Name: ___________________ (
)
Class: ______
F3 I.S.
Remedial programme
Problem set 04/10
Date: ___________
Score:
/ 30
Unit 3 Light, colors and beyond
A
True or false questions (6 marks, 1 mark each)
Write ‘T’ for a true statement and ‘F’ for a false statement in the boxes provided.
1
White light consists of 7 different colours

2 Swimming pools look shallower than they really are because of total internal
reflection of light.
3
When a light ray passes form one medium to another, it is refracted because
the speed of light is different in the two different media.
4


A light ray is bent away from the normal when it passes from a less dense
medium to a denser medium.

5
Total internal reflection occurs when light travels from air to glass.

6
Total internal reflection occurs if the angle of incidence is smaller than the
critical angle.

1
B
Multiple-choice questions (6 marks, 2 marks each)
Choose the correct answer for each of the following questions.
1
A beam of light travels from a crystal to air as shown. What is the refractive index
of the crystal?
A.
B.
C.
D.
0.78
0.93
1.08
1.98

2
Which of the following about the laws of refraction are incorrect?
(1) The angle of refraction r is always equal to the angle of incidence i.
(2) The ratio of the sine of the angle of incidence to the sine of the angle of
refraction is always equal to 1, that is,
sin i
1.
sin r
(3) The incident ray, the reflected ray and the normal all lie in the same plane.
A
B
C
D
(1) and (2) only
(1) and (3) only
(2) and (3) only
(1), (2) and (3)

2
3
The following diagrams shows a light ray hitting a semicircular glass block in
different ways. C is the center of the semicircular block. Which diagram(s) is/are
correct? (Take critical angle of glass = 42.)
(1)
(2)
(3)
A
B
C
D
(2) only
(1) and (2) only
(1) and (3) only
(1), (2) and (3

C Fill in the blanks (6 marks, 1 mark each)
Complete the following sentences.
1
On hot and sunny days, drivers on a highway may see water ponds which is
actually the images of clouds in the sky. This phenomenon is called
__________________.
2
A ______________mirror has a silver surface at the back of the glass sheet. The mirror
gives multiple images due to_______________ reflections inside the glass.
These
multiple images are very faint and cause unclearance in optical instruments such
3
as cameras and telescopes.
3
____________________are widely used in telecommunication for signal
transmission.
4
When a beam of white light passes through a prism, it is separated into a range of
colours. This phenomenon is known as____________________.
5
The band of coloured lights obtained is called the colour ____________of light. It
consists of red, orange, yellow, green, blue, indigo and violet.
D Questions (12 marks)
1
A ray of light enters a glass block from air as shown.
50
air
glass
30
(a) Find the refractive index of the glass.
(1 mark)
(b) If the light ray enters the glass from air with an angle of incidence of 60, find
the angle of refraction.
(1 mark)
4
2
A light ray emerges from water into air as shown. The refractive index of water is
1.33.

air
water
35
(a) Find .
(b) Find the critical angle of water.
3
(1 mark)
(2 marks)
Alex tries to catch a fish in the water using a spear. His experience tells him that he
should not aim at the position where the fish appears to be. Briefly explain why.
You may illustrate your explanation with the aid of a diagram.
(2 marks)
5
4. A ray of light strikes the glass-air boundary as shown below. Afterwards, part of the
light ray is reflected and part of the light ray travels into air.
Suppose the refractive index of the glass is 1.51.
(a) Find the angle of reflection and the angle of refraction.
(3 marks)
(b) If the light ray strikes the glass-air boundary at an angle of incidence of 65°, how
does the light travels afterwards? Illustrate your answer with the aid of a
diagram.
(2 marks)
- End –
6
Answers
Unit 3 Light, colors and beyond
F3 I.S.
Remedial programme
Problem set 04/10
A True or false questions (6 marks, 1 mark each)
1 T
2 F
3 T
4 F
5 F
6 F
B Multiple-choice questions (6 marks, 2 marks each)
1 D
2 A
3 C
C Fill in the blanks (6 marks, 1 mark each)
Mirage
Plane, multiple
Optical fiber
Dispersion
Spectrum
D Questions (12 marks)
Answer:
1
Solutions
(a) Refractive index =
=
Marks
sin  a
sin  g
sin 50
sin 30
= 1.532
 1.53
(b) Refractive index =
1.532 =
1A
sin  a
sin  g
sin 60
sin  g
 g = 34.4
1A
 The angle of refraction is 34.4.
7
Solutions
(a) By n =
sin  a
,
sin  g
1.33 =
sin 
sin 35
 = 49.7
Marks
1A
 1
(b) Critical angle = sin1  n 
1M
 1 
= sin  1.33 
1 
1A
= 48.8
3. As shown in the diagram below, the fish appears to be nearer to the observer (1A). Hence, if one
aims at the apparent position of the fish, one could hardly catch the fish
(1A)
(a) The angle of reflection is 32°.
From the definition of refractive index,
sin i
sin r
sin 32
1.51 
sin r
r  20.54
(1A)
n
(1M)
The angle of refraction r is 20.5°.
(1A)
(b) Total internal reflection occurs in this case. The light ray will undergo total internal reflection when
it strikes the glass-air boundary.
(1A)
(1A)
8