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Question Bank (Ch. 15)
INTERACTIVE SCIENCE 3C
Question Bank
Chapter 15
LIGHT, COLOURS AND BEYOND
Concept Checking
Write ‘T’ for a true statement or ‘F’ for a false statement.
15.1
How We See an Object
3C150101Q001Eng
Luminous objects are ‘luminous’ because they reflect light from other light sources.
[Ans]
F
3C150101Q002Eng
Non-luminous objects cannot be seen as they do not emit light.
[Ans]
F
3C150201Q003Eng
When the Moon is in the middle of the Sun and the Earth, the Moon blocks the sunlight. Therefore, at some
places on the Earth, people cannot receive the reflected sunlight from the Moon, and this results in lunar
eclipse.
[Ans]
F
3C150101Q004Eng
We can see stars because they reflect light from the Sun.
[Ans]
F
3C150101Q005Eng
The Sun is the largest luminous object in our solar system.
[Ans]
T
3C150101Q006Eng
Light travels along a straight line.
[Ans]
T
3C150101Q007Eng
No matter at what time during the day, our shadow is in front of us and its shape does not change.
[Ans]
15.2
F
Reflection at Plane Surfaces
3C150101Q008Eng
Dust particles can help us observe the route of laser light through reflection.
[Ans]
T
3C150101Q009Eng
Reflection of light can only occur at smooth surfaces.
[Ans]
F
3C150101Q010Eng
The angle of reflection is the angle between the incident ray and the reflected ray.
[Ans]
F
3C150101Q011Eng
On reflection, angle of incidence is always greater than the angle of reflection.
[Ans]
F
3C150101Q012Eng
In diffuse reflection, parallel light rays are reflected in different directions.
[Ans]
T
142
Question Bank (Ch. 15)
3C150101Q013Eng
The image of an object formed by a plane mirror is laterally inverted and magnified.
[Ans]
F
3C150101Q014Eng
If an object is 1 m from a plane mirror, the image formed is 2 m from the object.
[Ans]
T
3C150101Q015Eng
If a man moves to his right in front of a mirror, his image formed will also move to its right.
[Ans]
F
3C150101Q016Eng
Mirrors can be used as energy-saving devices to reflect sunlight into a building.
[Ans]
T
3C150101Q017Eng
The image formed by a periscope is upright.
[Ans]
T
3C150101Q018Eng
The design of rare-view mirror is very special. The image formed is upright and not laterally inverted.
[Ans]
F
3C150101Q019Eng
Plane mirrors can make a room look more spacious.
[Ans]
15.3
T
Colour
3C150101Q020Eng
Prism can disperse white light to form a colour spectrum.
[Ans]
T
3C150101Q021Eng
Colour spectrum consists of seven colours only  red, orange, yellow, green, blue, indigo and violet.
[Ans]
F
3C150101Q022Eng
After rain, water droplets in air disperse the sunlight that enters them into a colour spectrum. This is how a
rainbow is formed.
[Ans]
T
3C150101Q023Eng
Primary colours of light are red, blue and green.
[Ans]
T
3C150101Q024Eng
White light can be produced by mixing red, blue and green lights.
[Ans]
T
3C150101Q025Eng
A red object appears green under green light.
[Ans]
F
3C150101Q026Eng
Mixing red and blue lights can get magenta light.
[Ans]
T
3C150101Q027Eng
When white light shines on a black object, red, blue and green lights are reflected.
[Ans]
F
143
Question Bank (Ch. 15)
3C150101Q028Eng
People with total colour blindness see either black or white objects only.
[Ans]
F
3C150101Q029Eng
People suffer from colour blindness because the rods on the retina have difficulties in detecting coloured
lights.
[Ans]
F
3C150101Q030Eng
Trauma (創傷) in our brain may cause colour blindness.
[Ans]
F
3C150101Q031Eng
Colour blindness can be detected and cured by surgery.
[Ans]
F
15.4 Beyond the Visible Spectrum
3C150101Q032Eng
Infrared radiation and ultraviolet radiation are members of visible spectrum.
[Ans]
F
3C150101Q033Eng
We feel warm after we absorb infrared radiation.
[Ans]
T
3C150101Q034Eng
Ultraviolet radiation will make fluorescent materials glow.
[Ans]
T
3C150101Q035Eng
We get a tan because of ultraviolet radiation from the Sun.
[Ans]
T
3C150101Q036Eng
We can measure the body temperature by measuring the infrared radiation emitted by the body.
[Ans]
T
3C150101Q037Eng
Infrared detectors can be used to check bank notes.
[Ans]
F
3C150101Q038Eng
(extension) Ozone layer can reduce the ultraviolet radiation from the Sun.
[Ans]
T
3C150101Q039Eng
Ultraviolet can be used for cancer treatment.
[Ans]
F
3C150101Q040Eng
(extension) CFCs in aerosol sprays can react with ozone molecules and damage the ozone layer.
[Ans]
T
15.5 Beyond Infrared and Ultraviolet Radiations
3C150101Q041Eng
Among all members of the EM spectrum, radio waves have the longest wavelength.
[Ans]
T
3C150101Q042Eng
Among all members of the EM spectrum, gamma rays have the highest frequency.
[Ans]
T
144
Question Bank (Ch. 15)
3C150101Q043Eng
Gamma rays are emitted by electrons of radioactive atoms.
[Ans]
F
3C150101Q044Eng
Radio waves have the highest frequency and energy among all EM waves. Thus they cannot be used in any
daily applications.
[Ans]
F
3C150101Q045Eng
X-rays can be used to sterilise food.
[Ans]
F
3C150101Q046Eng
Radar makes use of reflection of waves to detect objects.
[Ans]
T
3C150201Q047Eng
Bluetooth wireless technology makes use of microwaves for communication.
[Ans]
T
3C150101Q048Eng
The frequency of radio waves used in AM broadcasting is higher than that in FM broadcasting.
[Ans]
F
3C150101Q049Eng
Television uses microwaves for broadcast.
[Ans]
F
3C150101Q050Eng
When mobile phones are in use, radios and televisions nearby could be interfered.
[Ans]
15.6
T
Refraction and Its Practical Uses
3C150201Q051Eng
(extension) When light travels from air to glass at right angles to the interface, the angle of refraction is
smaller than the angle of incidence.
[Ans]
F
3C150201Q052Eng
(extension) Put a glass plate on newspaper. The words under the glass plate seem to rise up to a higher level.
[Ans]
T
3C150201Q053Eng
(extension) Refraction occurs in lenses only.
[Ans]
F
3C150101Q054Eng
(extension) Owing to the reflection of light, one finds that the water of a swimming pool is actually deeper
than what he observes from the side.
[Ans]
F
3C150201Q055Eng
(extension) Convex lens can form upright images as well as inverted images.
[Ans]
T
3C150101Q056Eng
(extension) Convex lens can be used as a magnifying glass.
[Ans]
T
145
Question Bank (Ch. 15)
15.7
Optical Fibres and Total Internal Reflection
3C150201Q057Eng
(extension) When a light ray is directed from glass to air, total internal reflection occurs if the angle of
refraction is smaller than a certain value.
[Ans]
F
3C150101Q058Eng
(extension) Total internal reflection may occur when light travels from air to water.
[Ans]
F
3C150101Q059Eng
(extension) Optical fibres work on the principle of total internal reflection.
[Ans]
T
3C150101Q060Eng
(extension) We can turn the direction of a light ray by 90 or 180 by using one right-angled prism.
[Ans]
T
Multiple Choice
Circle the best answer for each question below.
15.1
How We See an Object
3C150102Q001Eng
Which of the following is/are luminous object(s)?
(I)
Fireflies (螢火蟲)
(II)
The Moon
(III) The Sun
A.
(III) only
B.
(I) and (III) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
B
3C150102Q002Eng
Which of the following about light is/are correct?
(I)
Light travels in a straight line.
(II)
The travelling direction of light cannot be changed.
(III) We can see only if light enters our eyes.
A.
(I) only
B.
(I) and (III) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
B
3C150102Q003Eng
For the light ray below, which of the following reflected ray is correct?
A.
B.
146
Question Bank (Ch. 15)
C.
[Ans]
D.
B
3C150202Q004Eng
Which of the following diagrams about reflection is NOT correct?
A.
B.
C.
D.
[Ans]
15.2
D
Reflection at Plane Surfaces
3C150102Q005Eng
Paul is standing in front of a quiet lake and there is a mountain behind the lake. He can see the image of the
mountain at the lake surface. Which of the following about that image is NOT correct?
A.
That image is formed by the reflection at the lake surface.
B.
That image is vertically inverted.
C.
That image is laterally inverted.
D.
The size of that image is the same as that of the mountain.
[Ans]
C
3C150102Q006Eng
Which of the following statements is correct?
A.
Reflection only occurs at smooth surfaces.
B.
Only smooth surfaces can form images by reflection.
C.
Laws of reflection can only be applied to the reflection at smooth surfaces.
D.
[Ans]
Rough surfaces would absorb all light that shines on them and no light would be reflected from them.
B
3C150202Q007Eng
What is the angle of reflection for the following light ray?
20
A.
20
B.
70
C.
90
D.
160
[Ans]
B
147
Question Bank (Ch. 15)
3C150202Q008Eng
A girl is standing in front of a plane mirror. If she walks 30 cm closer to the mirror, what is the change in the
distance between the girl and her image?
A.
Decreases by 30 cm
B.
Decreases by 60 cm
C.
Increases by 30 cm
D.
Increases by 60 cm
[Ans]
B
3C150202Q009Eng
A room has two pieces of mirror as shown below. Both the length and the width of the room are 3 m. If
Mandy stands in the corner below, how large does the room looks to her?

Mandy
A.
3 m of length by 3 m of width
B.
3 m of length by 6 m of width
C.
6 m of length by 3 m of width
D.
6 m of length by 6 m of width
[Ans]
D
3C150102Q010Eng
Stephen stands in front of a plane mirror. He holds a comb with his right hand and leans closer to the mirror
by 20 cm. Which of the following statements are correct?
(I)
His mirror image is upright.
(II)
The distance between Stephen and his mirror image is 40 cm.
(III) The mirror image of Stephen holds the comb with his left hand.
A.
(I) and (II) only
B.
(I) and (III) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
B
3C150102Q011Eng
Which of the following statements about the laws of reflection is/are correct?
(I)
The incident ray, the normal and the reflected ray all lie in the same plane.
(II)
The angle of reflection is greater than the angle of incidence.
(III) The normal of the mirror is a line on the mirror surface.
A.
(I) only
B.
(I) and (II) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
A
3C150102Q012Eng
Which of the following statements about plane mirror images is/are correct?
(I)
Images are vertically inverted.
(II)
Images are virtual.
(III) Images are magnified.
A.
(II) only
B.
(I) and (II) only
C.
(I) and (III) only
D.
(I), (II) and (III)
[Ans]
A
148
Question Bank (Ch. 15)
3C150102Q013Eng
Which of the following is/are application(s) of plane mirrors?
(I)
Rear-view mirrors
(II)
Periscopes
(III) Magnifying glasses
A.
(I) only
B.
(I) and (II) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
B
3C150202Q014Eng
Which of the following diagrams correctly shows the situation when sunlight passes through a prism?
A.
B.
sunlight
sunlight
sunlight
sunlight
glass
prism
glass
prism
Sunlight leaves the prism with a change in
d i r e c t. i o n
Sunlight leaves the prism with a change in
direction.
C.
D.
sunlight
sunlight
red
glass
prism
blue
Light rays in primary colours are produced.
[Ans]
red
glass
prism
green
violet
A band of colour lights is produced.
D
3C150102Q015Eng
Which of the following colours CANNOT be found in the colour spectrum?
A.
Indigo
B.
Green
C.
Yellow
D.
Black
[Ans]
D
3C150202Q016Eng
If a rainbow is formed when the Sun is in the East, towards which direction should we look in order to see the
rainbow?
A.
East
B.
South
C.
West
D.
North
[Ans]
C
15.3
Colour
3C150202Q017Eng
What is the minimum number of colour lights required to produce white light?
A.
1
B.
2
C.
3
D.
7
[Ans]
B
149
Question Bank (Ch. 15)
3C150102Q018Eng
What are the three primary colours of light?
A.
Red, yellow and blue
B.
Yellow, green and blue
C.
Yellow, cyan and magenta
D.
Red, green and blue
[Ans]
D
3C150202Q019Eng
Which of the following mixtures of lights would result in white light?
(I)
Red + green + blue
(II)
Magenta + cyan + yellow
(III) Yellow + blue
A.
(I) only
B.
(II) only
C.
(I) and (III) only
D.
(I), (II) and (III)
[Ans]
D
3C150202Q020Eng
Which of the following colour of light CANNOT be produced by mixing lights of primary colours?
A.
White
B.
Black
C.
Violet
D.
Brown
[Ans]
B
3C150102Q021Eng
What is the function of the electron guns in a colour television?
A.
To emit electron beams towards the screen
B.
To form images on the screen by emitting red, blue and yellow lights
C.
To heat up the screen
D.
To amplify the signals received from the antenna
[Ans]
A
3C150102Q022Eng
What covers the inner surface of a colour television screen?
A.
Sulphur strips
B.
Phosphor strips
C.
Potassium strips
D.
Iron strips
[Ans]
B
3C150102Q023Eng
Which of the following colours of light is absorbed by a piece of cyan paper when sunlight shines on it?
A.
Cyan
B.
Red
C.
Blue
D.
Blue and green
[Ans]
B
3C150102Q024Eng
A red apple with a green leaf is placed on a black table. What will they appear if green light shines on them?
A.
A green apple with a green leaf on a green table.
B.
A red apple with a red leaf on a red table.
C.
A black apple with a green leaf on a black table.
D.
Everything is in black.
[Ans]
C
150
Question Bank (Ch. 15)
3C150202Q025Eng
Nancy looks at a piece of red paper through a filter and the paper appears red. What could the colour of the
filter be?
(I)
Green
(II)
Magenta
(III) Yellow
A.
(II) only
B.
(III) only
C.
(I) and (III) only
D.
(II) and (III) only
[Ans]
D
3C150202Q026Eng
Mandy sees a green pen through a cyan filter. Which of the following CANNOT be the actual colour of the
pen?
(I)
Green
(II)
Magenta
(III) Yellow
A.
(II) only
B.
(I) and (III) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
A
3C150102Q027Eng
What is the function of cones in the eyes?
A.
They focus light on the retina.
B.
They provide nutrition to the retina.
C.
They are responsible for colour vision.
D.
They are responsible for vision in the dark.
[Ans]
C
3C150102Q028Eng
Which of the following is the cause of colour blindness?
A.
Malfunction of the rods of eyes
B.
Malfunction of the cones of eyes
C.
Malfunction of the lenses of eyes
D.
Malfunction of the pupils of eyes
[Ans]
B
3C150202Q029Eng
What would people with red-green colour blindness see if they look at traffic lights?
A.
They cannot see the lights clearly.
B.
They see the green light as red and the red light as green.
C.
Based on the colour only, they cannot tell the red light from the green.
D.
They see the lights the same as normal people.
[Ans]
C
3C150102Q030Eng
Which of the following statements about the people suffered from colour blindness is correct?
A.
They cannot see things clearly.
B.
They can only see things in black and white.
C.
They cannot distinguish some colours.
D.
They can be cured.
[Ans]
C
151
Question Bank (Ch. 15)
3C150102Q031Eng
Which of the following shows the right order of wavelength of waves?
A.
Infrared > visible light > ultraviolet > gamma rays
B.
X-ray > visible light > microwaves > radio waves
C.
Radio waves > ultraviolet > microwaves > X-ray
D.
Microwaves > ultraviolet > infrared > gamma rays
[Ans]
A
15.4 Beyond the Visible Spectrum
3C150102Q032Eng
Which of the following are the applications of infrared radiation?
(I)
Detectors for searching for illegal immigrants.
(II)
Thermometers
(III) Remote controls
A.
(I) and (II) only
B.
(I) and (III) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
D
3C150102Q033Eng
Which of the following radiations is made use in some thermometers?
A.
X-rays
B.
Ultraviolet radiation
C.
Microwaves
D.
Infrared radiation
[Ans]
D
3C150202Q034Eng
Which of the following is/are the reason(s) why night vision devices and some detectors make use of infrared
radiation?
(I)
(II)
A lot of living things and objects emit infrared radiation.
The infrared radiation emitted by objects or living things changes with the temperature of the objects.
(III) Infrared radiation can penetrate through many objects.
A.
(I) only
B.
(II) only
C.
(I) and (II) only
D.
(I), (II) and (III)
[Ans]
D
3C150202Q035Eng
Which of the following characteristics of X-rays is commonly used in daily applications?
A.
Short wavelength
B.
High energy
C.
High penetrating power
D.
High frequency
[Ans]
C
3C150102Q036Eng
Which of the following is NOT the common use of ultraviolet radiation?
A.
Sterilising food
B.
Sterilising medical equipment
C.
Checking bank notes
D.
Scanning luggage at airports
[Ans]
D
152
Question Bank (Ch. 15)
15.5 Beyond Infrared and Ultraviolet Radiations
3C150102Q037Eng
(extension) Which of the following CANNOT protect us from ultraviolet radiation?
A.
Ozone layer
B.
Sun block
C.
Sunglasses
D.
CFCs
[Ans]
D
3C150102Q038Eng
(extension) Which of the following statements is/are correct?
(I)
The atmosphere of the Earth protects us from harmful radiation from the Sun.
(II)
The ozone layer of the atmosphere can be strengthened by CFC.
(III) The atmosphere of the Earth reflects some radiation.
A.
(I) only
B.
(I) and (II) only
C.
(I) and (III) only
D.
(I), (II) and (III)
[Ans]
C
3C150102Q039Eng
Which of the following is/are the use(s) of microwaves?
(I)
Microwave oven
(II)
Satellite communication
(III) Radar
A.
(I) only
B.
(I) and (II) only
C.
(I) and (III) only
D.
(I), (II) and (III)
[Ans]
D
3C150102Q040Eng
Which of the following radiations can be used to detect bone fractures?
A.
X-rays
B.
Gamma rays
C.
Microwaves
D.
Radio waves
[Ans]
A
3C150102Q041Eng
Study the following electromagnetic spectrum.
Radio
P
waves
Infrared
Visible
radiation
light
Q
low frequency
Gamma
R
rays
high frequency
What are P, Q and R?
P
Q
R
A.
Microwaves
Ultraviolet radiation
X-rays
B.
X-rays
Ultraviolet radiation
Microwaves
C.
Ultraviolet radiation
X-rays
Microwaves
D.
X-rays
Microwaves
Ultraviolet radiation
[Ans]
A
153
Question Bank (Ch. 15)
3C150102Q042Eng
The electromagnetic waves below are arranged in an order of their wavelengths.
Gamma
P
rays
Q
Visible
Infrared
light
radiation
R
Radio
waves
Which of the following statements about R is/are correct?
(I)
The frequency of R is higher than that of infrared radiation.
(II)
R can be used in satellite communication and radar.
(III) R can be used in cooking.
A.
(I) only
B.
(I) and (III) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
C
3C150102Q043Eng
Which of the following waves CANNOT pass through a vacuum?
A.
Gamma rays
B.
Sound waves
C.
Microwaves
D.
Ultraviolet radiation
[Ans]
B
3C150102Q044Eng
Which of the following statements about infrared radiation is correct?
A.
It is mainly emitted by cold objects.
B.
It makes a person look red.
C.
It cannot be seen by naked eyes.
D.
It makes fluorescent materials glow.
[Ans]
C
15.6
Refraction and Its Practical Uses
3C150102Q045Eng
Which of the following about ultraviolet radiation is correct?
A.
It makes us feel warm.
B.
It can kill bacteria.
C.
It has high penetrating power.
D.
It can be used in cooking.
[Ans]
B
3C150202Q046Eng
Light rays travel from region A to region B. In which of the following situation will NOT show refraction of
light?
Region A
Region B
A.
Air
Glass
B.
Glass
Water
C.
Diamond
Air
D.
Water
[Ans]
Water
D
3C150202Q047Eng
(extension) Which of the following diagrams correctly show(s) the path of light ray passing from air into
water?
(I)
(II)
(III)
water
water
water
air
air
air
154
Question Bank (Ch. 15)
A.
(I) only
B.
(II) only
C.
(I) and (II) only
D.
(I) and (III) only
[Ans]
D
3C150102Q048Eng
(extension) Which of the following is the correct refracted light ray?
air
D
A
glass
C
B
[Ans]
B
3C150102Q049Eng
(extension) Place a convex lens just above an object and allow the lens to just touch the object. Which of the
following about the image formed is/are correct?
(I)
The image is vertically inverted.
(II)
The image is laterally inverted.
(III) The image is magnified.
A.
(III) only
B.
(I) and (II) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
A
3C150102Q050Eng
(extension) Which of the following can be the device X in the diagram below?
X
A.
Mirror
B.
Triangular prism
C.
Convex lens
D.
Rectangular glass block
[Ans]
C
3C150102Q051Eng
(extension) Which of the following does NOT make use of convex lens(es)?
A.
Binoculars
B.
Magnifying glasses
C.
Microscopes
D.
Periscopes of buses
[Ans]
D
3C150202Q052Eng
(extension) Which of the following statements about a goldfish as viewed by an observer outside a fish tank is
correct?
A.
A goldfish seems smaller than its actual size.
B.
The size of a goldfish is the same as viewed by the observer.
C.
A goldfish seems closer to the observer than the actual distance.
D.
A goldfish seems farther away from the observer than the actual distance.
[Ans]
C
155
Question Bank (Ch. 15)
3C150102Q053Eng
(extension) Which of the following statements about the image formed by a microscope are correct?
(I)
The image is vertically inverted.
(II)
The image is laterally inverted.
(III) The image is magnified.
A.
(I) and (II) only
B.
(I) and (III) only
C.
(II) and (III) only
D.
(I), (II) and (III) only
[Ans]
D
3C150202Q054Eng
(extension) Mirages can be seen in deserts sometimes. Which of the following is the cause of mirage?
A.
Reflection of light
B.
Refraction of light
C.
Total internal reflection of light
D.
Total internal refraction of light
[Ans]
15.7
C
Optical Fibres and Total Internal Reflection
3C150202Q055Eng
(extension) Which of the following phenomena are responsible for the formation of rainbow?
(I)
Dispersion
(II)
Reflection
(III) Total internal reflection
A.
(I) and (II) only
B.
(I) and (III) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
A
3C150202Q056Eng
(extension) Which of the following diagram is correct?
A.
B.
C.
D.
[Ans]
B
3C150202Q057Eng
(extension) A light ray is emitted in water. Under which of the following conditions will total internal
reflection occur?
(I)
The light ray is directed from water to air.
(II)
The angle of incidence of the light ray is greater than the critical angle.
(III) The temperature of water is less than 30C.
A.
(I) only
B.
(I) and (III) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
B
156
Question Bank (Ch. 15)
3C150102Q058Eng
(extension) Which of the following is/are the application(s) of total internal reflection?
(I)
Optical fibres
(II)
Binoculars
(III) Safety reflectors placed at the back of a bicycle
A.
(I) only
B.
(I) and (III) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
D
3C150102Q059Eng
(extension) Which of the following is/are the application(s) of optical fibres?
(I)
Transfer of light
(II)
Endoscopes
(III) Telecommunication
A.
(I) only
B.
(I) and (III) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
D
3C150102Q060Eng
(extension) Which of the following is/are the difference(s) between using optical fibres and using copper
wires for transmitting signals in telecommunications?
(I)
Optical fibres lose less signals.
(II)
Optical fibres are more expensive.
(III) Optical fibres are difficult to bend.
A.
(I) only
B.
(I) and (II) only
C.
(II) and (III) only
D.
(I), (II) and (III)
[Ans]
A
Fill in the Blanks
15.1
How We See an Object
3C150103Q001Eng
Some objects give out light on their own. They are called _________ objects.
[Ans]
luminous
3C150103Q002Eng
A (a)____________ object does not give out light on its own. It can be seen because it (b)___________ light
from light sources into our eyes.
[Ans]
(a) non-luminous
(b) reflects
3C150103Q003Eng
In the solar system, the Sun is the only star and it is an example of (a)____________ objects, while Jupiter is
the heaviest planet and it is an example of (b)___________ objects.
[Ans]
(a) luminous
(b) non-luminous
3C150103Q004Eng
Light from an object is _____________ at the surface of a mirror and an image of the object is produced.
[Ans]
15.2
reflected
Reflection at Plane Surfaces
3C150103Q005Eng
For a plane mirror, the angle of incidence refers to the angle between the (a)___________ ray and the
(b)____________ .
[Ans]
(a) incident
(b) normal
157
Question Bank (Ch. 15)
3C150103Q006Eng
The laws of reflection: The incident ray, the (a)____________ and the (b)_____________ ray all lie in the
same plane. And the angle of (c)______________ is equal to the angle of (d)_____________ .
[Ans]
(a) normal
(b) reflected
(c) reflection
(d) incidence
3C150103Q007Eng
When parallel light rays fall on rough surfaces, they are reflected in different directions. This type of
reflection is called ______________________ .
[Ans]
diffuse reflection
3C150103Q008Eng
When parallel light rays fall on smooth surfaces, they are reflected in the same direction. This type of
reflection is called ______________________ .
[Ans]
regular reflection
3C150103Q009Eng
Only (a)______________ surfaces allow for (b)_____________ reflections to form images.
[Ans]
(a) smooth
(b) regular
3C150103Q010Eng
Characteristics of an image formed by a plane mirror:
 The image is (a)______________ .
 The distance between the object and the mirror is (b)______________ (greater than / equal to / smaller than)
the distance between the image and the mirror.
 The image is (c)________________ inverted.
[Ans]
(a) upright / erect
(b) equal to
(c) laterally
3C150103Q011Eng
If an object is placed at 1 m in front of a plane mirror, the image is ______________ from the object.
[Ans]
2m
3C150103Q012Eng
Write a "p" on a paper and erect the paper above a horizontal plane mirror. The image formed by the plane
mirror is ______________ .
[Ans]
b
3C150203Q013Eng
Write a "p" on a flat paper and erect a plane mirror beside "p". The image formed by the plane mirror is
______________ .
[Ans]
q
3C150103Q014Eng
The image of plane mirror cannot be projected on a screen. This type of mirror is called _______________ .
[Ans]
virtual image
3C150103Q015Eng
Two plane mirrors can be used to build a tool that enables one to see over obstacles. The tool is called
_______________ .
[Ans]
periscope
3C150103Q016Eng
To save energy, a series of _______________ are used to direct sunlight into a building.
[Ans]
15.3
plane mirrors
Colour
3C150103Q017Eng
When a beam of white light passes through a triangular prism, it is separated into a range of colours. This
phenomenon is called (a)______________ of light. The band of coloured lights seen is called the
(b)______________ of light.
[Ans]
(a) dispersion
(b) colour spectrum
158
Question Bank (Ch. 15)
3C150103Q018Eng
Colour spectrum consists of seven colour lights: (a)__________ , (b)__________ , (c)__________ ,
(d)__________ , (e)__________ , (f)__________ and (g)__________ .
[Ans]
(a) red
(b) orange
(c) yellow
(d) green
(e) blue
(f) indigo
(g) violet
3C150103Q019Eng
While a circular disc with seven colour sectors (red, orange, yellow, green, blue, indigo and violet) is spun
quickly, it looks __________ in colour.
[Ans]
white
3C150103Q020Eng
When light rays enter water droplets in air, ______________ occurs. Rainbow is formed from this
phenomenon.
[Ans]
dispersion
3C150103Q021Eng
Primary colours of light are (a)__________ , (b)__________ and (c)__________ .
[Ans]
(a) red
(b) green (c) blue
3C150103Q022Eng
Yellow, cyan and magenta are colours mixed from primary colours. They are called ______________
colours.
[Ans]
secondary
3C150203Q023Eng
Complete the following with a coloured light.
(a)
red light + blue light = ____________
(b)
red light +
(c)
magenta light +
[Ans]
___________
(a) magenta
light =
light
white light
____________ light = white light
(b) cyan
(c) green
3C150103Q024Eng
The surface of a colour television screen is coated with (a)____________ stripes. When these stripes are hit
by (b)____________ , they emit red, green and (c)____________ light.
[Ans]
(a) phosphor
(b) electron beams
(c) blue
3C150103Q025Eng
A colour filter only allows certain colour(s) of light to pass through. The light of other colours will be
(a)___________ . For example, a red apple will look (b)___________ when observed with a green filter.
[Ans]
(a) absorbed
(b) black
3C150103Q026Eng
Paper in ____________ colour will appear red under a yellow filter.
[Ans]
magenta
3C150103Q027Eng
A red apple appears red under white light because it _____________ red light.
[Ans]
reflects
3C150103Q028Eng
If an object absorbs all lights falling on it, the object will be ____________ in colour.
[Ans]
black
3C150103Q029Eng
If people have difficulties in distinguishing certain colours, they suffer from (a)________________ . It
happens when some (b)___________ in the retina do not function properly.
[Ans]
(a) colour blindness
(b) cones
3C150103Q030Eng
Colour blindness cannot be cured. It is caused by (a)_____________________ and it can be tested by
(b)_____________________________ .
[Ans]
(a) heredity (b) colour-blind test charts
159
Question Bank (Ch. 15)
3C150103Q031Eng
The most common kind of colour blindness is (a)____________ colour blindness. People having total colour
blindness will see everything that appears (b)_______________ , (c)_______________ and
(d)_______________ only.
[Ans]
(a) red-green
(b) black
(c) grey (d) white
15.4 Beyond the Visible Spectrum
3C150103Q032Eng
_____________________ is a radiation immediately beyond the red end of the visible spectrum. We can
make use of this radiation to measure body temperature.
[Ans]
Infrared radiation
3C150103Q033Eng
____________________ is a radiation immediately beyond the violet end of the visible spectrum. Fluorescent
materials will glow after they absorb this radiation.
[Ans]
Ultraviolet radiation
3C150103Q034Eng
The Sun emits different types of radiation. We will feel warm after absorbing (a)________________ and our
skin will become dark after absorbing (b)________________ .
[Ans]
(a) infrared radiation
(b) ultraviolet radiation
3C150103Q035Eng
(extension) Our skin absorbs ultraviolet radiation in sunlight and produces (a)_________________ .
Excessive exposure to ultraviolet radiation may cause (b)_________________ and (c)__________________ .
[Ans]
(a) vitamin D
(b) skin cancer
(c) cataracts
3C150103Q036Eng
(extension) CFCs in foaming agents and refrigerants react with ozone molecules and damage the
__________________ .
[Ans]
ozone layer
15.5 Beyond Infrared and Ultraviolet Radiations
3C150103Q037Eng
Among all electromagnetic waves, (a)___________ have the highest frequency and carry the largest amount
of energy. It can be used in hospitals to treat certain kinds of (b)_______________ .
[Ans]
(a) gamma rays
(b) cancer
3C150103Q038Eng
Among all electromagnetic waves, ___________________ have the lowest frequency. They are usually used
for broadcasting and communication.
[Ans]
radio waves
3C150103Q039Eng
The frequency of ___________________ is between radio waves and infrared. This radiation can be used to
cook and for communication.
[Ans]
microwaves
3C150103Q040Eng
When fast-moving electrons strike a heavy metal target, (a)_____________ are produced. The frequency of
this type of radiation is between (b)_______________ and (c)_______________ .
[Ans]
(a) X-rays
(b) ultraviolet
(c) gamma rays
3C150103Q041Eng
(a)_____________ are a type of radiation that has high penetrating power and can be used to check
(b)_____________________ (for security purposes) and (c)_____________________ (for medical purposes).
[Ans]
(a) X-rays
(b) luggage
(c) body tissues / bone fractures / joints / teeth
3C150103Q042Eng
(a)______________ can be absorbed by food and make the water molecules in the food (b)____________
vigorously. The food is thus heated up.
[Ans]
(a) Microwaves
(b) vibrate
160
Question Bank (Ch. 15)
3C150103Q043Eng
The working of some communication applications and radar relies on the ___________________ of
electromagnetic waves at the atmosphere and surface of objects.
[Ans]
reflection
3C150103Q044Eng
(extension) (a)__________________ from a mobile phone can interfere with medical equipment in hospitals.
It may also interfere with air navigation and (b)________________ equipment on aeroplanes.
[Ans]
15.6
(a) Radio waves
(b) communication
Refraction and Its Practical Uses
3C150103Q045Eng
(extension) As light travels from air into glass at an angle, it changes its (a)______________ at the boundary
between the two media. This phenomenon is called (b)__________________ . The refracted ray bends
(c)________________ (towards / away from) the normal.
[Ans]
(a) direction (b) refraction
(c) towards
3C150103Q046Eng
(extension) The depth of an object in water as observed is called (a)___________________ . It is
(b)__________________ (greater / less) then the actual depth and it is due to the (c)__________________ of
light.
[Ans]
(a) apparent depth (b) less
(c) refraction
3C150103Q047Eng
(extension) The middle part of a (a)____________ lens is thicker than the edge. When parallel light rays pass
through the lens from one side, they (b)____________ to a point on the other side.
[Ans]
(a) convex
(b) converge
3C150103Q048Eng
(extension) Place an object in front of a convex lens and an image is projected on a screen. No matter whether
the image is magnified or diminished, it is __________________ (erect/inverted).
[Ans]
inverted
3C150103Q049Eng
(extension) When a convex lens is used as a magnifying glass, the image formed is __________________
(erect/inverted).
[Ans]
erect
3C150103Q050Eng
(extension) Magnification of a convex lens is the ratio of the (a)_____________ size to the
(b)_____________ size.
[Ans]
(a) image
(b) object
3C150103Q051Eng
(extension) Build a telescope with two pieces of convex lens. The images formed are (a)______________
(magnified/diminished) and (b)_____________ (erect/inverted).
[Ans]
(a) magnified
(b) inverted
3C150103Q052Eng
(extension) In a microscope, the lens that is close to the object is called the (a)___________ and the lens
which is close to the eye is called the (b)____________ .
[Ans]
(a) objective
(b) eyepiece
3C150103Q053Eng
(extension) Build a microscope with two pieces of convex lens. The image formed by a microscope is
(a)____________ and (b)_____________ .
[Ans]
(a) inverted
(b) magnified
3C150203Q054Eng
(extension) The image of the letter “p” formed by a microscope should be ______ (b / q / d / p).
[Ans]
d
161
Question Bank (Ch. 15)
15.7
Optical Fibres and Total Internal Reflection
3C150103Q055Eng
(extension) When light rays enter air from glass, if the angle of (a)____________________ is greater than the
critical angle, (b)____________________ occurs.
[Ans]
(a) incidence
(b) total internal reflection
3C150103Q056Eng
(extension) Optical fibres make use of ___________________________ of light to transmit light and signals.
[Ans]
total internal reflection
3C150203Q057Eng
(extension) Mirage is due to the ___________________ reflection in air.
[Ans]
total internal
3C150103Q058Eng
(extension) A right-angled ______________ can turn light rays by 90 and 180.
[Ans]
prism
3C150103Q059Eng
(extension) Both (a)_____________________ and (b)______________________ can be used to make
periscopes.
[Ans]
(a) plane mirrors
(b) right-angled prisms
3C150103Q060Eng
(extension) An _____________________ is a medical application of optical fibre.
[Ans]
Endoscope
Short Questions
15.1
How We See an Object & 15.2 Reflection at Plane Surfaces
3C150204Q001Eng
A detective follows a suspect to a corner. He uses a small plane mirror to observe his target as shown below.
suspect
mirror
detective
(a)
What is the main characteristic of the paths of light?
__________________________________________________________________________
(b)
Draw light rays on the above diagram to show how the detective ‘sees’ the suspect.
(c)
The detective then holds back his mirror. Can the suspect see him at his current position? Explain your
answer by drawing suitable light rays on the above diagram.
__________________________________________________________________________
[Ans]
(a)
The paths of light are straight lines.
(b)
(c)
No.
162
Question Bank (Ch. 15)
3C150104Q002Eng
A sorcerer stands in front of a mirror and brings life to his mirror image.
He asks his image, ‘You must hold your magic stick with your right hand like I do. Why are you using your
left hand?’
His image replies, ‘Is there anything wrong with your eyes? I am using my right hand!’
Which of them is having a problem? Explain briefly.
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
[Ans]
Both of them are fine and are telling what they see honestly. The sorcerer sees his image holding the stick
with his left hand because the image formed by a mirror is laterally inverted.
3C150204Q003Eng
A light ray is directed onto a plane mirror which is just in front of some wooden stairs as shown below.
20 cm
(a)
Determine the angle of incidence and angle of reflection.
__________________________________________________________________________
(b)
Can the reflected ray pass over the first stair? If it can, can it pass over the second? If it can’t, where
will it hit the first stair?
__________________________________________________________________________
[Ans]
(a)
angle of incidence = 30o/ angle of reflection = 30o
(b)
It can’t. It will hit the first stair 11.5 cm above the mirror.
3C150104Q004Eng
Drivers must use mirrors properly when they drive. The photo shown below is the image in the rear-view
mirror of a car.
(a)
What is the use of the rear-view mirror? How does the driver see the vehicles behind him using the
mirror?
__________________________________________________________________________
__________________________________________________________________________
(b)
In the above photo, can you read the manufacturer of the van correctly?
__________________________________________________________________________
[Ans]
(a)
To see the cars and other events behind the driver.
Light is reflected by the vehicles and then by the mirror and enters the driver’s eyes.
(b)
The van should be TOYOTA.
163
Question Bank (Ch. 15)
3C150104Q005Eng
Some old buses are still equipped with periscopes that enable the driver to see the upper deck. Newer buses
usually have video cameras to perform this function.
(a)
Draw mirrors and a suitable light ray on the above diagram to show how a periscope works in a bus.
(b)
The bus driver can see the upper deck through the periscope. Conversely, can we see the driver if we
look into the periscope on the upper deck? Draw another light ray to explain your answer.
(c)
Name another situation where a periscope is used.
__________________________________________________________________________
[Ans]
(a)
(b)
Yes
(c)
Submarines
3C150104Q006Eng
The figure below shows a small object which is placed in front of a plane mirror.
(a)
Draw a pair of light rays to locate the image of the object. Which TWO properties about an image
formed by a plane mirror can you deduce from your drawing?
__________________________________________________________________________
(b)
State TWO other properties of an image formed by a plane mirror.
__________________________________________________________________________
164
Question Bank (Ch. 15)
[Ans]
(a)
Virtual / Same distance away from mirror
(b)
Same size of the object / upright / laterally inverted (any two of them)
3C150204Q007Eng
(a)
State the laws of reflection on a plane mirror.
__________________________________________________________________________
(b)
The diagrams shown below are two plane mirrors at right angles to each other. Two light rays are
directed onto one of the mirrors at different angles. Complete the ray diagrams.
(c)
What do you discover about the directions of the incident ray and the final reflected ray?
__________________________________________________________________________
[Ans]
(a)
Angle of incidence = angle of reflection / The incident ray and reflected ray lie in the same plane.
(b)
(c)
15.3
The final reflected ray is always parallel to the incident ray.
Colour
3C150104Q008Eng
When a beam of white light is directed onto a prism, it spreads out into different colours.
white light
(a)
What is this phenomenon called?
__________________________________________________________________________
(b)
What can you conclude about the nature of white light from this experiment?
__________________________________________________________________________
(c)
Write down the colours of the spectrum formed in sequence.
__________________________________________________________________________
[Ans]
(a)
The dispersion of white light
(b)
White light is a mixture of lights of different colours.
(c)
Red / Orange / Yellow / Green / Blue / Indigo / Violet
165
Question Bank (Ch. 15)
3C150104Q009Eng
(a)
Briefly describe how a rainbow is formed in the sky. (Diagrams NOT required.)
__________________________________________________________________________
__________________________________________________________________________
(b)
Hence, explain why rainbows usually form after rain or when the air is humid. Do you think you will
see rainbows frequently in dry weather?
__________________________________________________________________________
__________________________________________________________________________
[Ans]
(a)
Water droplets in the air are like little prisms in the sky. When sunlight passes through these droplets,
it spreads out into a spectrum of different colours and forms the rainbow we see.
(b)
This is because the formation of rainbows requires water droplets. There are more droplets in the air
after rain or in humid weather and the rainbow formed is easier to be seen.
No.
3C150204Q010Eng
The table below contains some information about the colours of three objects. Fill in the remaining blanks.
Apparent colour of the object
Light shone
on the object
A
B
White
White
Green
Yellow
Yellow
Blue
(c)
C
(a)
(b)
Green
(d)
Black
[Ans]
(a)
Green
(b)
Green
(c)
Blue
(d)
Black
3C150104Q011Eng
(a)
A colour chart is shown below. It shows how the primary colours P, Q and R can be mixed to give
secondary colours Z, cyan and magenta.
(i)
Identify the colours P, Q, R and Z.
____________________________________________________________________
(ii)
The colour W at the centre is obtained by mixing all the three primary colours in appropriate
amounts. What is the colour W?
____________________________________________________________________
(b)
A lemon appears yellow when it is illuminated by white light.
(i)
What primary colour(s) does it absorb and what primary colour(s) does it reflect?
____________________________________________________________________
(ii)
What will be its apparent colour when it is illuminated by blue light? Explain your answer.
____________________________________________________________________
[Ans]
(a)
(i) P = red / Q = green / R = blue / Z = yellow
(ii) W = white
(b)
(i) It absorbs blue and reflects red and green.
(ii) When white light shines on the lemon, it appears yellow. This shows that it absorbs blue light and
reflects red and green light. When blue light shines on it, the light will be absorbed and the lemon will
appear black.
166
Question Bank (Ch. 15)
3C150204Q012Eng
The screen of a television or a computer monitor contains a huge number of colour units. These units could be
phosphorous cells in CRT monitors or LCD cells in LCD monitors. In general, each of the units contains three
stripes that can emit red, green and blue lights respectively.
(a)
Briefly explain how the colour units produce specific colours that we see.
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
(b)
The left figure below shows the structure of a colour unit on a TV screen. The right figure shows a
letter displayed on the screen. What is this letter? What are its colour and the colour of the background
respectively?
__________________________________________________________________________
[Ans]
(a)
Each unit contains stripes that can emit light of the three primary colours. Each unit therefore produces
different colours by adjusting the brightness of the three stripes, and the whole image is formed on the
screen with an appropriate combination of the colours from these units.
(b)
E
Letter = yellow; Background = black
3C150104Q013Eng
A wall is originally blue in colour under white light.
(a)
Explain why the wall appears blue in terms of the absorption and reflection of colours.
__________________________________________________________________________
__________________________________________________________________________
(b)
A worker paints the wall yellow. What can you say about the absorption and reflection of colours of
this yellow paint?
__________________________________________________________________________
__________________________________________________________________________
(c)
The worker then paints the wall black. What can you say about the absorption and reflection of colours
of the black paint?
__________________________________________________________________________
__________________________________________________________________________
[Ans]
(a)
Since the wall reflects blue light and absorbs all the other colours in white light, it appears blue.
(b)
The yellow paint reflects yellow light and absorbs all the other colours in white light.
(c)
The black paint absorbs all the colours in white light.
167
Question Bank (Ch. 15)
3C150204Q014Eng
A yellow dot is drawn on a piece of black paper. A student observes this yellow dot through a red filter and a
blue filter.
Three parallel rays of the primary colours are drawn on the diagram.
(a)
How many primary colours are there? What are they?
__________________________________________________________________________
(b)
Extend the light rays to show how the yellow dot is seen by the student.
(c)
What is the apparent colour of the dot as seen by the student?
__________________________________________________________________________
[Ans]
(a)
Three
Red, green and blue
(b)
(c)
Red
3C150204Q015Eng
Three objects X, Y and Z are shown below. When they are illuminated by white light, X appears blue, Y is
transparent and Z appears black. The figures include three light rays of the primary colours and an eye for
each of the objects. Extend the light rays to show how they are reflected, transmitted and absorbed by the
objects.
[Ans]
168
Question Bank (Ch. 15)
15.4 Beyond the Visible Spectrum
3C150104Q016Eng
The photo below is the signal emitter of a television remote control.
(a)
What kind of electromagnetic radiation is used to transmit the signals?
__________________________________________________________________________
(b)
How is the frequency of the radiation compared with that of visible light? Can we see it with our eyes?
__________________________________________________________________________
(c)
Suggest another use of this kind of radiation.
__________________________________________________________________________
[Ans]
(a)
Infrared radiation
(b)
The frequency of this radiation is lower than that of visible light.
No.
(c)
Infrared alarm sensors / infrared thermometers / infrared photography / infrared detectors (any one of
them)
3C150104Q017Eng
(extension) We know that colour filters only allow light of specific colours to pass through and block other
colours. Suntan lotion and sunglasses have similar filtering effects. They are used to protect us from a kind of
radiation in sunlight.
(a)
What is this radiation?
__________________________________________________________________________
(b)
How is its frequency compared with that of visible light? Can we see it with our eyes?
__________________________________________________________________________
(c)
What are the consequences of over-exposure to this radiation?
__________________________________________________________________________
[Ans]
(a)
Ultraviolet radiation
(b)
The frequency of this radiation is higher than that of visible light.
No.
(c)
Sunburn / Skin cancer / Cataracts
3C150104Q018Eng
Some materials emit visible light when they absorb ultraviolet radiation.
(a)
What is this phenomenon called?
__________________________________________________________________________
(b)
Some jellyfish contain this kind of material and will glow after absorbing sunlight.
(i)
Briefly describe how the jellyfish glows after absorbing sunlight.
____________________________________________________________________
(ii)
Name TWO other situations where you can find this kind of glowing material.
____________________________________________________________________
169
Question Bank (Ch. 15)
[Ans]
(a)
(b)
Fluorescence
(i) Sunlight contains ultraviolet radiation. The fluorescent material in the jellyfish emits visible light
after absorbing the ultraviolet radiation.
(ii) Fireman gown / Zebra crossing
3C150104Q019Eng
Suppose you are given a fluorescent material and you want to make a fluorescent mark ‘IS’ which glows
under an ultraviolet lamp.
(a)
On the paper shown above, in which area will you paint the fluorescent material, A or B?
__________________________________________________________________________
(b)
Explain how the mark ‘IS’ glows under an ultraviolet lamp.
__________________________________________________________________________
__________________________________________________________________________
(c)
State a daily application of this technique.
__________________________________________________________________________
[Ans]
(a)
(b)
B
Only region B is painted with a fluorescent material. When the paper is put under an ultraviolet lamp,
the material absorbs ultraviolet radiation and then emits visible light. The mark ‘IS’ therefore glows.
(c)
Checking fake bank notes and other documents.
15.5 Beyond Infrared and Ultraviolet Radiations
3C150104Q020Eng
(a)
The light that we can see belongs to a special range of frequencies in the electromagnetic spectrum.
Different colours are in fact radiations of different frequencies. The visible spectrum can be roughly
divided into 7 colours. State these 7 colours and arrange them in the order of increasing frequencies.
__________________________________________________________________________
(b)
Visible light only forms a small part of the electromagnetic spectrum.
(i)
Fill in the blanks in the spectrum with appropriate types of radiation.
____________________________________________________________________
(ii)
State ONE application for each of the types except visible light.
____________________________________________________________________
[Ans]
(a)
(b)
Red < orange < yellow < green < blue < indigo < violet
(i) Radio waves / infrared radiation / ultraviolet radiation / gamma rays
(ii) Radio waves: signal transmission in radios / televisions / mobile phones / wireless computer
networks (any one of them)
Infrared radiation: infrared alarm sensors / infrared thermometers / infrared photography / infrared
detectors / infrared remote controls (any one of them)
Ultraviolet radiation: check fake bank notes / sterilisation (any one of them)
Gamma rays: cancer treatment / sterilisation (any one of them)
170
Question Bank (Ch. 15)
3C150204Q021Eng
The figure below compares the visible range of a human and that of a certain bee in the electromagnetic
spectrum.
(a)
What colours have the lowest frequency and the highest frequency respectively in the human visible
range?
__________________________________________________________________________
(b)
There is a range that the bee can see while a human cannot. What kind of radiation is this?
__________________________________________________________________________
(c)
Now there is a flower which appears red in the human eye. Do you think the bee will see it as a red
flower as well? Why?
__________________________________________________________________________
[Ans]
(a)
Lowest: red; highest: violet
(b)
Ultraviolet radiation
(c)
No, because the bee cannot see red colour.
3C150104Q022Eng
High definition (HD) TV signals are emitted from a number of transmitters in Hong Kong. They are located at
various places like Temple Hill, Kowloon Peak, Castle Peak and Lamma Island etc.
(a)
What kind of electromagnetic radiation is used in transmitting TV signals?
__________________________________________________________________________
(b)
How does Cable TV transmit TV signals? What is their difference from the free TV providers?
__________________________________________________________________________
(c)
Suggest TWO other applications of the radiation you named in (a).
__________________________________________________________________________
[Ans]
(a)
(b)
Radio waves
Cable TV transmits signals using underground cables (optical fibres). Free TV providers transmit
signals by radio waves in the air.
(c)
Radios / mobile phones / wireless computer networks (any two of them)
3C150104Q023Eng
Lasers are strong, highly focused light beams. They have many applications, from entertainment to medical
and industrial uses.
(a)
Compare a red laser beam and a blue laser beam. Which beam is more energetic? Why?
__________________________________________________________________________
(b)
Industrial lasers are so strong that they can be used to cut materials and even as scalpels in surgeries.
Can you explain how lasers cut materials?
__________________________________________________________________________
__________________________________________________________________________
[Ans]
(a)
Blue laser has a higher frequency, hence more energetic.
(b)
The high energy of the laser produces heat and melts the material at the place the laser hits.
15.6
Refraction and Its Practical Uses
3C150104Q024Eng
(extension) The following figure shows that a light ray bends when it travels from a medium A to a medium
B.
(a)
What is this phenomenon called?
__________________________________________________________________________
(b)
What are the angles θ and  called?
__________________________________________________________________________
171
Question Bank (Ch. 15)
(c)
Which medium, A or B, has a higher density? Why?
__________________________________________________________________________
[Ans]
(a)
Refraction
(b)
θ = angle of incidence ;  = angle of refraction
(c)
B has a higher density because the refracted ray is bent towards the normal.
3C150204Q025Eng
(extension) A set of parallel light rays are directed onto a convex lens.
(a)
(i)
(ii)
Extend the rays to show how they travel after passing through the lens.
Describe a simple set-up to demonstrate the result in (i).
____________________________________________________________________
____________________________________________________________________
(b)
Putting a magnifying glass under sunlight for a long time could be dangerous. Why?
__________________________________________________________________________
__________________________________________________________________________
[Ans]
(a)
(i)
(ii) Put a ray box and a convex lens on a piece of paper. Use a sieve to produce a set of parallel light
rays from the ray box. Direct the light rays onto the lens and observe how the light rays pass through
the lens.
(b)
A magnifying glass is a convex lens. Sunlight will converge to a point after passing through the lens.
The energy from the light will be focused and cause the things under the glass to burn.
3C150104Q026Eng
(extension)
(a)
Is the image formed by a convex lens always magnified?
__________________________________________________________________________
(b)
If the object is placed very close to a convex lens, will the image be magnified or diminished?
__________________________________________________________________________
(c)
Hence, state an application of convex lenses under such a situation.
__________________________________________________________________________
(d)
A convex lens is placed in front of an object of height 1.2 cm. If the height of the image formed is 1.8
cm, what is its magnification?
__________________________________________________________________________
[Ans]
(a)
No. The image size depends on the distance between the lens and the object.
(b)
Magnified
(c)
Magnifying glass
(d)
1.5
172
Question Bank (Ch. 15)
3C150204Q027Eng
(extension) A glass block is placed on top of a book. The words on the book appear to be raised as shown
below.
The following figure shows the ray diagram of the above situation.
(a)
Explain why the light rays bend away from the normal when they leave the glass block and enter the
air. What is this phenomenon called?
__________________________________________________________________________
__________________________________________________________________________
(b)
What is the angle of incidence and angle of refraction of the light rays?
__________________________________________________________________________
(c)
Using the information shown in the diagram, find the apparent height of the words above the book.
__________________________________________________________________________
[Ans]
(a)
Since the glass block is denser than air, light rays bend away from the normal when they leave the
glass and enters the air due to refraction.
(b)
Angle of incidence = 30o / angle of refraction = 60o
(c)
2.11 cm
15.7
Optical Fibres and Total Internal Reflection
3C150104Q028Eng
(extension) Two scientists Ben and Grace are trying to ‘bend’ light rays using plane mirrors. They first build a
‘channel’ for the light to travel using walls with a series of corners as shown. Ben then stands at one end of
the ‘channel’ while Grace stands at the other end.
Grace
Ben
(a)
Draw mirrors and a suitable light ray to show how Grace can see Ben and say hi to him.
(b)
Can Grace see Ben directly without the mirrors? Why?
__________________________________________________________________________
__________________________________________________________________________
(c)
Name ONE technology that applies total internal reflections to achieve an effect similar to this
example.
__________________________________________________________________________
173
Question Bank (Ch. 15)
[Ans]
(a)
(b)
No, because the light from Fai is blocked by the walls.
(c)
Optical fibre
3C150104Q029Eng
(extension)
(a)
An optical fibre transmits signals by light. What phenomenon does it apply in doing so?
__________________________________________________________________________
(b)
Draw a diagram to show how an optical fibre works.
(c)
Optical fibres are heavily used in telecommunication. During the Hengchun earthquake in 2006,
several major undersea cables of optical fibres were damaged, causing serious an internet and phone
failure in Hong Kong. State THREE advantages of optical fibres over copper wires for transmitting
signals.
__________________________________________________________________________
__________________________________________________________________________
[Ans]
(a)
Total internal reflection
(b)
(c)
Less signal loss / less interference / lighter / corrosion free / less expensive / higher capacity (any three
of them)
3C150104Q030Eng
(extension) A light ray is directed from a medium X to a medium Y. It hits the boundary between the two
media at a point O as shown.
(a)
State TWO conditions for total internal reflection to occur at O.
__________________________________________________________________________
__________________________________________________________________________
174
Question Bank (Ch. 15)
(b)
Given that in the above situation, total internal reflection will occur when the angle of incidence is
greater than 42o. Draw the subsequent light ray on the diagram.
[Ans]
(a)
 Medium X has a higher density than medium Y.
 The angle of incidence is greater than a certain value.
(b)
Long Questions
15.1
How We See an Object
3C150105Q001Eng
Two photos of the same room are shown below. All the lights in the room are switched off in the left photo.
Room with all the lights switched off
(a)
Room with all the lights switched on
Explain the difference between a luminous object and a non-luminous object.
__________________________________________________________________________
__________________________________________________________________________
(b)
Why can’t we see both luminous and non-luminous objects when the lights are switched off?
__________________________________________________________________________
(c)
Why can we see both luminous and non-luminous objects when the lights are switched on?
__________________________________________________________________________
[Ans]
(a)
A luminous object emits light itself.
A non-luminous object doesn’t emit light but can be seen when it reflects light.
(b)
Luminous objects do not emit light. No light is reflected by non-luminous objects.
(c)
Luminous objects emit light. Non-luminous objects reflect light from luminous objects.
3C150205Q002Eng
A rod of length 2 m stands vertically on the floor in a room. A light bulb is hung on the ceiling at a height of
3 m at the position shown below. When the bulb is switched on, a shadow of the rod is cast on the floor.
(a)
How does the shadow form?
__________________________________________________________________________
(b)
Draw suitable light rays in the above diagram to find the length of the shadow.
(c)
If the bulb is lowered to 2.5 m above the floor, how will the length of the shadow change?
__________________________________________________________________________
[Ans]
(a)
The rod blocks the light from the bulb and the light cannot reach the floor.
175
Question Bank (Ch. 15)
(b)
Length = 4 m
(c)
The length of the shadow increases.
3C150205Q003Eng
(a)
Explain the difference in the light that comes from the Sun and the Moon.
__________________________________________________________________________
(b)
You may have heard of events like solar eclipse and lunar eclipse.
(i)
Solar eclipse happens when the Moon moves to the position between the Earth and the Sun, and
the Sun, the Earth and the Moon lie on a straight line. Explain why the Sun appears dark in a
solar eclipse.
____________________________________________________________________
____________________________________________________________________
(ii)
Draw the positions of the Sun, the Earth and the Moon during a lunar eclipse and explain why
the Moon appears dark in such an event.
____________________________________________________________________
____________________________________________________________________
[Ans]
(a)
(b)
The Sun emits light itself. The Moon reflects light from the Sun.
(i) The Moon blocks the light from the Sun and the light cannot reach the Earth. So observers on the
Earth see the Sun as black.
(ii) The Earth blocks the light from the Sun. The light cannot reach the Moon. The Moon does not
reflect light back to the Earth and hence appears black.
15.2
Reflection at Plane Surfaces
3C150105Q004Eng
(a)
State the TWO laws of reflection of light on a plane mirror.
__________________________________________________________________________
__________________________________________________________________________
(b)
One of the uses of mirrors in interior design is to produce a feeling of spaciousness. The photo below
shows the reception hall of a restaurant. One side of the hall is covered with a panel of mirrors. Explain
why the hall would look twice as large as its original size.
__________________________________________________________________________
__________________________________________________________________________
(c)
State another use of mirrors in the design of a building.
__________________________________________________________________________
176
Question Bank (Ch. 15)
(d)
The overuse of mirrors in an indoor environment may lead to an unpleasant heating effect. Why?
__________________________________________________________________________
__________________________________________________________________________
[Ans]
(a)
Angle of incidence = angle of reflection
The incident ray and the reflected ray lie in the same plane.
(b)
The image formed by a plane mirror will at the same distance behind the mirror as the object is. So the
opposite wall of the hall will have an image at a distance equal to the original size of the hall behind
the mirror, and the hall will look twice as large.
(c)
Provide natural lighting
(d)
Because light reflected by the mirrors will be trapped in the room and cause the temperature to rise.
3C150105Q005Eng
(a)
The two diagrams below show an identical set of parallel light rays being directed onto a plane mirror
and a rough surface respectively.
(i)
Draw the reflected rays according to the laws of reflection.
(ii)
You should see that the light rays do not reflect in the same way in the two cases. What are
these two kinds of reflection called?
____________________________________________________________________
(b)
When we stand in front of a mirror, we see a clear image of ourselves. But do not see such an image
when we stand in front of a wall. Is it because the mirror reflects light while the wall does not? If not,
what is the true reason?
__________________________________________________________________________
__________________________________________________________________________
(c)
Here we see a nice photo of the Taj Mahal in India. A perfect reflection is formed on the pond in front
of the building.
(i)
What is the condition of the water surface for such a clear image to form?
____________________________________________________________________
(ii)
Do you expect to see that image again on a windy day? Why?
____________________________________________________________________
[Ans]
(a)
(i)
(ii) Regular reflection and diffuse reflection
(b)
No, the wall does reflect light. But since the wall is not smooth, the light will undergo diffuse
reflection and we cannot see a clear image of ourselves.
(c)
(i) The water must be clear and calm to form a flat surface.
(ii) No, because there will be ripples on the water surface and this leads to diffuse reflection.
177
Question Bank (Ch. 15)
15.3
Colour
3C150105Q006Eng
How do traffic lights produce light of different colours? New traffic lights contain modern LEDs which
produce red, yellow and green light respectively. But old traffic lights are equipped with normal white light
bulbs. They produce different colours using filters on the lids.
(a)
(i)
Distinguish the two types of colours: primary colours and secondary colours.
____________________________________________________________________
____________________________________________________________________
(ii)
Among the three colours in a traffic light, two of them are primary colours. What are they?
____________________________________________________________________
(iii)
How can we obtain the remaining secondary colour from the primary colours?
____________________________________________________________________
(b)
In an old traffic light, the red light is produced by white light passing through a red filter.
(i)
What is white light?
____________________________________________________________________
(ii)
How does the red filter produce red light from white light?
____________________________________________________________________
(iii)
If we direct white light through a red filter and then through a green filter, what colour will we
get? Why?
____________________________________________________________________
____________________________________________________________________
[Ans]
(a)
(i) Primary colours are the basis of all colours. Secondary colours are colours that can be produced by
mixing the primary colours with appropriate proportions.
(ii) Red and green
(iii) Mixing red and green will give yellow.
(b)
(i) White light is the mixture of all colours.
(ii) The red filter only allows the red colour to pass through when white light is directed onto it.
(iii) No light will emerge out of the green filter because only red light can pass through the red filter,
and the green filter blocks it subsequently.
3C150205Q007Eng
(a)
There are two types of light sensitive cells on the retina of the human eye.
(i)
What are they called?
____________________________________________________________________
(ii)
Which type is responsible for colour vision?
____________________________________________________________________
(b)
(i)
How many types of colour sensitive cells are there on the retina?
____________________________________________________________________
(ii)
What colours do the colour sensitive cells detect?
____________________________________________________________________
(c)
(i)
What is colour blindness? What is its cause?
____________________________________________________________________
(ii)
Can you describe an example of colour blindness?
____________________________________________________________________
[Ans]
(a)
(i) Rods and cones
(ii) Cone cells are responsible for colour vision.
(b)
(i) Three
(ii) Red, green and blue
(c)
(i) Colour blindness is the inability to distinguish certain colours. It happens when some cones in the
retina do not function properly.
(ii) A person with red-green colour blindness cannot distinguish between red and green.
178
Question Bank (Ch. 15)
15.4 Beyond the Visible Spectrum
3C150105Q008Eng
There is an infrared imaging system at the Airport. The image is taken by an infrared camera.
(a)
How is the frequency of infrared radiation compared with that of visible light?
__________________________________________________________________________
(b)
How does the amount of infrared radiation emitted by a body depend on its temperature?
__________________________________________________________________________
(c)
In an infrared image, the body of the visitor has regions of different colours. What do the colours
represent?
__________________________________________________________________________
(d)
The imaging system was installed at the Airport after the SARS incident in 2003 to spot out visitors
who have abnormal body temperature. How does the system achieve this purpose?
__________________________________________________________________________
__________________________________________________________________________
[Ans]
(a)
Infrared radiation has a lower frequency than visible light.
(b)
The higher the body temperature, the more infrared radiation it emits.
(c)
The colours represent different temperature ranges.
(d)
Immigration officers inspect the body temperature of the visitors by observing the colours displayed on
the infrared image. Anyone with abnormal body temperature will be spotted as abnormal colours in the
image.
3C150105Q009Eng
(extension) Over-exposure to sunlight may lead to sunburn and even skin cancer in serious cases. People with
light skin colour are generally more prone to sunburn because the dark pigments in our skin help to protect us
against strong radiations from the Sun.
(a)
(i)
What kind of radiation in sunlight is responsible for causing skin cancer? What is its
abbreviation?
____________________________________________________________________
(ii)
How is the frequency of this radiation compared with that of visible light?
____________________________________________________________________
(iii)
Can we see this radiation with our eyes? Why?
____________________________________________________________________
(b)
There is a layer in the Earth’s atmosphere that gives us important protection against this radiation.
(i)
What is this layer?
____________________________________________________________________
(ii)
It was found in the 1970s that this protective layer was getting thinner. The cause could be the
release of certain chemicals. Name ONE example of these chemicals. Where is it used?
____________________________________________________________________
(c)
Suggest TWO other ways that we can protect ourselves from the radiation discussed above.
__________________________________________________________________________
[Ans]
(a)
(i) Ultraviolet radiation; UV
(ii) Its frequency is higher than that of visible light.
(iii) No, because it is beyond the visible spectrum.
(b)
(i) Ozone layer
(ii) CFCs
In sprays, refrigerants, foaming agents and cleaning fluids (any one of them)
(c)
Wearing sunglasses and long-sleeved clothes
179
Question Bank (Ch. 15)
15.5 Beyond Infrared and Ultraviolet Radiations
3C150105Q010Eng
X-rays and gamma rays are electromagnetic radiation of the highest frequency.
(a)
(i)
Which of them has a higher frequency?
____________________________________________________________________
(ii)
Which of them is more energetic and penetrating?
____________________________________________________________________
(b)
X-rays are used in medical imaging. The X-ray image of the chest of a man is shown below. The white
regions are mostly bones.
(i)
Explain how such an image is produced.
____________________________________________________________________
____________________________________________________________________
(ii)
State another application of X-rays.
____________________________________________________________________
(c)
Gamma rays are also used in medicine.
(i)
What are their uses in this field? Why are they used this way?
____________________________________________________________________
____________________________________________________________________
(ii)
Unlike X-rays, gamma rays are seldom used in medical imaging. Suggest TWO reasons.
____________________________________________________________________
____________________________________________________________________
[Ans]
(a)
(i) Gamma rays
(ii) Gamma rays
(b)
(i) When X-rays are directed onto the body of the man, they pass through the flesh readily but not the
bones. This results in bright and dark regions in the image as shown above.
(ii) Checking airport luggage.
(c)
(i) Cancer treatment and sterilisation. Because they are highly energetic and penetrating.
(ii) They carry so much energy that they may be harmful to the patients. They are so penetrating that
they will pass through both the bones and the flesh when taking images.
3C150105Q011Eng
(extension)
(a)
(i)
What kind of electromagnetic radiation is used in mobile phones to transmit signals?
____________________________________________________________________
(ii)
When is this radiation the strongest?
____________________________________________________________________
(b)
Suggest TWO other situations where this radiation is used to transmit signals.
__________________________________________________________________________
(c)
Describe a simple demonstration to show that the radiation emitted by a mobile phone has a magnetic
effect.
__________________________________________________________________________
180
Question Bank (Ch. 15)
(d)
(i)
We must switch off our mobile phones when we are in a hospital. One reason is to avoid
disturbances to the patients. Suggest another reason.
____________________________________________________________________
(ii)
Name another situation where the same rule is enforced.
____________________________________________________________________
[Ans]
(a)
(i) Radio waves
(ii) When you dial, receive a call or send a message.
(b)
Radios / televisions / wireless computer networks (any two of them)
(c)
Put a mobile phone near a compass. Make a call and see how the needle of the compass moves.
(d)
(i) The radio waves will interfere with the medical instruments.
(ii) On aeroplanes during take-off and landing
3C150205Q012Eng
‘Radar’ refers to a method of detection. It stands for RAdio Detection And Ranging. A radar system uses
electromagnetic radiation to carry out detection and obtain information such as the position, altitude and
speed of the target.
(a)
Suggest a kind of electromagnetic radiation that is often used in radar.
__________________________________________________________________________
(b)
Suggest TWO situations where a radar system is used.
__________________________________________________________________________
(c)
(i)
A radar system detects an approaching aeroplane. Briefly describe how the system carries out
the detection using electromagnetic radiation.
____________________________________________________________________
____________________________________________________________________
(ii)
Suppose the system uses the radiation you named in (a). A military engineer proposes a
counter-measure. He paints the aeroplane with a material that absorbs most of that radiation. Do
you think the radar system can still detect the plane?
____________________________________________________________________
(d)
The technique in (c)(i) is used with lasers in one of the operations of the police. What is this operation?
__________________________________________________________________________
[Ans]
(a)
Radio waves / microwaves (any one of them)
(b)
Ship navigation / airport control / military (any one of them)
(c)
(i) The transmitter of the radar system emits microwaves towards the target. The target then reflects the
microwaves back to the receiver. The reflected waves are then analysed to give information of the
target.
(ii) No, because the plane reflects the radiation back to the receiver.
(d)
15.6
Catching speeding cars
Refraction and Its Practical Uses
3C150105Q013Eng
(extension)
(a)
What is the refraction of light?
__________________________________________________________________________
__________________________________________________________________________
(b)
(i)
When a beam of white light is directed onto a prism as shown, what will happen? What is this
phenomenon called?
____________________________________________________________________
____________________________________________________________________
(ii)
What can you conclude about white light through this experiment?
____________________________________________________________________
181
Question Bank (Ch. 15)
(c)
In fact, lights of different colours are refracted by different extent by a prism. For example, red light is
bent by the least while violet is bent by the most. Using this information, can you explain the
phenomenon you described in (b)(i)?
[Ans]
(a)
Refraction is the change in direction of a light ray when it travels from one medium to another.
(b)
(i) The white light will be spread out into different colours. Dispersion.
(ii) White light is composed of different colours.
(c)
When white light enters the prism, red light will be bent least and violet light will be bent the most.
The colours therefore follow different paths in the prism and become separated when they emerge.
3C150205Q014Eng
(extension) A beam of white light is produced by a ray box and a convex lens. The beam passes through a
prism and is refracted onto a screen as shown.
(a)
(i)
What is the refraction of light?
____________________________________________________________________
(ii)
In the above process, where does refraction occur?
____________________________________________________________________
(b)
From the above diagram, what can you conclude about the relationship between the degree of bending
of light and its frequency?
__________________________________________________________________________
(c)
(i)
There is in fact radiation that reaches position A and position B respectively. What are these
radiations? What is your reasoning?
____________________________________________________________________
____________________________________________________________________
(ii)
Briefly describe a method to detect each of the radiations in (i) and show that your prediction
about their positions is correct.
____________________________________________________________________
____________________________________________________________________
[Ans]
(a)
(i) Refraction is the change in direction of a light ray when it travels from one medium to another.
(ii) At the convex lens and at the prism
(b)
(c)
The higher the frequency, the greater is the degree of bending.
(i) A has a higher frequency than violet light, so it is ultraviolet radiation.
B has a lower frequency than red light, so it is infrared radiation.
(ii) Use an infrared detector / thermometer to look for infrared signals at B. Stick a fluorescent tape on
the screen and look for fluorescence at A.
3C150205Q015Eng
(extension)
(a)
The depth of a swimming pool as seen by a swimmer at the pool side is always shallower than the real
depth.
(i)
Draw a ray diagram to show why.
____________________________________________________________________
182
Question Bank (Ch. 15)
(ii)
If the pool is filled with oil instead of water, do you think the apparent depth will change? Will
the apparent depth become deeper than the real depth? Why?
____________________________________________________________________
____________________________________________________________________
(b)
In the contrary, what will be seen by a diver under water? Consider a diver under water looking at a
bird above the pool side.
(i)
Draw a light ray on the diagram and roughly indicate the position of the image seen by the
diver.
(ii)
What is the difference in the apparent height of the bird as seen by the diver from the real
height?
____________________________________________________________________
[Ans]
(a)
(i)
Light rays from the bottom of the pool will refract when they leave the water surface. The image of the
bottom will therefore appear to be at a higher level as shown in the above ray diagram.
(ii) Yes, because water and oil bend light by different amounts. No, because oil is still denser than air.
(b)
(i)
(ii) The apparent height is greater than the real height.
3C150205Q016Eng
(extension)
(a)
What kind of lens is a magnifying glass?
__________________________________________________________________________
(b)
The diagram below shows an object which is placed very close to a magnifying glass. Several light
rays from the tip and bottom of the object have been drawn.
(i)
Locate the image of the object on the diagram.
(ii)
Is the image real or virtual? On which side of the glass is it located?
____________________________________________________________________
(iii)
Find the magnification of the image.
____________________________________________________________________
183
Question Bank (Ch. 15)
(c)
The glasses worn by a long-sighted person are in fact magnifying glasses too. If you look at the eyes of
such a person through his/her glasses, will the eyes appear to be larger or smaller than the actual size?
__________________________________________________________________________
[Ans]
(a)
Convex lens
(b)
(i)
(ii) Virtual. It is located on the side of the object.
(iii) 2
(c)
15.7
Larger
Optical Fibres and Total Internal Reflection
3C150205Q017Eng
(extension) A light ray travels from water to air. The following table shows the relationship between the angle
of incidence θi and the angle of refraction θr when the ray is refracted at the boundary.
(a)
θi
θr
5°
6.66°
15°
20.1°
30°
41.7°
45°
70.1°
Plot a graph of sin θi against sin θr. What do you conclude from your graph?
__________________________________________________________________________
(b)
(i)
Extend your graph to find the value of θi when θr becomes 90°. Draw a ray diagram to
demonstrate this situation.
____________________________________________________________________
(ii)
What happens when θi is larger the value in (i)? Draw another ray diagram to demonstrate this
situation.
____________________________________________________________________
(iii)
What is this phenomenon called?
____________________________________________________________________
[Ans]
(a)
sin θi is proportional to sin θr.
184
Question Bank (Ch. 15)
(b)
(i) 48° - 49°
(ii) The light ray will be reflected back into the water.
(iii) Total internal reflection
3C150205Q018Eng
(extension)
(a)
The diagram below shows the hand and the eye of a student. Add light rays to the diagram to show
how the student sees his hand.
(b)
(i)
What is the refraction of light?
____________________________________________________________________
(ii)
What is total internal reflection of light? When will it happen?
____________________________________________________________________
____________________________________________________________________
(c)
The student now puts a tank of water besides his hand as shown below. The tank is transparent. He
discovers that he cannot see his hand through the water. Explain this phenomenon by adding light rays
to the diagram.
__________________________________________________________________________
__________________________________________________________________________
[Ans]
(a)
(b)
(i) Refraction is the change in direction of a light ray when it travels from one medium to another.
(ii) Total internal reflection is the phenomenon that when a light ray travels from a denser medium to a
less dense medium, the ray will be reflected back at the boundary if the angle of incidence is greater
than a certain value.
185
Question Bank (Ch. 15)
(c)
The light reflected from the hand undergoes total internal reflection at the wall of the tank. The light
cannot reach the student’s eyes and therefore he cannot see his hands through the water.
3C150205Q019Eng
(extension) The figure below shows a straight optical fibre. The fibre consists of two layers of glass where the
outer layer has a lower density than the inner layer.
(a)
(i)
Briefly describe how an optical fibre transmits signals and explain why the density of the outer
layer of glass has to be lower.
____________________________________________________________________
____________________________________________________________________
____________________________________________________________________
(ii)
State TWO applications of optical fibres.
____________________________________________________________________
(iii)
State TWO advantages of optical fibres over copper wires in transmitting signals.
____________________________________________________________________
(b)
(i)
A light ray enters the fibre at an angle of 30° to the fibre as shown. Extend the light ray to show
how it travels in the fibre.
(ii)
The length and inner diameter of the fibre are 1 m and 0.5 mm respectively. How many
reflections will the light ray in (i) undergo if it travels through the fibre from end to end?
____________________________________________________________________
[Ans]
(a)
(i) The outer layer has a lower density than the inner layer so that the light in the fibre will be reflected
when it hits the boundary and be trapped inside the fibre. The light undergoes successive total internal
reflections in the fibre as shown above and the signal carried by the light is transmitted from one end to
the other.
(ii) Endoscopes / telecommunication
(iii) Less signal loss / less interference / lighter / corrosion free / less expensive / higher capacity (any
two of them)
(b)
(i)
(ii) ~1155
3C150205Q020Eng
(extension)
(a)
Draw a diagram to show how a light ray travels from a transparent material to the air through a
boundary. Mark the angle of incidence θi and the angle of refraction θr.
(b)
In this situation, the angles θi and θr are in fact related by:
nsin θi  sin θ r
where n is a constant called the refractive index of water. Its value is about 1.33.
(i)
Calculate the angle of refraction if the angle of incidence is 30o.
____________________________________________________________________
(ii)
Show that the angle of incidence at which the angle of refraction becomes 90 o is given by:
sin θi 
1
n
This angle is called the critical angle for total internal reflection.
____________________________________________________________________
(iii)
Calculate the critical angle for water.
____________________________________________________________________
186
Question Bank (Ch. 15)
(c)
Diamond has a relatively high refractive index of 2.42 and a small critical angle. Do you know how
this small critical angle contributes to the lustre of diamond?
__________________________________________________________________________
__________________________________________________________________________
[Ans]
(a)
(b)
(i) 41.7o
(iii) 48.8o
(c)
The small critical angle means that light coming from inside the diamond does not emerge out of the
diamond easily and will undergo a number of total internal reflections inside the diamond.
Miscellaneous Questions
3C150106Q001Eng
Match each of the objects on the left with the correct image in a plane mirror on the right. Write your answer
in the space provided.
Object
Image
(a)
(i)
(b)
(ii)
(c)
(iii)
(d)
(iv)
(v)
(vi)
(vii)
(viii)
(a) ______ (b) ______ (c) ______ (d) ______
[Ans]
(a) v
(b) vi
(c) viii
(d) iv
187
Question Bank (Ch. 15)
3C150106Q002Eng
Match the following radiations with their appropriate applications. Write your answer in the space provided.
Electromagnetic radiation
Application
(a)
X-rays
(i)
Measuring temperature
(b)
Microwaves
(ii)
Night vision
(c)
Ultraviolet radiation
(iii) Medical imaging
(d)
Gamma rays
(iv) Sterilisation
(e)
Radio waves
(v)
(f)
Infrared radiation
(vi) Luggage inspection
Signal transmission in mobile phones, TV, etc.
(a) ______
(b) ______
(c) ______
(d) ______
(e) ______
(f) ______
[Ans]
(a) iii, vi
(b) v (c) iv
(d) iv
(e) v
(f) i, ii
3C150106Q003Eng
Match the electromagnetic radiations on the left with the appropriate detectors on the right. Write your answer
in the space provided.
Electromagnetic radiation
Detector
(a)
Radio waves
(i)
Metal antennas
(b)
Infrared radiation
(ii)
Cone cells
(c)
Ultraviolet radiation
(iii) Photographic film
(d)
Visible light
(iv) Thermometer with a blackened bulb
(e)
X-rays
(v)
(a) ______
(b) ______
(d) ______
(e) ______
Fluorescent materials
(c) ______
[Ans]
(a) i
(b) iv
(c) v
(d) ii, iii
(e) iii
3C150106Q004Eng
Match the optical instruments on the left with their description on the right. Write your answer in the space
provided.
(extension)
Optical instrument
Description
(a)
Microscope
(i)
It can filter out the ultraviolet radiation in sunlight.
(b)
Endoscope
(ii)
It has great magnifying power for observing very
(c)
Sunglasses
(d)
Magnifying glass
(e)
Telescope
(f)
Periscope
(g)
Prism
small specimen.
(iii)
It consists of a convex lens and can produce a
magnified image for a close object.
(iv)
It enables the observer to observe a higher level
from a lower level.
(v)
It consists of optical fibres to observe the inside of
a human body.
(vi)
It is used for observing distant objects.
(vii)
It is a transparent, triangular block made of glass or
plastic.
(a) ______
(b) ______
(c) ______
(e) ______
(f) ______
(g) ______
(d) ______
[Ans]
(a) ii
(b) v
(c) i
(d) iii (e) vi
(f) iv
(g) vii
3C150106Q005Eng
(extension) Shown below are 6 pairs of physical quantities. For each pair, if we increase the quantity on the
left, determine whether the quantity on the right will increase too. If yes, put a ‘’ besides the pair. If not, put
a ‘’.
(a)
angle of incidence (regular reflection)
angle of reflection
(b)
frequency of an X-ray
(c)
distance between an object and a plane mirror distance between the mirror and the image
(d)
temperature of a body
infrared radiation emitted by the body
(e)
magnification of a lens
the image size for a given object
(f)
angle of incidence (total internal reflection)
energy carried by the X-ray
(a) ______
(b) ______
(c) ______
(d) ______
(e) ______
(f) ______
angle of reflection
[Ans]
(a) 
(b) 
(c) 
(d)  (e) 
(f) 
188
Question Bank (Ch. 15)
3C150206Q006Eng
Check the following ray diagrams. If there are mistakes, correct them.
(a)
(b)
(c)
[Ans]
(a)
(b)
The diagram is correct.
(c)
3C150206Q007Eng
Some white light plays the Ghost Leg as shown below. There are six entrances A to F. Find the colour of the
light that finally emerges from the Ghost Leg for each entrance.
_______________________________________________________________________________
_______________________________________________________________________________
[Ans]
A: black
B: red
C: white
D: green
E: black
F: green
189
Question Bank (Ch. 15)
3C150206Q008Eng
Shown below are three light rays. Place a prism over each of them so that their paths are possible.
(a)
(b)
(c)
[Ans]
(a)
Or:
(b)
(c)
3C150106Q009Eng
Complete the following colour charts.
(a)
red
(i)
(iii)
(ii)
green
blue
190
Question Bank (Ch. 15)
(b)
(i)
cyan
yellow
(ii)
red
(iii)
(iv)
(c)
(i)
cyan
(ii)
(iii)
(iv)
(v)
yellow
[Ans]
(a)
(i) yellow
(ii) white
(iii) magenta
(b)
(i) green
(ii) white
(iii) magenta
(iv) blue
(c)
(i) blue
(ii) magenta
(iii) white
(iv) green
(v) red
3C150106Q010Eng
Consider the following colours:
yellow
violet
red
blue
green
orange
indigo
Arrange them in increasing order according to
(a)
their frequencies.
__________________________________________________________________________
(b)
the amount of energy carried.
__________________________________________________________________________
(c)
the degree of bending when they travel from air to a prism.
__________________________________________________________________________
[Ans]
(a)
Red < orange < yellow < green < blue < indigo < violet
(b)
Red < orange < yellow < green < blue < indigo < violet
(c)
Red < orange < yellow < green < blue < indigo < violet
3C150106Q011Eng
Consider the following electromagnetic radiations:
microwaves
X-rays
ultraviolet radiation
visible light
gamma rays
radio waves
Arrange them in
(a)
increasing order of frequencies.
__________________________________________________________________________
(b)
increasing order of energy.
__________________________________________________________________________
(c)
decreasing order of penetrating power.
__________________________________________________________________________
191
Question Bank (Ch. 15)
[Ans]
(a)
Radio waves < microwaves < visible light < ultraviolet radiation < X-rays < gamma rays
(b)
Radio waves < microwaves < visible light < ultraviolet radiation < X-rays < gamma rays
(c)
Gamma rays > X-rays > ultraviolet radiation > visible light > microwaves > radio waves
3C150206Q012Eng
Determine whether the following methods can produce red light. Use ‘’ and ‘’ to indicate your answers.
(a)
Direct white light through a red filter.
[
]
(b)
Direct red light through a red filter.
[
]
(c)
Direct yellow light through a green filter.
[
]
(d)
Direct white light through a green filter then a red filter.
[
]
(e)
Direct red light through a green filter than a red filter.
[
]
(f)
Direct yellow light through a green filter than a blue filter.
[
]
[Ans]
(a) 
(b) 
(c) 
(d) 
(e) 
(f) 
3C150206Q013Eng
Each of the following parts contains some given information and a deduction. Determine whether the
deduction is correct. Use ‘’ and ‘’ to indicate your answer.
(a)
Information:
A student can see an object.
The student and the object are in a dark room.
All other things in the room are non-luminous.
Deduction:
The object is luminous. [
(b)
]
Information:
A student A sees the image of another student B in a plane mirror.
The image is of the same size as B.
The image is erect but laterally inverted.
Deduction:
The student B can see the image of A in the same mirror.
(c)
[
]
Information:
An object appears red when red light is shone on it.
The object is non-luminous.
The object appears blue when blue light is shone on it.
Deduction:
The object has a magenta colour when white light is shone on it. [
]
[Ans]
(a) 
(b) 
(c) 
3C150106Q014Eng
Classify the following objects into ‘luminous’ and ‘non-luminous’. Write your answer in the table below.
a book
the Earth
fire
the Sun
a switched-on computer monitor
the Moon
a silvery fork
a mirror
a switched-off computer monitor
a prism
water surface
Luminous object
a white shoe
a black shoe
diamond
Non-luminous object
[Ans]
Luminous object: fire, a switched-on computer monitor, the Sun
Non-luminous object: a book, a switched-off computer monitor, the Earth, the Moon, a mirror, a prism, a
white shoe, a black shoe, a silvery fork, water surface, diamond
192
Question Bank (Ch. 15)
3C150206Q015Eng
Four students A, B, C and D each has a card with a kind of electromagnetic radiation written on it. After
reading each other’s card, they make the following claims.
A:
My radiation is less penetrating than B’s, but more penetrating than those of C and D.
B:
My radiation has the highest frequency and C’s radiation has the lowest frequency.
C:
My radiation can be seen by the human eye while the others cannot.
D:
My radiation is often used to transmit TV signals while A’s radiation is used to check fake bank notes
and documents.
Only one of them is making a false claim. Who is this?
_______________________________________________________________________________
[Ans]
D
3C150106Q016Eng
Fill in the blanks with the appropriate colours. Each colour can only be used once.
red
green
yellow
indigo
blue
orange
violet
(a)
(i)____________ is a secondary colour that can be obtained by mixing red and (ii)____________.
(b)
____________ light lies between blue light and violet light in the electromagnetic spectrum.
(c)
____________ is the primary colour of light with the highest frequency.
(d)
The frequency of (i)____________ light is greater than that of (ii)____________ light but smaller than
that of yellow light.
[Ans]
(a)
(i) Yellow (ii) green
(b)
Indigo
(c)
Blue
(d)
(i) orange
(ii) red
3C150206Q017Eng
(extension) Here are several statements about light. Use ‘1’ and ‘0’ to indicate whether they are correct or not.
If you think a statement is correct in some cases and incorrect in other cases, give it a ‘*’.
(a)
When light is reflected at a plane mirror, the angle of incidence is equal to the angle of reflection.
(b)
When light refracts at the boundary between two media, the angle of incidence is larger than the angle
of refraction.
(c)
The magnification of the image formed by a convex lens is always greater than 1.
(d)
When light travels from medium to another, it will be reflected back at the boundary when the angle of
incidence is greater than a certain value.
(a) ______
(b) ______
(c) ______
(d) ______
[Ans]
(a) 1
(b) * (c) * (d) *
3C150106Q018Eng
Fill in the blanks with the appropriate electromagnetic radiation. Each radiation can only be used once.
radio waves
ultraviolet radiation
microwaves
(a)
gamma rays
visible light
X-rays
infrared radiation
In the electromagnetic spectrum, (i)____________ is the radiation just beyond violet light and
(ii)____________ is the radiation just beyond red light.
(b)
____________ are the radiation that has the lowest frequency in the electromagnetic spectrum.
(c)
____________ refers to the part of the electromagnetic spectrum that can be detected by the human
eye.
(d)
____________ are often used in signal transmission.
(e)
X-rays are the radiation that is between ultraviolet radiation and ____________ in the electromagnetic
spectrum.
[Ans]
(a)
(i) ultraviolet radiation
(b)
Radio waves
(c)
Visible light
(d)
Microwaves
(e)
gamma rays
(ii) infrared radiation
193
Question Bank (Ch. 15)
3C150106Q019Eng
(extension) Fill in the spaces below with ‘greater than’, ‘less than’ or ‘equal to’.
(a)
In a regular reflection, the angle of incidence of the light ray is ____________ the angle of reflection.
(b)
In a total internal reflection, the angle of incidence of the light ray is ____________ the angle of
reflection.
(c)
When a light ray travels from a denser medium to a less dense medium, the angle of incidence is
____________ the angle of refraction.
(d)
When a light ray travels from a less dense medium to a denser medium, the angle of incidence is
____________ the angle of refraction.
(e)
When an object is placed very close to a convex lens, the size of the image formed is ____________
the size of the object.
[Ans]
(a) equal to
(b) equal to
(c) less than
(d) greater than
(e) greater than
3C150106Q020Eng
(extension) Determine whether the following statements are correct or not. If not, write down the correct one.
(a)
All the objects that we can see emit light.
__________________________________________________________________________
(b)
Light of different colours has different frequencies.
__________________________________________________________________________
(c)
White light is a primary colour of light.
__________________________________________________________________________
(d)
A black object emits light of black colour.
__________________________________________________________________________
(e)
A red filter is a filter that absorbs red light only.
__________________________________________________________________________
(f)
Total internal reflection can occur only when light travels from a denser medium to a less dense
medium.
__________________________________________________________________________
[Ans]
(a)
All the objects that we can see either emit light or reflect light to our eyes.
(b)
The statement is correct.
(c)
White light is an appropriate mixture of all colours of light.
(d)
A black object does not emit light / absorbs all colours of light.
(e)
A red filter is a filter that allows only red light to pass through.
(f)
The statement is correct.
194