
30 Diagram shows a binocular containing prisms. [1 mark]

Which arrangement of prisms is correct so that (b) Calculate the critical angle of the perspex
an observer can see the image of the object? block.

31 Rainbow is seen on sky after rain [2 marks]
Which phenomena cause the appearance of (c) On Diagram 32, starting from P complete
rainbow?
the ray diagram until the ray emerges in air
A Refraction again.
B Refraction and total internal reflection
C Total internal reflection and dispersion [2 marks]
D Rrefraction , total internal reflection and
33 Diagram 33.1 and Diagram 33.2 show material
dispersion X with a refractive index ,n of 1.32 cut into
rectangular block and semi-circular block
32 Diagram 32 shows light beam strikes the edge respectively.
of a rectangular block of Perspex WXYZ of Diagram 33.3 and Diagram 33.4 show material
refractive index 1.51 Ywith a refractive index , n of 1.46 cut into
rectangular block and semi-circular block
respectively.
The ray of light from air is directed to the
blocks.
O is the centre of the semi-circular blocks.

Diagram 33.1 Diagram 33.2

Diagram 33.3 Diagram 33.4

(a) Based on information in Diagram 33.1 ,
Diagram 33.2,Diagram 33.3 and Diagram
33.4 :

Diagram 32 (i) Draw two straight lines from the symbol
of angles to the suitable name of
angles.

27

Symbol of angle Nane of angle ........................................................................
[ 1 mark ]
incidence angle
i (b) On Diagram 34.3,
(i) draw the correct position of the prisms in
refraction angle the box P and Q.
c [ 1 mark ]
(ii) complete the path of the light ray from
critical angle the object to the observer.
[ 1 mark ] [ 2 marks ]

(ii) Compare the refractive index of the (c) You are required to modify nthe binocular
materials. that can produce sharper and clearer image
.................................................................. as well as more portable during the
[ 1 mark ] whales.
State and explain the modificattions based
(b) Based on Diagram 33.1 and Diagram 33.3 , on the following aspect
compare
(i) the size of bending of the light in the (i) Focal length of the objective lens
materials. ..................................................................
.................................................................. Reason:
[ 1 mark ] ..................................................................
(ii) the optical density of the materials. [2 marks ]
..................................................................
[ 1 mark ] (ii) Diameter of the lens:
..................................................................
(c) Based on Diagram 33.2 and Diagram 33.4, Reason:
compare the angle of ‘c ‘of the materials. ...............................................................
........................................................................ [2 marks ]
[ 1 mark ]
(iii) The characteristics of material used for
(d) Based on your answers in (a), (b) and (c) , the body of the binocular:
state the relationship between ..................................................................
(i) the refrcative index and the optical Reason:
density ..................................................................
.................................................................. [2 marks ]
[ 1 mark ]
(ii) the optical density and the angle of ‘c’. (d) The binocular and a periscope work
........................................................................ based on the phenomenon of total
[ 1 mark ] internal reflectionb but what’s different?
........................................................................
(e) Explain why the semicircular blocks are
used. [ 1 mark ]
....................................................................... 35 Diagram 35.1 shows a reflector on a road
........................................................................
[ 2 marks ] known as cat’s eye fixed into a road to help
drivers when it is dark or foggy .
34 Diagram 34.1 shows a man watches whales Diagram 35.2 shows the structure of the cat’s
in an ocean by using a binocular. Diagram eye containing perspex prism.
34 2 shows the strucutre of one side ofthe
binocular.

Diagram 35.1

Diagram 34.1 Diagram 34.2 Diagram 35.2
(a) On Diagram 35.2 ,
(a) State one characteristic of the image
produced by the binocular. (i) Mark the right angle in the prism.
[ 1 mark ]

28

(ii) Complete the path of the light ray from (c) Diagram 36.3 shows a light signal travelling
car headlamp to the driver. through an optical fiber made of glass.
[ 2 marks ]
Diagram 36.3
(b) Why the light ray does not bend when it The optical fibre in Diagram 36.3.can be
enters the prism. used in telecommunications and medicine.
………………………………………............ Give your suggestions to make the optical fiber
……………………………………................ more efficient based on the following aspects:
[ 1 mark ] -Comparison between refractive index of the

(c)(i) Name the phenomenon involved. inner core, and the outer cladding
………………………………………...... -The flexibility
[ 1 mark ] - Material of the jacket
- Purity of inner core
(ii) Why the phonomenon in (c)(i) occurred? - Assemble in single fiber or in bundle fibre
..................................................................
.................................................................. [ 10 marks ]
[ 2 marks ] 37 (a) Diagram 37.1 shows a fish is behind a large

(d) The refrcative index of perspex is 1.50. rock in a pond while a shrimp were on the
Calculate the critical angle of the perspex. other side of the stone.

[ 2 marks ]
36 (a) Diagram 36.1 shows prism M and prism N

has the critical angle 42o and 47o
respectively.

Diagram 36.1 Diagram 37.1
(i) What is meant by critical angle? (i) State one phenomenon of light involved

[ 1 mark ] [1 mark]
(ii) Based on Diagram 36.1 , compare the (ii) Explain how the fish can see the shrimp

angle of incidence at P , comparison the without going to the other side of the
magnitude the angle of incidence with stone.
critical angle and the light phenomenon
occur after point P. [4 marks]
Relate the angles involved with the light (b) Diagram 37.2 shows an observer use a
phenomenon occur.
periscope to see a distant object behind a
[ 5 marks ] high wall.
(b) Diagram 36.2 shows an observer looking

image of a sailboat at sea during night time.
The image of the sailboat appears in inverted
position in the sky.

Diagram 37.2

Diagram 36.2
Explain that observation

[4 marks]

29

Table 39 shows the design and the 38 Diagram 38.1 and Diagram 38.2 show two
specifications of four periscope P, Q, R and identical adjustable sources of light are directed
S used glass prisms and lenses.Study the two surfaces of liquid with different optical
specifications of all four periscope. Explain densities respectively. The sources of light are
the suitability of each design and its adjusted until the rays of light emerge exactly
specifications. Determine the most suitable parallel to the surface of the water.
periscope to be used by the observer. Give
reasons for your choice. Diagram 38.1

[ Critical angle of glass = 41.8o ]

Periscope P Q R S

Angles of 45o , 30o , 45o , 30o ,
prism 90o , 60o , 90o , 60o ,
45o 90o 45o 90o
Arrangem
ent of Type I Type II Type II Type I
prisms

Type of Con Con Convex Convex Diagram 38.2
lenses cave cave Based on your observations on the level of the

Shape Type I Type II Type I Type II water and the position of the images of the fish:
of outer (a) State one suitable inference.
casing
[ 1 mark]
Table 37 (b) State one suitable hypothesis.

[10 marks] [ 1 mark]
(c) With the use of apparatus such as
(c) Diagram 37.3 shows a ray of light AO is
incident to a glass prism UVW without laser pointer, protractor , white paper
change its direction until reach at B. and other apparatus, describe an
[The refractive index of glass = 1.5] experiment to investigate the hypothesis
stated in (b).
In your description, state clearly the
following:
(i) The aim of the experiment.
(ii) The variables in the experiment..
(iii) The list of apparatus and materials.
(iv) The arrangement of the apparatus.
(v) The procedure used in the

experiment.Describe how to control and
measure the manipulated variables and
how to measure the responding
variables.
(vi) The way to tabulate the data.
(vii)The way to analyse the data.

[10 marks]

Diagram 37.3

Calculate the critical angle of the glass and
hence draw the complete path of a ray started
from B until the direction of the path of ray
unchanged.

[5 marks]

30

LESSON 3 – FORMATION OF Arrangement of the apparatus:
IMAGE BY LENSES
The procedure of the experiment
3.1.Introduction Place a convex lens in front of the ray box fitted
with a multi-slit plate, onto a sheet of a white
A lens is a transparent material which consists of at paper.
least one curved surface. Trace around the lens with a pencil.
For example , the surface of water waves can acts Switch on the bulb in the ray box on and use a
as convex lens(crest) and concave lens (trough) , pencil to to show the path of the rays of light
the glass stem of thermometer in curved-shaped before and after passing through the lens.
acts as convex lens and adrinking transparent bottle Experiment is repeated by using a concave lens.
filled with liquid acts as a convex lens. Observation
Images formed by lenses due to the phenomenon of
refraction of light.
Rays of light from objects at infinity ( distant
objects) are parallel rays.
There are two types of lens i.e.convex lens and
concave lens.

3.2 To identify a convex lens as a converging lens Discussion
and concave lens as a diverging lens.
For the convex lens the parallel of light is
3.2.1 Experiment to show a convex lens as a converged to a point behind the lens. The point
converging lens and concave lens as a known as the focal point and the point is real.
diverging lens. The focal length of the convex lens is positive.

Aim of the experiment For the concave lens the parallel of light is
diverged from a point in frontof the lens. The
To show how a convex lens as a converging point known as the focal point and the point is
lens and concave lens as a diverging lens. virtual.The focal length of the convex lens is
negative.
List of apparatus and materials

Ray box, convex lens, concave lens,plate with
parallel slits , power supply, white paper and
pencil.

31

3.2.2 Common terminology of lenses 3.2.3Experiment to estimate the focal length
of a convex lens.

Aim of the experiment

To estimate the focal length of a convex lens by
observing the real image of a distant object.
.
List of apparatus and materials

Convex lens, lens holder , white screen and
ruler.

Arrangement of the apparatus:

Optical centre , O The procedure of the experiment

A point which all rays traveling through this A convex lens is turned to face a distant object
point pass through the lens in a straight line. located outside the laboratory
The position of the screen is adjusted until a
Principal axis , AB sharp inverted image is formed on the screen.
The distance of the screen from the optical
A straight line passing through the optical centre of the lens is measured by using ruler =
centre of a lens and joining the two centres x1
of curvature of its surfaces and at a right angle The experiment is repeated 4 times by facing
to the plane of the lens. the lens with differnt distant objects.
Record the distance from screen and optical
Focal point ,F centre of the lens as x2 , x3 , x4 and x5 ,

For convex lens : A point behind the lens and Calculation
on the principal axis in which the parallel rays
of parallel to the principal axis are converged The focal length , f of the convex lens is
after passing through the convex lens. calculated ,

For concave lens : A point in front the lens and f  x1  x2  x3  x4  x5
on the principal axis in which the parallel rays 5
of parallel to the principal axis are started to
diverged before passing through the concave Discussion
lens.
This experiment cannot be used to determine
Focal length , f the focal length of a concave lens ,because the
image of concave lens always virtual (Cannot
The distance between the optical centre ,) and form on the screen)
the focal point,F.

Object distance , u

Distance of the object from the optical centre,O

Image distance , v

Distance of the image from the optical centre,O

32

3.2.4 Relationship between the thickness and The procedure of the experiment which
the focal length of the lens include the method of controlling the
manipulated variable and the method of
Based on diagram above , the conclusion is measuring the responding variable.
the thicker the lens ,the shorter the focal length.
3.2.5Experiment to investigate the Measure the thickness of the centre of lens by
relationship between the thickness lens and using metre ruler ,D = 3cm
the focal length for a convex lens. The lens is faced to an object at infinity
Hypothesis: outside the laboratory
As the thickness of lens increases , the focal The screen is adjusted until a sharp image
length decreases formed.
Aim of the experiment : Measure the distance between the screen and
To investigate the relationship between the the lens = f
thickness and the focal length for a convex The experiment is repeated 4 times for D = 5 cm
lens. , 8 cm, 11 cm and 14 cm.
Variables of the experiment:
Manipulated variable: thickness of lens Tabulate the data:
Responding variable: focal length
Constant variable: diameter of lens, refractive Tabulate the data
index of lens D (cm ) 3 5 8 11 14
List of apparatus and materials: f (cm)
Screen ,convex lens,lens holder and metre ruler
Arrangement of the apparatus: Analysis the data:

Plot the graph f against D

3.3 Characteristics of image formed by lenses by
using ray diagrams.

3.3.1 Ray diagram of lenses

The main ray of light in drawing a ray diagram
are:

Ray I

33

Ray 2 Example 1

Complete the following ray diagram and state the
characteristics of image formed

Solution

Ray 3

Example 2

Complete the following ray diagram and state the
characteristics of image formed

The method to complete ray diagram for Solution
convex lens and concave lens are:

1.Draw Ray 1 from the top of object.
2.Draw Ray 2 or Ray 3 from the top of the
object.
3.Extrapolate Ray1 and Ray 2 or Ray 3
until intersect each other.
4.Draw image at the intersection point.
5.Draw arrow from object to the image

34

Example 3 (d) u =2f

(a) Complete the following ray diagrams for
convex lens
(b) State the characteristics of image formed
(c)Complete the table below

(a) u < f

(e) u > 2f

(b) u = f

(f) u = 

(c) u < f < 2f

The distance Characteristics of image
object, u
u <f
u =f
f <u < 2f
u = 2f
u > 2f
u=

35

Solution (d) u =2f
(a) u < f

Characteristics of image: Characteristics of image:
............................................................................. .............................................................................
............................................................................. .............................................................................
(b) u = f
(e) u > 2f

Characteristics of image: Characteristics of image:
............................................................................. .............................................................................
............................................................................. .............................................................................

(c) u < f < 2f (f) u = 

Characteristics of image:
.............................................................................
.............................................................................

Characteristics of image: The distance Characteristics of image
............................................................................. object, u
............................................................................. u <f
u =f
f < u < 2f
u = 2f
u > 2f
u=

36

Example 4 (b) u < f < 2f

(a) Complete the following ray diagrams for
concave lens
(b) State the characteristics of image formed
(c)Complete the table below

(a) u < f

(b) u < f < 2f Characteristics of image:
.............................................................................
...........................................................................
Object distance ,u Characteristics of image
u<f
f < u < 2f

3.4 Linear magnification ,m

3.4.1 The meaning of linear magnification ,m

The linear magnification , m of image for by a
lens is given by ;

Linear magnificat ion  height of image
height of object

Solution m  hi
(a) u < f ho

Characteristics of image: Also
.............................................................................
............................................................................. The linear magnification , m of image for by a
lens is given by ;
37
Linear magnificat ion  Image distance
Object distance

mv
u

Linear Size of image
magnification,
Image and object are
m the same size
ImI =1 Enlarged(magnified)
image
ImI >1 Diminished image

ImI <1

3.4.2 Experiment to determine the linear Aim of the experiment :
magnification of image for an object formed
by a lens. To investigate the relationship between the
object distance ,u and the linear
Aim of the experiment magnification , m.

To determine the linear magnification of image Variables in the experiment:
for an object formed by a lens
Manipulated variable: object distance, u
List of apparatus and materials Responding variable: linear magnification ,
m.
Convex lens, lens holder , white screen and Constant variable: focal length of the lens, f
ruler, cardboard with a cross-wire in a triangular
cut-out(object) List of apparatus and materials:

Arrangement of the apparatus: Convex lens, lens holder , white screen and
ruler, cardboard with a cross-wire in a
triangular cut-out(object),

Arrangement of the apparatus:

The procedure of the experiment

The distance between the object and the The procedure of the experiment which
convex lens is measured by using a ruler , include the method of controlling the
u1 = 20 cm manipulated variable and the method of
The bulb is lighted up measuring the responding variable.
The screen is moved back and forth until a
sharp image is formed on it. The distance between the object and the
The distance between the screen and the lens convex lens is measured by using a ruler ,
is measured , v1. u = 20 cm
The experiment is repeated 4 times for the The bulb is lighted up
other object distances u2 = 30 cm, u3 = 40 The screen is moved back and forth until a
cm, u4 =50 cm and u5=60 cm sharp image is formed on it.
The distance between the screen and the lens
Calculation is measured , v.
The linear magnification is calculated ,
The linear magnification is calculated ,
v
m1  v1 m
u1
u
Calculate the linear magnification , m2 , m3 , The experiment is repeated 4 times for the
,m4 and , m5. other object distances ,u= 30 cm , 40 cm., 50
Calculate the average linear magnification , cm and 60 cm.
Tabulate the data:
m
u(cm) 20 30 40 50 60
m  m1  m2  m3  m4 5 m
5
Analysis the data:
3.4.3 Experiment to investigate the Plot the graph m against u

relationship between the object distance

,u and the linear magnification , m.

Hypothesis:

As the object distance ,u increases ,the
linear magnification decreases.

38

3.5 Thin lens equation The procedure of the experiment

3.5.1 Thin lens equation The distance between the object and the
convex lens is measured by using a ruler ,
Thin lens equation is given by: u = 20 cm
11 1 The bulb is lighted up
fu v The screen is moved back and forth until a
sharp image is formed on it.
Where ; f = focal length The distance between the screen and the lens
u = object distance is measured , v.
v = image distance The experiment is repeated 4 times for the
other object distances ,u= 30 cm , 40 cm., 50
3.5.2 Sign Conventions for lens equation cm and 60 cm.

Convex lens Concave lens Plot the graph 1 against 1
uv
Object + if object in + if object in
Determine the 1 - intercept and 1 -
distance front of lens and front of lens and uv

,u – if object – if object intercept

behind the lens behind the lens

Image + if image + if image

distance , behind of lens behind of lens

v (real image) and (real image) and Calculation

– if image in – if image in 1 - intercept = a
u
front the front the

lens(virtual lens(virtual 1 - intercept = b
v
image) image)

Focal + - 1 1
a b
length, f f1  and f2 

3.5.3 Graph of lenses based on the thin lens

equation Calculate the average focal length

f  f1  f2
2

3.4.5 Experiment to investigate the

relationship between the object distance

,u and the image distance , v.

Hypothesis:

3.5.4 Experiment to determine the focal As the object distance ,u increases ,the
length of a convex lens by using the thin lens image distance,v decreases.
equation
Aim of the experiment :
Aim of the experiment
To investigate the relationship between the
To determine the focal length of a convex object distance ,u and the image distance, v.
lens by using the thin lens equation
Variables in the experiment:
List of apparatus and materials
Convex lens, lens holder , white screen and Manipulated variable: object distance, u
ruler, cardboard with a cross-wire in a triangular Responding variable:image distance,v
cut-out(object) .
Arrangement of the apparatus: Constant variable: focal length of the lens, f

List of apparatus and materials:

Convex lens, lens holder , white screen and
ruler, cardboard with a cross-wire in a
triangular cut-out(object),

39

Arrangement of apparatus Example 6

An object of height 6 cm is placed at 20 cm
froma concave lens of focal length 40 cm.

The procedure of the experiment which (a) Calculate
include the method of controlling the (i) the image distance
manipulated variable and the method of (ii) the image height
measuring the responding variable. (iii)the linear magnification

The distance between the object and the (b) State the characteristics of the image
convex lens is measured by using a ruler , formed
u = 20 cm
The bulb is lighted up Solution
The screen is moved back and forth until a
sharp image is formed on it. Example 7
The distance between the screen and the lens
is measured , v. An object is placed 20 cm in front a lens. The
The experiment is repeated 4 times for the lens produced an image 4 times bigger than
other object distances ,u= 30 cm , 40 cm., 50 objectalso located in front the lens.
cm and 60 cm. (a) Determine the focal length of the lens
(b) What type of lens is used.
Tabulate the data:
Solution
u(cm) 20 30 40 50 60
v(cm) 3.6 Some important facts about lenses
Analysis the data:
1 A real image is one which can be formed on a
Plot the graph v against u
screen. while a virtual image is one which

cannot be formed on a screen.

2 When part of a lens is blocked by an object,
. the size and position of the image is the same as

before. The brightness of the image, however ,
is reduced.

3.5 To solve some problem involving the thin 3 The larger the diameter of a lens , the larger the
lens equation amount of light enter the the lens and as a result
the brighter the image formed.
Example 5
3.7 Optical devices use lenses
An object of height 2 cm is placed at 30 cm
from a convex lens of focal length 20.0 cm. 3.7.1 Introduction
(a) Calculate There are many types of optical devices used
(i) the image distance lenses such as magnifying glass, microscope,
(ii) the linear magnification telescope, camera in smart phone or
(iii)the image height CCTV,photocopier machine ,slide projector
(b) State the characteristics of the image formed etc.
For every types of the devices we must learn
Solution about the uses of the instruments, lens
characteristics is used, normal adjustment of
the instruments , ray diagrams and the
characteristics of the final image which are
formed .

40

3.7.2 Magnifying glass

Function To magnify image of an

object

Structure A thick convex lens

Normal Object distance, u <

adjustment focal length , f

Ray diagram ?

Characteris tics ?

of final image

Example 8

Complete ray diagram for the magnifying as
shown below and state the characteristics of the
final image.

Solution:

Solution

3.7.3 Telescope

Function To see a distant object (
object at infinity)
Structure Objective lens ( very long
focal length)
Normal Eyepiece : (very short focal
adjustment length)
fo >>>> fe
Magnification of Fo and Fe at same point
telescope or the distance between
Ray diagram two lenses = fo + fe
Characteris tics
of final image m  fo
fe

?
?

Example 9

Complete ray diagram for the telescope as
shown below and state the characteristics of the
final image.

41

3.7.4 Compound microscope Solution

Function To see a tiny object
Structure Objective lens ( short focal
length)
Normal Eyepiece : (short focal
adjustment length)

fe > fo
Normal adjustment : fo <
u < 2fo

Ray diagram ?
Characteris tics ?
of final image

Example 10

Complete ray diagram for the compound
microscope as shown below and state the
characteristics of the final image.

3.7.5 Small size lens in optical equipment
technology

Function As a main component of a high
resolution camera in smart

phone and CCTV
to capture and record pictures.

Structure Small size of convex lens. The
minimum distance between
Normal optical centre of lens and sensor
adjustment = the focal length of the lens.
Ray A sensor or mirror are used to
diagram flip the inverted image to the
Characteris upright image
tics of final Object distance u > 2f
image
?

?

42

Example 11 3.7.6 Convex lens as a paper burner
Complete ray diagram for the camera as
shown below and state the characteristics of Function To burn small pieces of paper or
the final image. dried leaves
Structure A thick convex lens
Solution Normal Object distance, u = 
adjusment
Ray diagram ?
Characteristics ?
of final image

Example 12

Complete the ray diagram of a convex lens using
sunlight to burn the paper as shown in the diagram
below and state the characteristics of final image

Solution

43

TUTORIAL 3 3 5 Which of the following drawing is not correct
path of the light rays?
1 The image produced by a lens is caused by the

A total internal reflection of ray
B diffraction of ray
C refraction of ray
D reflection of ray

2 Which of the following acts as lens except

A The surface of water waves 6 Diagram show light rays passing through a
B Glass block in rectangular shaped concave lens.
C The glass stem of thermometer in curved-

shaped
D The tranparent liquid in trasparent curved –wall

in plastic drinking bottele

3 Which diagram is true when rays of light passing
through a liquid in a bottle.

Which of the ray of light passing through the
optical centre of the lens?

AJ BK
CL DM

7 Diagram shows ray diagram of a convex lens.

Which part in the diagram represents image
distance?

4 Diagram shows a combination of two mediums AI B II
with different optical density. C III D IV

Which diagram is true when the rays of light 8 Diagram shows four light rays A,B,C and D
passing trough the combination of mediums? passing through a convex lens. F is the focal
point of the lens. Which of the following path
of the light rays is not correct?

9 Which diagram shows the correct refraction of
light ray after passing through a lens?

44

10 Diagram shows ray diagram of a concave lens 14 Which ray diagram is correct for a convex
in which F is the focal point. lens?

Which of the following equation is true?

A OQ  OP B OQ  OP
IJ IP IP IJ

C OQ x IJ  OP x IP D OQ x OP  IJ x IP

11 Diagram shows the ray diagram for a convex
lens.Which point is the focal point of the lens?

12 Diagram shows the ray of light passing
through a concave lens.

Which of the point A, B, C or D, is the 15 Diagram shows an image ,I is formed by a
focal point of the lens? convex lens. Where is the position of the object?

13 Which ray diagram is correct for a concave 16 Diagram shows an image ,I is formed by a
lens? concave lens. Where is the position of the
object?

17 Diagram shows the position of image formed by
a convex lens.

45

At which position the observer can see the After travelling through the lens the rays of light
image? is

A P and Q A parallel
B P and S B diverged
C R and S C converged
D Q and R D converged and diverged

18 A convex lens of focal length ,f. The lens 22 Diagram shows an object placed in front of a
produces a magnified , virtual and upright convex lens.
image. The object distance is
What are the characteristics of the image
A less than f formed?
B between f and 2f
C same as 2f A Real, inverted, diminished
D more than 2f B Virtual, inverted, same size
C Virtual, upright, enlarged
19 Diagram shows an object is placed in front of a D Real, inverted, enlarged
convex lens. 23 The height of image formed by a convex lens of
focal length , f has same height of the object.
Based on diagram , what is the characteristics The object distance, u is
of the image formed?
A u<f
A Magnified , inverted , real B u=f
B Diminished , upright , virtual C u = 2f
C Magnified , upright , virtual D u > 2f
D Diminished ,inverted ,real
24 Diagram shows a convex lens of focal length f.
20 Diagram shows an object placed in front of a At what point the object should be placed to
convex lens. produce real , inverted and diminished image.

At which position is the focal points of the lens? 25 The image produced by a concave lens is,

A J and L A enlarged, virtual, upright
B J and M B diminished, virtual, upright
C K and L C enlarged, real, inverted
D K and M D diminished, real, inverted

21 Diagram shows a bulb is placed in front a 26 Diagram shows an object is placed in front of a
convex lens at a distance same as the focal concave lens at point P produced smaller ,
length of the lens. upright and virtual image.
F is the focal point of the lens.

46

What is the characteristis of the image when 31 An object is placed at a distance of 30.0 cm
the object is placed at point Q? from a convex lens with a focal length of 25.0
cm.What is the linear magnification ?
A bigger , upright , real
B bigger , inverted , virtual A2 B3
C smaller , inverted , real C4 D5
D smaller , upright , virtual
32 An object is placed at 18.0 cm from a convex
27 Diagram shows a ray diagram of a convex lens of focal length 20.0 cm.
lens. What is the characteristics of image ?

A virtual, upright and magnified
B real, inverted and magnified
C virtual ,upright and diminished
D real, inverted and diminished

What is the focal length of the lens? 33 Diagram shows ray diagram for a convex
lens.

A 15.0 cm B 24.0 cm
C 24.3 cm D 30.0 cm

28 An object is placed at 12.0 cm from a concave Which of the following is not true?
lens of focal length 20.0 cm.What is the image
distance? A The height of object is equal to the height of
the image
A 30.0 cm in front of the lens
B 30.0 cm behind the lens B The focal length of the lens is 80 cm
C 7.5 cm in front of the lens C The linear magnification is 1
D 7.5 cm behind the lens D The image is a real image

29 Diagram shows an image of an object is 34 An object is placed 25 cm in front of a convex
formed by a convex lens. lens and its image is formed at infinity. If the
object is placed 40 cm in front of the lens , the
image is

What is the linear magnification of the image? A inverted , magnified , virtual
B upright , diminished , real
A 0.5 B 1.0 C inverted , magnified , real
C 3.0 D 4.0 D upright , diminished, virtual

30 Diagram shows a ray diagram a convex lens. 35 A convex lens of focal length 30.0 cm is turned
to face a distant object. The position of the
screen is adjusted until a sharp inverted image is
formed on the screen.What is the distance of the
screen from the lens ?

A 15.0 cm B 30.0 cm
C 45.0 cm D 60.0 cm

36 The image of an object located 80.0 cm in front
for a concave lens with a focal length of 20.0
cm is

Based on diagram , what is the value of H? A 16.0 cm at the same side of the object.
B 16.0 cm at the opposite side of the object.
A 6.7 cm B 9.6 cm C 26.7 cm at the same side of the object.
C 15.0 cm D 21.6 cm D 26.7 cm at the opposite side of the object.

47

37 Diagramshows an object which is placed at Based on the graph ,what is the focal length,f of
u cm from centre of a convex lens. The focal the lens?
length of the lens is 30 cm.

A 0.02 cm B 0.04 cm
C 50.0 cm D 100.0 cm

Which of the following characteristics of the 40 A convex lens is used to produce a real,
magnified and inverted image. What is the
image is not correct when u is 20 cm ,30 cm , effect on the image produced when the upper
portion of the lens is covered by a coin ?

40 cm and 70 cm from the lens?

u (cm) Characteristics of the A The upright image is formed
B The diminished image is formed
image C The size of the image is reduced
D The brightness of the image is reduced
A 20 Virtual and bigger

B 30 Virtual and bigger

C 40 Real and smaller

D 70 Real and smaller 41 Diagram shows an ant is seen through a
magnifying glass.
38 Diagram shows the apparatus used to determine

the relationship between the object distance, u,

the image distance, v, and the focal length, f, of

a convex lens.

Which of the following combinations is true for
the magnifying lens ?

Distance between ant Focal length

and magnifying glass of magnifying

(cm) glass (cm)

The results are shown in graph below. . A5 10

B8 5

C 10 5

D 20 8

42 A lens has a focal length f.
What are the required conditions for the lens to
be used as a magnifying lens?
Type of lens Object distance

What is the value of p?

A 1f B1 A Concave Less than f
2 f B Concave More than f
C Convex Less than f
Cf D 2f D Convex More than f

39 The equation of a thin lens is given by the 43 Which of the following ray diagrams is correct
equation : 1  1  1 for a magnifying glass?
fu v

48

Linear Distance between
magnification lenses
(cm)
A 250 45
B 250 55
C 10 45
D 10 55

47 The diagram shows the design of a simple
astronomical telescope.

Which characteristics of images formed by lens
P and lens Q.

Charateristics of Charateristics of
image P image Q
A virtual, upright virtual , upright
B real, inverted virtual , inverted
C virtual, inverted real, inverted
D real, upright real, inverted

44 Which of the following pairs of lens are used to 48 Which arrangement of objective lens, Lo.
construct a telescope? eyepiece, Le and position of image I, is correct
for a telescope at normal adjustment?

A A concave lens of focal length 3 cm and a
concave lens of focal length 120 cm

B A convex lens of focal length 3 cm and a
convex lens of focal length 120 cm

C A concave lens of focal length 100 cm and a
concave lens of focal length 120 cm

D A convex lens of focal length 100 cm and a
convex lens of focal length 120 cm

45 Two convex lens lens W and lens X of focal
lengths 40 cm and 5 cm respectively is used in
a telescope.
Which of the following is true?

Objective Eyepiece Distance

lens between lens W

and X at normal

adjusment (cm)

AW X 35

BX W 35

CW X 45

DX W 45

46 A telescope has two convex lens of focal
length 5.0 cm and 50 c respectively.Which
of the following is true?

49

49 Choose the most suitable combinations of the 52 Diagram shows ray diagram of a camera.
lens that be used to construct a microscope.

Objective lens Eyepiece

A Concave lens of Concave lens of

focal length 3 cm focal length 120 cm

B Convex lens of Convex lens of
focal length 3 cm focal length 120 cm

C Concave lens of Concave lens of Based on diagram which of the following is
focal length 3 cm focal length 5 cm
true?

A u<f B u=f

D Convex lens of Convex lens of C f < u < 2f D u > 2f
focal length 3 cm focal length 5 cm

53 Diagram 53 shows a water droplet on a piece
of wax paper with writing on it.

50 Which of the following is the correct positions
of the object and the final image of a compound
microscope at a normal adjusment?

51 What is the characteristics of image formed by Diagram 53
lens in a digital camera. (a) State the phenomenon of light involved.
A virtual, upright and magnified
B real, inverted and magnified ........................................................................
C real, inverted and diminished [ 1 mark ]
D virtual ,upright and diminished
(b) The image of writing look bigger when
50 viewed through the water droplet.
(i) Why the image of the writing look bigger
..................................................................
..................................................................
[ 2 marks ]
(ii) State the two other characteristics of the
image of the writing.
..................................................................
[ 1 mark ]

(c) What is the change size of the image of the
writing when the water droplet is replaced
with a transparent liquid droplet of a
greater optical density?
..................................................................
[ 1 mark ]

(d) The water droplet is replaced with a lens
with focal length of 20 cm. The distance
between the writing and the centre of the
lens is 10 cm.It is observed that the image
of the writing is enlarged.

(i) Name the type of the lens.
…………………………………….....
[ 1 mark ]