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Primary Science · Year 3Chapter 8 · Light and shadows
Year 3 · Chapter 8

Light and shadows

By the end of this chapter you will be able to

  • Say that we need light to see things, that dark is the absence of light, and that we see an object when light from it enters our eyes
  • Name light sources, such as the Sun, a torch and a lamp, and tell them apart from things that only reflect light
  • Explain that light bounces off shiny surfaces such as mirrors, and that dull surfaces scatter light
  • Say why we must never look directly at the Sun, and name ways to protect our eyes from its light
  • Explain that a shadow forms when an opaque object blocks the light from a light source, and name what is needed for a shadow
  • Read a fair test on shadow size, find the pattern, and explain how the shape of a shadow depends on the object and the light

You should already know

  • The senses, and the body parts used to see and hear (Year 1 and Year 2 Science)
  • Fair tests, and changing only one thing at a time (Year 3 Science, Chapter 1)

Where this leads

  • Forces, and how things move on different surfaces (Year 3 Science, Chapter 9)
  • Light and how we see, in more detail (Year 6 Science)

National Curriculum for England, Key Stage 2 science, Year 3. Content: L1 recognise that they need light in order to see things and that dark is the absence of light, L2 notice that light is reflected from surfaces, L3 recognise that light from the Sun can be dangerous and that there are ways to protect their eyes, L4 recognise that shadows are formed when the light from a light source is blocked by an opaque object, L5 find patterns in the way that the size of shadows change.

Exercise P  Do you remember?

1
FWhich body part do you use to hear? Write the word.
2
FWhat do muscles pull on to make a body part move? Write one word.
3
FWhen we do a fair test, how many things do we change? Write the number word.
4
FHow many legs does an insect have? Write the number.
5
FWhat is the top layer of the ground, where plants grow, called? Write the word.
8.1

Light and seeing

Year 3
L1: recognise that they need light in order to see things and that dark is the absence of light
Video lesson: Light and seeingComing soon
Story. Amira is in her bedroom at bedtime. The lights are off, and she cannot find her book. She switches on the lamp, and she can see it at once. “Why can I only see my book when the light is on?’ she asks.

We need light in order to see things. Light from a light source, such as the Sun or a lamp, lands on objects and bounces off them. When that light enters your eyes, you see the object.

Dark is the absence of light. It means there is no light at all. In a dark room, no light enters your eyes, so you cannot see anything.

Look at the two pictures. In the first picture the lights are off, so no light enters the eyes. In the second picture the lights are on, so light from the lamp bounces off the cup and enters the eye.

Lights off:no light enters the eyeslampLights on:light enters the eyes
Left: lights off, so no light enters the eyes. Right: lights on, so light enters the eyes.

The table shows what happens in three different situations.

SituationDoes light enter your eyes?Can you see the cup?
Lights on, and a cup in front of youyesyes
Lights off, and no torch is onnono
Lights off, and a torch shines on the cupyesyes

Key ideas

  • We need light in order to see things.
  • We see an object when light from it enters our eyes.
  • Dark is the absence of light: there is no light.
  • In the dark, no light enters the eyes, so we cannot see.
Worked example 8.1.1
Look at the table in this section. When the lights are off and a torch shines on the cup, does light enter your eyes? Write yes or no.

Method. Find the right row of the table.

  1. Find the row. The third row says lights off, and a torch shines on the cup.
    third row
  2. Read the column. The column Does light enter your eyes? says yes for that row.
    yes
  3. Write the answer.
    yes

Check. The torch lets light reach the cup, and the light enters the eyes. ✓

Watch out. Read the column headed Does light enter your eyes? for the row you want.

Worked example 8.1.2
Look at the table in this section. Can you see the cup when the lights are off and no torch is on? Write yes or no.

Method. Find the second row of the table.

  1. Find the row. The second row says lights off, and no torch is on.
    second row
  2. Read the last column. The column Can you see the cup? says no for that row.
    no
  3. Write the answer.
    no

Check. No light enters the eyes, so the cup cannot be seen. ✓

Worked example 8.1.3
Explain in one short sentence why you can see your book when the lamp is on.

Method. Think about the path of the light.

  1. Follow the light. Light from the lamp lands on the book.
    lamp to book
  2. Finish the path. The light bounces off the book and enters your eyes.
    enters your eyes
  3. Write the answer.
    Light from the lamp bounces off the book and enters your eyes.

Check. Light must enter the eyes before we can see the book. ✓

Watch out

Watch out: your eyes do not make light. We can see because light from outside the eyes enters them.

Try it at home or school (with a grown-up). Sit in a room with the curtains closed. Switch off the lights and wait one minute. Say what you can see and what you cannot. Then switch on a torch, and point it at a book, away from your face. Switch the torch off before you put it down. Never shine a torch into anyone’s eyes.

Exam tip

Grown-up tip. Ask: “Why can you see the book now? What is the light doing?” Let your child explain the path of the light, from the torch to the book and into the eyes, in their own words.

Exercise 8A  Light and seeing

1
FLook at the picture of the eyes. In which picture can you see the cup: lights on or lights off? Write the words.
Lights off:no light enters the eyeslampLights on:light enters the eyes
2
FIs it dark when no light reaches your eyes? Write yes or no.
3
FFill in the gap: dark means there is ___ light. Write the word.
4
FWhich part of the body do we use to see? Write the word.
5
FLook at the table in this section. In a dark room with no torch on, can you see the cup? Write yes or no.
6
FWe see an object when light from it enters our ___. Write the word.
7
FTrue or false: your eyes make the light that lets you see. Write true or false.
8
FLook at the table in this section. When the lights are on, can you see the cup? Write yes or no.
9
PSSam says he can see his shoes in the dark because his eyes make their own light. Is Sam right? Write no or yes.
10
PSWorking scientifically. Predict what you will see if you switch on a torch in a dark cupboard and shine it on a teddy. Write one prediction.
11
RExplain why a room with no light looks completely dark to you. Write one sentence.
8.2

Light sources

Year 3
L1: recognise that they need light in order to see things; light sources such as the Sun, a torch and a lamp
Video lesson: Light sourcesComing soon
Story. Mo is in the garden at night. He asks, “Which things make their own light?” Priya says, “The torch does. The chair doesn’t.” Mr Patel says, “Let’s sort them into two groups.”

A light source is something that makes its own light. The Sun, a torch and a lamp are light sources.

Most things do not make their own light. We see a book, a chair or a cup because light from a light source reaches them, and bounces off them into our eyes. They are not light sources.

SunTorchLampBookChairCup
Top row: a sun, a torch and a lamp, which are light sources. Bottom row: a book, a chair and a cup, which are not light sources.
ThingMakes its own light?
Sunyes
Torchyes
Lampyes
Bookno
Chairno
Cupno

Key ideas

  • A light source is something that makes its own light.
  • The Sun, a torch and a lamp are light sources.
  • A book, a chair and a cup are not light sources.
  • We see things that are not light sources when light from a light source bounces off them.
Worked example 8.2.1
Look at the table in this section. How many light sources are in the table? Write the number.

Method. Count the rows that say yes in the column Makes its own light?

  1. Read the column. The Sun, the torch and the lamp say yes.
    Sun, torch, lamp
  2. Count them. There are three light sources in the table.
    3
  3. Write the answer.
    3

Check. The three things that say no are the book, the chair and the cup. ✓

Worked example 8.2.2
Is a chair a light source? Write yes or no.

Method. Think about whether a chair makes its own light.

  1. Look at the table. The chair says no in the column Makes its own light?
    no
  2. Decide. A chair does not make its own light, so it is not a light source.
    no
  3. Write the answer.
    no

Check. We see a chair because light bounces off it. ✓

Worked example 8.2.3
Name a light source that shines in the sky in the daytime. Write the name.

Method. Think about what gives us light in the day.

  1. Think about the sky. In the daytime, the bright light in the sky comes from the Sun.
    the Sun
  2. Write the name. That light source is the Sun.
    Sun
  3. Write the answer.
    Sun

Check. The Sun makes its own light. ✓

Watch out

Watch out: the Moon is not a light source. It shines because it reflects light from the Sun.

Try it at home or school (with a grown-up). With a grown-up, walk round your home. Find three things that make their own light, and three that do not. Only switch things on and off with a grown-up. Do not touch a lamp bulb that has just been on, because it can be hot. Never look straight at a very bright light.

Exam tip

Grown-up tip. Ask: “Does this thing make its own light? How can you tell?” Let your child use the words light source, and check the answer by switching the thing on.

Exercise 8B  Light sources

1
FLook at the table in this section. Which thing that makes its own light is in the sky in the daytime? Write the name.
2
FIs a cup a light source? Write yes or no.
3
FWrite the name of a light source that you can switch on in a room. Write one name.
4
FLook at the table in this section. How many things in the table are not light sources? Write the number.
5
FWhich is a light source: a book or a torch? Write the word.
6
PSSort these into light sources: sun, book, torch, chair, lamp, cup. Write the light sources.
7
FFill in the gap: a torch is a light ___. Write the word.
8
FTrue or false: the Moon makes its own light. Write true or false.
9
PSTrue or false: a book is a light source, because we can see it. Write true or false.
10
PSWorking scientifically. Plan how to find out whether an object is a light source. Write one step.
11
RPredict whether you will see a book in a dark room if a torch shines on it. Write yes or no, and give one reason.
8.3

Light bounces off surfaces

Year 3
L2: notice that light is reflected from surfaces, including mirrors
Video lesson: Light bounces off surfacesComing soon
Story. Fatima shines a torch at a small mirror, and a bright spot appears on the wall. “Where did the light go?’ she asks. Mr Patel says, “It bounced off the mirror. That is called reflection.”

Light can bounce off a surface. This is called reflection. When light is reflected, we say it is reflected from the surface.

A mirror is very smooth and shiny. It reflects a lot of light in one clear direction, so the spot on the wall is bright and clear. A dull, rough surface scatters light in many directions, so the spot is soft or faint. A dark surface reflects very little light.

torchlight bounces offlight comes inthe mirror
A torch shines at a mirror. The light bounces off the mirror in a new direction.
Shiny surface:light bounces off one wayDull surface:light scatters in many directions
Left: a shiny surface reflects light in one clear direction. Right: a dull surface scatters light in many directions.

Priya tested five surfaces in the same dark room, with the same torch. She shone the torch at each surface, and looked at the spot on the wall.

SurfaceShiny or dull?What the torch shows on the wall
Mirrorshinya clear, bright spot
Kitchen foil, flat and smoothshinya bright spot
White paperdulla bright, soft spot
Wooden tabledulla faint spot
Black carddullno spot that you can see

Key ideas

  • Light can bounce off a surface. This is called reflection.
  • A mirror is a smooth, shiny surface that reflects light clearly.
  • Dull surfaces scatter light in many directions, so the spot is soft or faint.
  • A dark surface reflects very little light.
Worked example 8.3.1
Look at the table in this section. How many surfaces made a bright spot? Write the number.

Method. Find the surfaces with a bright spot in the last column.

  1. Read the last column. The mirror, the kitchen foil and the white paper all made a bright spot.
    mirror, foil, paper
  2. Count them. Three surfaces made a bright spot.
    3
  3. Write the answer.
    3

Check. The wooden table made a faint spot, and the black card made no spot. ✓

Worked example 8.3.2
Look at the table in this section. Which surface made no spot that you can see? Write the surface.

Method. Find the row that says no spot in the last column.

  1. Read the last column. The black card says no spot that you can see.
    no spot
  2. Write the surface. So the surface is the black card.
    Black card
  3. Write the answer.
    Black card

Check. A dark surface reflects very little light. ✓

Worked example 8.3.3
Look at the table in this section. Which surface made the clearest spot? Write the surface.

Method. Look for the clear spot in the last column.

  1. Read the last column. The mirror made a clear, bright spot, with a sharp edge.
    clear, bright
  2. Write the surface. So the clearest spot came from the mirror.
    Mirror
  3. Write the answer.
    Mirror

Check. A mirror is smooth and shiny, so its reflection is clear. ✓

Watch out

Watch out: a reflection is not a light source. The mirror does not make light. It only bounces light from the torch.

Try it at home or school (with a grown-up). In a room with the curtains closed, with a grown-up, shine a torch at a small mirror. Watch the bright spot move on the wall as you tilt the mirror. Never point the torch or the mirror at anyone’s eyes. Switch the torch off when you finish.

Exam tip

Grown-up tip. Ask: “Where did the light go after it hit the mirror? Why is the spot on the wall bright?” Let your child use the words reflect, reflection and shiny.

Exercise 8C  Light bounces off surfaces

1
FLook at the table in this section. Is the mirror shiny or dull? Write the word.
2
FWhat is the name for light bouncing off a surface? Write the word.
3
FLook at the table in this section. Did the wooden table make a bright spot or a faint spot? Write the word.
4
FLook at the table in this section. How many surfaces are shiny? Write the number.
5
FLook at the table in this section. Which dull surface made a bright, soft spot? Write the surface.
6
FFill in the gap: a mirror is very smooth and ___. Write the word.
7
FLook at the picture of the mirror. Does the light bounce off the mirror? Write yes or no.
torchlight bounces offlight comes inthe mirror
8
FTrue or false: a mirror makes its own light. Write true or false.
9
PSAli says a black card makes a bright spot on the wall, because it is dark. Is Ali right? Write no or yes.
10
PSWorking scientifically. Which surface would you use to bounce light from a torch into a dark corner? Write the surface.
11
RExplain why the spot from the white paper is soft, but the spot from the mirror is clear. Write one sentence.
8.4

Never look directly at the Sun

Year 3
L3: recognise that light from the Sun can be dangerous and that there are ways to protect their eyes
Video lesson: Never look directly at the SunComing soon
Story. Noah is at the park on a sunny day. He looks up at the bright sky, straight at the Sun, and his eyes feel sore. Mr Patel says, “Never look straight at the Sun. Look away, and let’s find out how to protect your eyes.”

The Sun is a light source. Its light is very bright, and it can damage your eyes. You must never look directly at the Sun, not even for a second.

Do not look at the Sun through binoculars, a telescope or a camera either. These make the light stronger, so they are even more dangerous. Sunglasses do not make it safe to look at the Sun.

There are ways to protect your eyes from the Sun:

Never use a mirror to flash sunlight into someone else’s eyes.

Never look at the SunLook away. Wear a hat.
Left: never look at the Sun. Right: look away, and wear a hat with a brim.

The table shows some actions. Some are safe for your eyes, and some are not.

ActionSafe for your eyes?
Look straight at the Sunno
Look at the Sun through binocularsno
Stare at the Sun through sunglassesno
Use a mirror to flash sunlight into someone's eyesno
Wear a hat with a brim on a sunny dayyes
Stand in the shadeyes
Wear sunglasses that block UV light on a sunny dayyes
Look away from the Sun, down at the ground or at your shadowyes

Key ideas

  • Never look directly at the Sun, even for a second.
  • Sunglasses do not make it safe to look at the Sun.
  • Binoculars and telescopes make the Sun even more dangerous to look at.
  • Look away, wear a hat with a brim, stand in the shade or wear sunglasses that block UV light.
  • Never use a mirror to flash sunlight into someone else’s eyes.
Worked example 8.4.1
Look at the table in this section. Is it safe to look at the Sun through binoculars? Write yes or no.

Method. Find the row about binoculars.

  1. Read the row. The row says look at the Sun through binoculars, and the answer in the last column is no.
    no
  2. Write the answer. So it is not safe.
    no
  3. Write the answer.
    no

Check. Binoculars make the light stronger, so they are dangerous. ✓

Worked example 8.4.2
Look at the table in this section. How many of the actions are safe? Write the number.

Method. Count the rows that say yes.

  1. Read the last column. Wear a hat, stand in the shade, wear sunglasses that block UV light, and look away are safe.
    four yes
  2. Count them. There are four safe actions.
    4
  3. Write the answer.
    4

Check. The other four actions are not safe. ✓

Worked example 8.4.3
Look at the table in this section. Write one action from the table that protects your eyes from the Sun.

Method. Find a row that says yes.

  1. Read the table. Wear a hat with a brim on a sunny day says yes.
    hat
  2. Write one action. Any of the four yes rows is a safe action.
    yes rows
  3. Write the answer.
    Accept any one of the four safe actions in the table.

Check. Any of the safe actions protects your eyes. ✓

Watch out

Watch out: sunglasses do not make it safe to look at the Sun, and binoculars make the Sun even more dangerous.

Try it at home or school (with a grown-up). On a sunny day, with a grown-up, stand with your back to the Sun. Look down at the ground and find your own shadow. You do not need to look at the Sun to know where it is. Wear a hat and sunglasses that block UV light when you are outside on a bright day.

Exam tip

Grown-up tip. Say: “We never look straight at the Sun, because it can hurt our eyes.” If your child looks at the Sun by accident, ask them to look away at once. If their eyes hurt afterwards, see a doctor.

Exercise 8D  Never look directly at the Sun

1
FLook at the picture of the Sun and the eye. Is it safe to look straight at the Sun? Write yes or no.
Never look at the SunLook away. Wear a hat.
2
FLook at the table in this section. Is wearing a hat with a brim safe? Write yes or no.
3
FIf the Sun is very bright, what should you do: look at it, or look away? Write the words.
4
FIs standing in the shade a safe way to protect your eyes from the Sun? Write yes or no.
5
FAre sunglasses a safe way to look at the Sun? Write yes or no.
6
FFill in the gap: never look directly at the ___. Write the word.
7
FTrue or false: a hat with a brim can shade your eyes from the Sun. Write true or false.
8
FTrue or false: a mirror is safe to use to flash sunlight into a friend’s eyes. Write true or false.
9
FLook at the table in this section. How many actions are not safe? Write the number.
10
PSWorking scientifically. Predict what might happen to your eyes if you stare at the Sun for a long time. Write one sentence.
11
RRuby says it is safe to look at the Sun if she wears sunglasses. Is Ruby right? Write no or yes, and give one reason.
8.5

How shadows are formed

Year 3
L4: recognise that shadows are formed when the light from a light source is blocked by an opaque object
Video lesson: How shadows are formedComing soon
Story. Leo has a torch and a teddy. He shines the torch at the teddy, and a dark shape appears on the wall behind it. “Where did that dark shape come from?’ Mei asks. Mr Patel says, “It is a shadow. The teddy blocks the light.”

A shadow is a dark shape that forms when an object blocks the light from a light source. The object that blocks the light is opaque, which means the light cannot pass through it.

To make a shadow you need three things:

The shadow is always on the side of the object that is away from the light source. A clear object lets most of the light through, so it makes a very faint shadow, or none at all.

torchcard(opaque)shadowon the wall
A torch shines on a card. The card blocks the light, so a shadow forms on the wall behind it.
lightWooden blockdark shadowlightClear plastic sheetvery faint shadowlightBalldark shadow
Three objects with the light from the left. The wooden block and the ball make dark shadows. The clear plastic sheet makes a very faint shadow.

The table shows three objects tested with the same torch.

ObjectDoes it block the light?Shadow on the wall
Wooden blockyes, it is opaquedark shadow
Clear plastic sheetno, most light goes throughvery faint shadow
Ballyes, it is opaquedark shadow

Key ideas

  • A shadow is a dark shape that forms when an object blocks light.
  • To make a shadow, you need a light source, an opaque object and a surface.
  • The shadow is on the side of the object away from the light source.
  • A clear object lets most light through, so its shadow is very faint or missing.
Worked example 8.5.1
Look at the table in this section. Which object is opaque and makes a dark shadow: the wooden block or the clear plastic sheet? Write the object.

Method. Find the object that blocks the light.

  1. Read the table. The wooden block blocks the light, and it makes a dark shadow.
    wooden block
  2. Write the object. So the opaque object is the wooden block.
    wooden block
  3. Write the answer.
    wooden block

Check. The clear plastic sheet lets most of the light through. ✓

Worked example 8.5.2
Name the three things you need to make a shadow. Write the three things.

Method. Think about what the shadow needs.

  1. Think about the light. You need a light source to make light.
    light source
  2. Think about the object and the surface. You need an opaque object to block the light, and a surface for the shadow.
    opaque object and surface
  3. Write the answer.
    a light source, an opaque object and a surface

Check. If one of the three is missing, there is no shadow. ✓

Worked example 8.5.3
Look at the table in this section. Which object makes a very faint shadow? Write the object.

Method. Find the row with a very faint shadow.

  1. Read the last column. The clear plastic sheet makes a very faint shadow.
    very faint
  2. Write the object. So the object is the clear plastic sheet.
    clear plastic sheet
  3. Write the answer.
    clear plastic sheet

Check. Most light goes through a clear plastic sheet. ✓

Watch out

Watch out: the shadow is on the side away from the light, never on the side near the light. The shadow is not the object itself.

Try it at home or school (with a grown-up). In a dim room, with a grown-up, shine a torch at a wall. Hold your hand between the torch and the wall, and look at the shadow of your hand. Move your hand closer to the wall, then closer to the torch, and see what happens to the shadow. Switch the torch off when you finish. Never shine a torch into anyone’s eyes.

Exam tip

Grown-up tip. Ask: “What is blocking the light? Where is the shadow: near the torch or away from it?” Let your child use the words opaque, shadow and surface.

Exercise 8E  How shadows are formed

1
FLook at the picture of the torch, the card and the wall. On which side of the card is the shadow: near the torch, or away from the torch? Write the words.
torchcard(opaque)shadowon the wall
2
FWhat is a shadow? Write one short sentence.
3
FWhich object is opaque: the wooden block or the clear plastic sheet? Write the object.
4
FLook at the table in this section. Which object lets most of the light through? Write the object.
5
FLook at the picture of the torch, the card and the wall. What thing gives the light? Write the word.
torchcard(opaque)shadowon the wall
6
FLook at the picture of the torch, the card and the wall. What surface does the shadow fall on? Write the word.
torchcard(opaque)shadowon the wall
7
FFill in the gap: an opaque object ___ light. Write the word.
8
FTrue or false: a shadow can form on the same side of an object as the light source. Write true or false.
9
FTrue or false: a clear plastic sheet makes a dark shadow. Write true or false.
10
PSWorking scientifically. Plan a fair test to compare the shadows of two objects. Write one thing that must stay the same for both objects.
11
RExplain why a wooden block makes a dark shadow, but a clear plastic sheet makes a very faint one. Write one sentence.
8.6

The size and shape of shadows

Year 3
L5: find patterns in the way that the size of shadows change; the shape of a shadow depends on the object and the light
Video lesson: The size and shape of shadowsComing soon
Story. Ruby and Aisha hold a card in front of a torch and a wall. Ruby says, “When I move the torch closer, my shadow gets bigger.” Aisha says, “Let’s measure it, so we know.”

The size of a shadow changes when the distances between the light source, the object and the surface change. We can find patterns by doing a fair test: change only one thing, keep everything else the same, and measure the thing that changes.

In the set-up, the card is 4 cm tall. The shadow height is measured on the wall with a ruler. The picture is not to scale.

card: 4 cm tallwalltorch to cardcard to wall
A torch, a card and a wall. The distance from the torch to the card, and from the card to the wall, are the two distances that change in the fair tests. Not to scale.

Table 1. The card stays 20 cm from the wall. Only the torch distance changes.

Torch to card (cm)Shadow height (cm)
1012
208
406

Table 2. The torch stays 20 cm from the card. Only the wall distance changes.

Card to wall (cm)Shadow height (cm)
106
208
4012
04812shadow height (cm)12 cm10 cm8 cm20 cm6 cm40 cmtorch to card (cm)
A bar chart of the shadow height for each torch distance in Table 1.

The pattern is clear. The closer the torch is to the card, the bigger the shadow. The further the card is from the wall, the bigger the shadow.

The shape of a shadow depends on the shape of the object, and on the way it faces the light. When the light comes from directly above, the shadow looks like the outline of the object seen from above. A ball gives a circle. A box standing on its end gives a square. A box lying on its side gives a rectangle.

lightballshadow: circlelightbox standing on its endshadow: squarelightbox lying on its sideshadow: rectangle
The shadows of a ball, a box standing on its end, and a box lying on its side, with the light from directly above.

Shadows change through the day as the Sun moves. The Sun is low in the sky in the morning and late afternoon, and it is high at midday. Shadows point away from the Sun.

Time of daySun in the skyShadow
Morninglow in the skylong
Middayhigh in the skyshort
Late afternoonlow in the skylong
Morningshadow: longMiddayshadow: shortLate afternoonshadow: long
A stick and the Sun at three times of day. The shadow is long in the morning and late afternoon, and short at midday.

Key ideas

  • A shadow gets bigger when the object is closer to the light source.
  • A shadow gets bigger when the object is further from the surface it falls on.
  • The shape of a shadow depends on the shape of the object and the way it faces the light.
  • Shadows are shortest at midday, when the Sun is highest in the sky.
Worked example 8.6.1
Look at Table 1 in this section. What is the shadow height when the torch is 40 cm from the card? Write the number.

Method. Find the row for 40 cm in Table 1.

  1. Read the row. When the torch is 40 cm from the card, the shadow height is 6 cm.
    6 cm
  2. Write the number. So the shadow height is 6.
    6
  3. Write the answer.
    6

Check. The shadow is smaller when the torch is further away. ✓

Worked example 8.6.2
Look at Table 2 in this section. How much bigger is the shadow when the card is 40 cm from the wall than when it is 10 cm from the wall? Write the number.

Method. Find the two shadow heights in Table 2.

  1. Read the two rows. The shadow is 12 cm when the card is 40 cm from the wall, and 6 cm when it is 10 cm from the wall.
    12 and 6
  2. Subtract. The difference is 12 minus 6, which is 6.
    6
  3. Write the answer.
    6

Check. Check: 6 + 6 = 12. ✓

Watch out. Subtract the smaller shadow from the bigger one.

Worked example 8.6.3
Look at the day table in this section. At which time of day is the shadow shortest? Write the time.

Method. Find the short shadow in the table.

  1. Read the table. The shadow is short at midday, and long in the morning and late afternoon.
    short
  2. Write the time. So the shadow is shortest at midday.
    Midday
  3. Write the answer.
    Midday

Check. The Sun is highest in the sky at midday. ✓

Watch out

Watch out: moving the torch closer to the card makes the shadow bigger, not smaller. Do not change two things at once, or the test is not fair.

Try it at home or school (with a grown-up). With a grown-up, set up a torch, a card and a wall in a dim room. Keep the card 20 cm from the wall, and put the torch 20 cm from the card. Measure the height of the shadow with a ruler. Then move the torch to 40 cm and measure again. Keep everything else the same. Never shine the torch into anyone’s eyes.

Exam tip

Grown-up tip. Ask: “What did you change? What did you keep the same? Which shadow was bigger?” Let your child use the words fair test and shadow height.

Exercise 8F  The size and shape of shadows

1
FLook at Table 1 in this section. What is the shadow height when the torch is 10 cm from the card? Write the number.
2
FLook at Table 2 in this section. What is the shadow height when the card is 20 cm from the wall? Write the number.
3
FLook at the bar chart in this section. Which torch distance gives the smallest shadow? Write the distance in cm.
04812shadow height (cm)12 cm10 cm8 cm20 cm6 cm40 cmtorch to card (cm)
4
FLook at Table 1 in this section. Does the shadow get bigger or smaller as the torch moves further from the card? Write bigger or smaller.
5
FLook at Table 2 in this section. Does the shadow get bigger or smaller as the card moves further from the wall? Write bigger or smaller.
6
FLook at the picture of the shadows of three objects. What shape is the shadow of a ball? Write the shape.
lightballshadow: circlelightbox standing on its endshadow: squarelightbox lying on its sideshadow: rectangle
7
FLook at the picture of the shadows of three objects. What shape is the shadow of a box lying on its side? Write the shape.
lightballshadow: circlelightbox standing on its endshadow: squarelightbox lying on its sideshadow: rectangle
8
FLook at the picture of the day. At which time of day is the shadow shortest? Write the time.
Morningshadow: longMiddayshadow: shortLate afternoonshadow: long
9
FTrue or false: the Sun is highest in the sky at midday, so shadows are usually shortest then. Write true or false.
10
PSWorking scientifically. Ali says the shadow gets bigger when the torch is moved closer to the card. Is Ali right? Write no or yes.
11
RAisha moves the torch and the wall at the same time, and says the test is fair. Why is this not a fair test? Write one sentence.

Chapter summary

SkillMethod
SeeingWe need light to see things. We see an object when light from it enters our eyes. Dark is the absence of light.
Light sourcesA light source makes its own light, such as the Sun, a torch or a lamp. Most things only reflect light.
ReflectionLight bounces off surfaces. A mirror is shiny and reflects light clearly; dull surfaces scatter light.
Safety with the SunNever look directly at the Sun. Look away, wear a hat with a brim, stand in the shade or wear sunglasses that block UV light.
ShadowsA shadow forms when an opaque object blocks light from a light source. It falls on a surface, on the side away from the light.
Size and shape of shadowsThe closer the torch, the bigger the shadow. The further the surface, the bigger the shadow. The shape depends on the object and the light.
Time of dayShadows are shortest at midday, when the Sun is highest in the sky.

Can you…?

  • I can say that we need light to see things, and that dark is the absence of light
  • I can name light sources, and say which things only reflect light
  • I can say that light bounces off shiny surfaces such as mirrors, and that dull surfaces scatter light
  • I can say why we must never look directly at the Sun, and name ways to protect our eyes
  • I can say what a shadow is, and what is needed to make one
  • I can read a fair test on shadow size, and describe the pattern in the results

Key terms

light
the energy that lets us see things
light source
something that makes its own light, such as the Sun, a torch or a lamp
dark
the absence of light, which means there is no light at all
reflect
to bounce light off a surface
reflection
light that bounces off a surface
mirror
a very smooth, shiny surface that reflects light clearly
shadow
a dark shape that forms when an object blocks light from a light source
opaque
an object that light cannot pass through, so it blocks the light and makes a shadow
surface
the outside of an object, or the flat place such as a wall or the ground, where a shadow can fall
UV light
invisible light, found in sunlight, that can harm the eyes and skin
fair test
a test where only one thing is changed, and everything else is kept the same

Exercise 8Z  Check-up

1
Look at the picture of the eyes. In which picture can you see the cup: lights on or lights off? Write the words.
Lights off:no light enters the eyeslampLights on:light enters the eyes
2
Fill in the gap: dark means there is ___ light. Write the word.
3
Which of these is a light source: a book, a torch or a cup? Write the word.
4
Look at the table in section 8.2. How many things are not light sources? Write the number.
5
Which surface makes a clear, bright spot on a wall: a mirror or a black card? Write the surface.
6
What is the name for light that bounces off a surface? Write the word.
7
Is it safe to look at the Sun through binoculars, or safe to wear a hat with a brim? Write the safe action.
8
Name the three things you need to make a shadow. Write the three things.
9
Look at Table 1 in section 8.6. What is the shadow height when the torch is 10 cm from the card? Write the number.
10
Explain why we must never look directly at the Sun. Write one sentence.

Total 17 marks. Allow about 17 minutes.

Exercise 8X  Practice test questions

1
FWrite the word that means there is no light.[1 mark]
2
FIs a torch a light source? Write yes or no.[1 mark]
3
FLook at the picture of six things. Write two light sources from the picture.
SunTorchLampBookChairCup
[2 marks]
4
FLook at the picture of the mirror. Write the word for the light that bounces off the mirror.
torchlight bounces offlight comes inthe mirror
[1 mark]
5
FWhich surface would make the clearest bright spot on a wall: a mirror or a black card? Write the surface.[1 mark]
6
FWrite two safe things you can do to protect your eyes from the Sun.[2 marks]
7
RIs it safe to look at the Sun through binoculars? Write no, and give one reason.[2 marks]
8
FLook at the picture of the torch, the card and the wall. What is the dark shape on the wall called? Write the word.
torchcard(opaque)shadowon the wall
[1 mark]
9
FA class moves a torch away from a card, and measures the shadow on a wall. The card is 4 cm tall. Here are the results.
Torch to card (cm)Shadow height (cm)
1012
208
406

Write the shadow height when the torch is 40 cm from the card. Then say whether the shadow gets bigger or smaller as the torch moves further away.

[3 marks]
10
RLook at the picture of the day. At which time of day is the shadow shortest? Write the time. Then explain in one sentence why it is shortest then.
Morningshadow: longMiddayshadow: shortLate afternoonshadow: long
[3 marks]
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