Hands-on Science Textbook Primary 4 (Chapter 02)

Chapter

2

Light

We have the Sun during daytime and electric lights
at night to brighten our world. Let’s know more about
this form of energy.

What do I know about light?
1.
2.
3.

What do I want to know about light?
1. Recognize that the Sun is our main source of light and it makes us see

clearly during the day.
2. Describe the properties of light.
3. Identify some of the uses of mirrors in daily life as a result of light

reflection.
4. Describe what happens when light strikes transparent, translucent

and opaque objects, and how shadows are formed.
5. Identify factors that cast shadows of different shapes and sizes.

2.1 Properties of Light

Light is a form of energy that enables us to see things around us. Light brightens
our world and makes things visible. During the day, the Sun is our main source of
light. Other than the Sun, we have other sources of light such as candles, electric
bulbs and torches. We are able to see different objects around us in the presence
of light.

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Slitgrehet taltanmigphst.with electric bulbs give us tThheerecaisnndoleeislecatrsicoiutyrcaet of light when
night.
16 Hands-on Science Primary 4

Many objects are not sources of light. However, we can see them during the
day because the Sun shines its light on the objects. The light from the Sun then
bounces off the objects. When the light enters our eyes, we can see the objects.
This is called reflection of light, that is, when light bounces off an object.
Can you see an object in the dark? why?

The light from
the Sun falls
on the kite.

The kite reflects
sunlight.

The girl can see
the kite because
the reflected light
enters her eyes.

Let’s Think

Based on the above situation,
what change do you notice
when the light from the Sun
bounces off the kite?

Chapter 2 Light 17

Light Travels in Straight Lines

Let’s Try! How does light travel?

Things needed: • Cardboards with a tiny • Matches
hole in the middle • Candle
• Wooden blocks • Pins
• Ruler

1. Pin each cardboard to a wooden block.

Cardboards with hole

20 cm 20 cm Lighted
candle

2. Place them 20 cm apart from one another so that the holes are in a straight
line and you can see through them.

3. Place a lighted candle at one end as shown.
4. Look at the candle through the holes. Can you see the candle flame?

5. Now, shift one of the cardboards to one side. Can you see the candle
flame?

6. Give one reason for your observation.

7. Place four pieces of cardboard in front of the lighted candle at different
positions A, B, C and D as shown.

B

A
C

D

18 Hands-on Science Primary 4

8. Can you see the candle flame through the cardboards at positions A, B, C
and D?

9. Give one reason for your observation above.
10. What is your conclusion from this activity?

The Sun is very far from our Earth but its light travels very fast.
Sunlight takes about 8 minutes to reach Earth.

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Light

Chapter 2 Light 19

Reflection of Light

When light strikes an Sunlight
object with a smooth passes
surface, the surface through the
reflects the light in the window.
same direction. Then,
we can see the object Light is reflected.
when the reflected light
enters our eyes.

Reflected rays on a smooth surface

This table is smooth so it reflects the light
evenly in the same direction. We can see the
image of the father and son on the table. The
table appears shiny.

If the surface is rough, the light rays are
reflected in different directions.

Reflected rays on a rough surface

For example, if we look at the tiles, light has
reflected off them and traveled in nearly all
directions. The tiles appear dull.

20 Hands-on Science Primary 4

Let’s Try! How many times can light be reflected?

Things needed: • Torch
• Mirrors
• A piece of cloth with a small hole in the middle

1. Carry out this activity in a dark room. Mirror
2. Wrap the torch with the cloth. Cloth with a hole
3. Shine the torch through the hole onto
Torch
the mirror at an angle as shown.
4. What have you observed?

5. Add a mirror in the path of the reflected light. How is the light reflected for
the second time? Draw what you have observed.


6. What happens if another mirror is placed in the path of the reflected light?

7. What is your conclusion from this activity?

Chapter 2 Light 21

Mirrors can reflect all the light rays
that fall on them perfectly because
they have a smooth surface. For
example, a mouth mirror is used by
the dentist to view a mirror image
of teeth in locations where they are
difficult to see.

We use rear view mirrors to see
things behind us or to view things

at our sides.

Other than those examples above,
how do we see things that cannot be
seen directly from where we are? For
example, things that are higher than
us or around the corner.

Let’s Think

When we look at the water surface,
we can see the castle, sky and
trees reflected on it. Why?

22 Hands-on Science Primary 4

Let’s Try! How do we make a periscope?

• Two empty • Masking tape

milk cartons • Two small rectangular-

Things needed: • Cutter shaped mirrors

• Pencil (about five by seven

• Ruler centimeters)

1 2
10 3
4

5

98 76

Chapter 2 Light 23

1. Cut off the top of the two empty milk cartons.

Make sure they are clean and dry before you

cut. A cutter is very sharp.
2. Cut a rectangular hole at the bottom of one Let your teacher do all
the cutting in this activity.
carton. This is your viewing window. If you are preparing it at
3. Put the carton on its side so that the window is home, have your parents
to join you in this activity.
facing the right. Draw a line from the bottom

right-hand corner to where it meets the left-

hand edge. It is important to make sure that

the line drawn is at the angle of 45 degrees.

4. Make a cut on that line with a length of one

side of your mirror. If your mirror is thick,

widen the cut to ensure your mirror can fit

in.

5. Insert the mirror through the slot. The

reflecting side must face the window. Tape

the mirror loosely in place.

6. Hold the carton up to your eye level and look

through the viewing window. You should see

your ceiling in the mirror. If what you see

looks tilted, adjust the mirror and tape it again.

7. Repeat steps 2 to 6 with the second milk carton.

8. Place one carton up on the table with the window facing you. Place the

second carton on top with the window facing away from you.

9. Pinch the open end of the top carton a little so that it can slide into the

bottom carton. Tape the two cartons together securely.

10. Now your periscope is ready. Hold it upright.

(a) If you look through the bottom viewing window, you can see things
that are higher than you.

(b) If you look through the top viewing window, you can see things that
are under tables.

(c) If you hold it sideways, you can see around corners.
11. What will happen to the image formed if we make the tube longer?

12. What is your conclusion from this activity?

24 Hands-on Science Primary 4

Periscope comes from two Greek words, peri and scopus. Peri
means ‘around’ and scopus means ‘to look’. A periscope lets us
look around the corner, at things that are out of sight or behind
a high obstacle.

A periscope is an instrument with a long tube
containing a set of mirrors. The mirrors in it reflect
light so that we can see at things that cannot be
seen directly from where we are.

Periscope

Submarine Submarines have periscopes. The
periscope enables the sailors inside
the submarine to see things on the
water surface even if they are below
the water level.

Let’s Find Out!

Mirrors are used widely in our daily life. What are the other uses of mirrors?
Find out examples and share your findings with your friends in class.

Chapter 2 Light 25

2.2 Shadows

Light travels in straight lines as long as it does not hit anything. When light hits an
object, it may be reflected or pass through the object. This depends on the nature
of the object.

Light When light hits a transparent object, the
light passes through it. Therefore, we
can see through transparent objects. Air,
water, clear glass and clear plastics are
transparent objects.

Light passing through a transparent object

Light

Translucent objects allow only some light
to pass through them. So, objects behind
them appear blurred. Tracing paper and
frosted glass are translucent objects.

Some light passing through a
translucent object

Light

Shadow

A shadow is No light passing through an
formed when light opaque object

is blocked by an Opaque objects do not allow light
opaque object. to pass through them at all. Trees
and rocks are examples of opaque
objects.

26 Hands-on Science Primary 4

Let’s Try! How do we make a shadow bigger or smaller?

Things needed: • Torch • Cylindrical
• Meter ruler wooden block

A Position of the object
1. Place the meter ruler on a table. Place its end with the zero-mark against a

wall.
2. Place the cylindrical wooden block upright 10 cm away from the wall.
3. Then, place the torch at the position of 20 cm.

Wall

Wooden block

Torch Meter ruler

10 cm 20 cm

4. Turn on the torch. Make sure the room is dark enough to observe the
shadow.

5. Draw the shape of the shadow formed in the space below.

Position of the Upright Horizontal
wooden block

Shape of the
shadow formed


6. Repeat steps 1 to 5 by placing the wooden block in a horizontal position

10 cm away from the wall.
7. Let the position of the wooden block remain unchanged. Now, hold the

torch at any angle above the wooden block. What happens to the size and
the shape of the shadow formed?

8. What is your conclusion from this activity (Part A)?

Chapter 2 Light 27

B Distance between the object and the light source
1. Place the meter ruler on a table. Place its end with the zero-mark against a wall.
2. Place the cylindrical wooden block upright 10 cm away from the wall.
3. Then, place the torch at the position of 20 cm.

Wall

Wooden block

Torch Meter ruler

10 cm 20 cm

4. Turn on the torch. Make sure the room is dark enough to observe the shadow.
5. Measure the height of the shadow formed and record it in the table below.

Distance between the wooden Size of the shadow formed
block and the torch (cm) (cm)

10
20

30
6. Repeat steps 2 to 5 by placing the torch at the positions of 30 cm and 40 cm.

Questions
1. What condition remains unchanged in this activity?

2. What condition changes to make the size of the shadow formed either
smaller or bigger?

3. How do you make the shadow formed become bigger in this activity?

4. What happens to the shape of the shadow formed?

5. What is your conclusion from this activity (Part B)?

28 Hands-on Science Primary 4

C Distance between the object and the screen
1. Place the meter ruler on a table. Place its end with the zero-mark against a wall.
2. Place the cylindrical wooden block upright 10 cm away from the wall.
3. Then, place the torch at the position of 50 cm.

Wall

Wooden block

Torch Meter ruler

10 cm 50 cm

4. Turn on the torch. Make sure the room is dark enough to observe the shadow.
5. Measure the height of the shadow formed and record it in the table below.

Distance between the wooden Size of the shadow formed
block and the wall (cm) (cm)

10

20

30

6. Repeat steps 2 to 5 by placing the wooden block 20 cm and 30 cm away
from the wall.

Questions
1. What condition remains unchanged in this activity?

2. What condition changes to make the size of the shadow formed either
smaller or bigger?

3. How do you make the shadow formed become bigger in this activity?

4. What is your conclusion from this activity (Part C)?

An object can cast shadows of different shapes and sizes depending on
• the position of the object and the direction of the light shining on it
• the distance of the object from the light source
• the distance of the object from the screen

Chapter 2 Light 29

Fill in the blanks.

periscope   bigger   straight   all   rough   shadow
transparent   smaller   smooth   translucent   reflection   opaque

1. Light travels in a line and in directions.

2. When light bounces off an object, the of light happens.

3. When light strikes a surface, it is reflected in the same direction.

4. When light strikes a surface, it is reflected in different directions.

5. We use a to see things that cannot be seen directly from
where we are.

6. Objects that allow light to pass through them are objects.

7. Objects that allow some light to pass through them are objects.

8. Objects that do not allow light to pass through them are objects.

9. When light is blocked by an opaque object, a is formed.

10. When the light source is farther from the object, the shadow formed is

. When the light source is closer to the object, the shadow

formed is .

Let’s Scan

30 Hands-on Science Primary 4

Map It Out

Properties of Light Light

• Light travels in straight Shadows
lines and in all
directions. • A shadow is formed when light is
blocked by an opaque object.
• Reflection of light.
• The greater the distance
between the object and the light
source, the smaller the shadow
formed.

• The greater the distance
between the object and the
screen, the bigger the shadow
formed.

Explain It Online

QuickQuiz

Bounce off

To move away after hitting a surface

Submarine

A ship that can travel under water

Visible

Able to be seen

Chapter 2 Light 31