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Unit 6P.2: Light

What is Light?

Shadows

Reflection

The colors of the rainbow

Science skills:

Observing

Classifying

Predicting

By the end of this unit you should:

Know that light moves in straight lines.

Know how shadows are formed.

Know that light has a very high velocity.

Know how we see things.

Know that objects can absorb or reflect light.

Know what the white color is.

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What is Light?

Can you imagine what the world would be like without light?

You would not be able to see the world around you. Plants

could not grow, and you would not have any food to eat.

Light is all around you, but maybe you don't think about it

very often! Light has some very special things about it.

Some objects make light, such as the sun, a candle, a big

fire or a light bulb. We call these sources of light. Sources

of light actually glow.

If you put them into a completely dark room, they would still

glow and you would still be able to see them.

These are examples of sources of light.

Light is a form of energy.

Sources of light are objects that give out light

6.16.1 , 6.16.2

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There are other things that look as though they are sources of

light because they appear to shine, such as the moon, mirrors

and aluminum foil. These are not sources of light, but they

reflect the light that shines onto them (illuminated objects).

If you put them into a completely dark room, they would not glow

and you would not be able to see them. Can you think of another

object?

Moon Aluminium Foil Mirror

The pictures a above show illuminated objects

Illuminated objects are objects that reflect the light

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Sources of Light - Look at the table below, Identify which of the following are light

sources, circle the ‘Sources of Light’ ONLY .

Diamond The Sun CD

The Moon Television Swords

Candle Rainbow Mirror

Lightning Firefly Light Bulb

Cat’s Eye Fireworks Eyes

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Facts about light: Speed of light:

Activity: Thunder and lightning.

During a thunder storm, do you see the lightning first or do

you hear the thunder first?_____________

You see the lightning before you hear the thunder.

They happen at the same time but the thunder takes longer to

reach your ears.

Some kids were discussing what they felt after they saw a

storm! Who do you think is right?

Light travels very fast – faster than sound

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Light travels very quickly. Light is much faster than sound.

When you put your torch on, the light leaves the bulb

and hits the wall, it takes a very very very small amount of

time.

The time taken for the light to leave

from here…

..and then hit the wall here feels like

it take no time! But it does.

If you had a powerful flashlight

And shone it to the moon it would take about a second to reach there!

The time taken for the sun’s light to reach us taken about 8 minutes! It travels 150 million km!!!

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How does light travel?

When a can with holes, is placed over a candle, light will

shine through the holes. If we sprinkle chalk dust into the

air around the can, we will be able to see how the light is

traveling

You can see the same effect when using the data show in a

dark room. If you look up at the projection beam, dust in

the air will show the beam of light traveling straight to the

screen.

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Activity: How Light Travels

You will need: torch, boxes, rubber tube (ie shoes), and

cardboard.

Steps:

Construct the boxes shown in pictures.

Experiment 1: Down the tube

1 Look down one of the rubber tubes.

2 Change the shape of the tube until you

can see light at the other end.

What shape must the tube be for you to see the light?

________________________________________

Experiment 2: Making a path

1 Move the two sliding panels until the

light comes out of the hole nearest you

and enters your eye.

2 Take the lid off the box.

What do you notice about the four holes?

________________________________________

Experiment 3: Shadows - you will need some paper and

scissors

1 Turn on the light source.

2 Make a circular shadow on the screen.

3 Make the circular shadow bigger.

4 Make a square shadow on the screen.

5 Make the square shadow smaller.

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Conclude - Discuss the following questions in your group. Use

your observations to back up your conclusions.

What did you use to make:

a. the circular shadow?

_____________________________________________

b the square shadow?

_____________________________________________

What did you do to make the shadow:

a larger?

b smaller?

_____________________________________________

Key words

Light

Sources of light

Reflecting light

Speed

Thunder

Straight line

Key Ideas

Objects that give out light are

called sources of light.

Some objects reflect light.

Light is very fast

Light travels in straight lines.

Light travels in straight lines

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Q(1) Classify the following according to whether they are

illuminated objects or sources of light.

The Sun, the Moon, a star, the planet Jupiter, a laser, a

mirror, a light bulb, a fire.

sources of light illuminated objects

Shadows in more detail…

We know light travels in straight lines.

When light hits a transparent object, like

glass, it can pass through.

Project

Using a torch, water bottle with a sprinkler.

Design an experiment to see how light travels.

6.16.1

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Light

When it hits an opaque object, like wood, it cannot pass

through and a shadow is formed.

A shadow shows us where the light has not passed through an

object, so the shadow is the same

general shape as the object.

You can make a shadow using a powerful torch and cutting

out a shape on a piece of thick card! Make an animal you like!

Even use your hands!

The cat puppet blocks the light and a shadow is formed on

the screen. Using a ruler and a pencil, we can draw a

diagram to show where the shadow is made.

Shadows are formed when opaque objects block the light

source of light.

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Activity: Making shadows.

You will need:

Torch, pencil/straw, clay.

Steps:

1- Make an animal shape using clay.

2- Hold the torch above the object and shine it straight

down?

What do you observe? --------------------------.

3- What happens when you shine the torch to the side of

the object?

-------------------------------------------------

Move your flashlight in a circle above the object. What

happens to its shadow (length and direction )?

-------------------------------------------------

-------------------------------------------------

Shadows made by sun light:

On a sunny day you will see many shadows.

This shade is the shadow formed by the tree

blocking the sun light.

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Have you ever wondered how people discovered how to tell

the time?

They used the position of the Sun in the sky to mark the

shadows on sundials. You can tell the time by looking at the

shadow cast by the Sun as it shines on the pointer of a

sundial. The proper name for the pointer is a gnomon.

Make your own Sundial/Gnomon:

1. In pairs stick a pencil or straw

on a plain piece of A4 paper.

2. You can use sellotape and clay to

fix it in the position.

3. Go outside where the sun is

shining.

4. Place the paper in the sunlight

5. Mark the shadow on your paper

with a line and write the time

above it.

6. After 5 min look at your paper

again…the shadow should have

moved!

7. Repeat step 5.

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Key words

Shadow

Sundial

Key Idea

Shadows are formed when the

light hits something opaque and it

cannot travel through.

Key Questions

Q(1) How is a shadow formed?

---------------------------------------------

Q(2) Underline the right word:

Light can travel through (transparent/ opaque) materials.

Q(3)This picture shows the sun casting light on a round

object. Label the diagram.

Shadow

Light source

Object

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Shadows

Use the words in the box to fill the gaps below!

shorter opposite longer larger

smaller

1. The nearer the object is to the light source the

_______________ the shadow.

2. The higher the light source the _______________ the

shadow.

3. The closer the object is to the light source the

_________________ the shadow.

4. The lower the light source the _______________ the

shadow.

5. The shadow is always on the _________________ side

of the object to the light source.

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Light

Reflection

We see only when there is a light source. We can see the

sun because it gives out light which shines into our eyes.

The candle flame is a light source when light travels from

the candle flame into our eyes, we see the flame.

There are other things that we can see but they are not

sources of light. They reflect the light that shines on them,

we say they are illuminated.

The light hits the rabbit and bounces off. Then the light

enters our eyes and we see the rabbit.

6.16.3, 6.16.4

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The light from the lamp hits an object and bounces off, then

enters our eyes and allows us to see the object.

Not all materials reflect (bounce) light in the same way:

Type Definition

Shiny materials

materials reflect light that shines on

them without scattering the rays. They

usually have a smooth surface

Dull materials

materials scatter the light rays and

reflect them in different directions.

They usually have rough surface .

Dark objects

materials do not reflect the light rays

well because they absorb the light.

Shiny objects reflect the light better than dull objects.

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Activity: Go round the school or science area with a torch

and write down as many objects you could find that had

reflective surfaces:

Object and location…. I can

see

my

face

…

It

reflects

torch

light

Is this object made

from this material

because it is reflective?

Why?

Mirror – windows from

outside

Yes.

Mirrors are very reflective so that

you can see your reflection clearly

.

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Key Question

Q1: Explain why we can see objects during the day but we

cannot see the same objects when it is dark.

-------------------------------------------------

-------------------------------------------------

Q2: Tariq dazzles his friend at the other side of the

classroom by reflecting sunlight from his watch. Tarik’s arm

is lit up by the Sun. Explain why everyone can see his arm

but only his friend is dazzled by his watch.

------------------------------------------------

------------------------------------------------

------------------------------------------

Key Words

Illuminated

Reflect

(bounce)

Shiny

Scatter

Dull

Dark

Key Ideas

We see objects when light

from them enters our eyes.

Materials can be shiny, dull

or dark.

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The colors of the rainbow.

White light is made up of many

colors mixed together. A prism can

separate the colors.

Rain drops act like prisms to form rainbows. It shows us that

white color is not just one color. It is lots of different

colors mixed together.

The colors of rainbow are:

Red, Orange, Yellow, Green, Blue, Indigo and Violet.

The light BENDS twice, once when it passes from air into

glass and again when it passes from glass into air.

6.16.5

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Activity 1: Making rainbow

You will need:

Small mirror, Clear glass, Water, and Flash light.

Steps:

1. Gently place the mirror into the glass. Slant it up

against the side.

2. Fill the glass with water. (picture A)

3. Set the glass on a table. Turn out the lights.

Make the room as dark as possible.

4. Shine the flash light into the glass of water. Aim for

the mirror. Adjust your aim until the light hits the mirror.

5. Observe what happens to the light in the glass. Look at

the light where it hits the ceiling or the wall. Record what

you observe. (picture B)

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Light

Light is made up of coloured light. Mixtures of coloured

light is combined to form white light.

Making white light from coloured light

You will need:

White cardboard, Scissors, (120 cm works well), Pencil,

Steps:

1- Cut out the circle on the right using

some scissors.

2- Colour in the segments using colouring

pencils.

3- Stick blu-tack on the back of the disc in the middle.

4- Stick the end of a pen or pencil into the blu-tack.

5- Hold the pen in between your two hands and rub them

together to make the disc spin.

6- What colour do you see when the disc is spinning?------

Light and color of objects:

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The colors of object that you can see are the

colors of light that the objects reflect.

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Key Words

Illuminated

Reflect

(bounce)

Shiny

Scatter

Dull

Dark

Prism

Rainbow

Key Ideas

We see objects when light

from them enters our eyes.

Materials can be shiny, dull

or dark.

White light is made up of

many colors mixed together.

The colors of object that you

can see are the colors of

light that the objects

reflect.

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Key Questions

1. Look at the picture below. Draw direction arrows

on the beam of light to show how the girl can see the

balloon.

2. Complete the sentences below to explain what is

happening in the picture.

a. The light travels from the _________ to the

balloon.

b. The light bounces off the balloon and enters the

girl's __________

3. What are the colors that make white light?

________________________________________

4. Which color will reflect from the balloon?

________________________________________

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Light wordsearch

Below are some words associated with ‘Light’. Can you find

them all?

S R A I N B O W B D

E H L S A O P R L A

F V A M S L R E I R

G N R D W T T F G K

T A G C O Y Y L H T

O D I M C W U E T R

R C I E N S S C Y E

C F B R I G H T H L

H H O W M P G H D K

S I P Q J O S U N I

T U T F H I Q B T J

L U M I N O U S H U

Bright

Sun

Reflect

Rainbow

Dark

Torch

Shadow

Light

Dim

Luminous