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Primary Science · Year 6Chapter 8 · How we see
Year 6 · Chapter 8

How we see

By the end of this chapter you will be able to

  • Sort objects into light sources and objects that reflect light
  • Explain that we see an object because light from it, or reflected from it, enters the eye
  • Describe the path of light from a source to the eye, directly or by reflection
  • Use the rule that the angle of the incoming ray equals the angle of the reflected ray, with a mirror
  • Name the main parts of the eye and say what each one does
  • Describe safe ways to use mirrors and light, and never look at the Sun

You should already know

  • Light travels in straight lines, and light sources and shadows (Chapter 7 of this book)
  • Light and shadows, and how light is blocked (Year 3 Science, Chapter 8)

Where this leads

  • Light in more detail, including refraction and lenses, in later science

National Curriculum for England, Key Stage 2 science, Year 6. Content: L2 use the idea that light travels in straight lines to explain that objects are seen because they give out or reflect light into the eye, L3 explain that we see things because light travels from light sources to our eyes, or from light sources to objects and then to our eyes.

Exercise P  Do you remember?

1
FWhat do we call the dark area behind an object that blocks light? Write the word.
2
FLight travels in what kind of line? Write the word.
3
FWhich material lets light pass through clearly? Write the word: opaque or transparent.
4
FWhat is the name of the light-sensitive organ at the front of the head that we use to see? Write the word.
5
FWhat is a material called if it is shiny and bounces light back? Write the word.
8.1

Light sources and objects that reflect light

Year 6
L2: objects are seen because they give out or reflect light into the eye
Video lesson: Light sources and objects that reflect lightComing soon
Story. In a dark room, Mo switches on a lamp. “Now I can see the book and the pencil,” he says. “But the lamp is the only thing giving out light,” says Priya. “The book and the pencil are reflecting the light from the lamp into our eyes.”

A light source is something that gives out its own light, such as the Sun, a lamp, a torch or a candle.

Most objects do not give out light. We see them because they reflect light from a light source. The reflected light travels into our eyes, and that is how we see the object.

The table sorts six objects.

ObjectLight source or reflects light?
Sunlight source
Moonreflects
Torchlight source
Mirrorreflects
Bookreflects
Candlelight source

Key ideas

  • A light source gives out its own light.
  • Most objects reflect light from a light source.
  • We see an object when light from it, or reflected by it, enters our eyes.
  • The Moon does not give out light; it reflects light from the Sun.
Worked example 8.1.1
Look at the table in section 8.1. Which of the six objects is a light source? Write the names of the light sources.

Method. Read the second column.

  1. Read the column. The objects that say light source are the Sun, the torch and the candle.
    light sources
  2. Write the names. So the light sources are the Sun, the torch and the candle.
    Sun, torch, candle
  3. Write the answer.
    Sun, torch, candle

Check. The Moon, mirror and book reflect light. ✓

Worked example 8.1.2
Why can we see a book in a dark room when the lamp is on? Write the words.

Method. Think about how light reaches the eye.

  1. Think about the source. The lamp is a light source, and it gives out light.
    lamp
  2. Think about the book. The book reflects light from the lamp into our eyes.
    reflects
  3. Write the answer.
    it reflects light from the lamp

Check. The book is not a light source. ✓

Worked example 8.1.3
How many of the six objects reflect light? Write the number.

Method. Count the rows that say reflects.

  1. Count. The Moon, the mirror and the book reflect light.
    three rows
  2. Write the number. So three objects reflect light.
    3
  3. Write the answer.
    3

Check. The other three give out their own light. ✓

Watch out

Watch out: a light source is not the same as a reflector. The Moon is bright in the sky, but it reflects light from the Sun; it is not a light source.

Exam tip

Exam tip. Say whether an object gives out light or reflects it, and then say how the light reaches the eye.

Try it (with your teacher, or a grown-up at home). Look around a room with a grown-up. Find three light sources, and three objects that reflect light. Say how you know which is which, without looking at the Sun or any bright light.

Exercise 8A  Light sources and objects that reflect light

1
FWhich word means something that gives out its own light? Write the words.
2
FIs a torch a light source? Write yes or no.
3
FDoes the book in section 8.1 give out its own light? Write yes or no.
4
FLook at the table in section 8.1. Which object reflects light and is in the Sky? Write the name.
5
FWhat do we call an object that does not give out light but is seen because it reflects light? Write the word.
6
FIs the Sun a light source? Write yes or no.
7
FIn a classroom of 12 objects, 3 give out light and the rest reflect light. How many reflect light? Write the number.
8
PSA class sorted 12 objects. How many more objects reflect light than give out light? Write the number.
9
PSPriya says a mirror gives out its own light. Is Priya right? Write yes or no.
10
PSMo says we see the book because the book gives out light. Is Mo right? Write yes or no.
11
RExplain why we can see the Moon at night, even though it does not give out light. Write one sentence.
12
RExplain why a light source is needed before we can see a reflector. Write one sentence.
13
RChallenge: explain why a dark room looks dark, even though the objects are still there. Write one sentence.
8.2

Reflection with a mirror

Year 6
L2: light reflects off shiny surfaces, and the angle of the incoming ray equals the angle of the reflected ray
Video lesson: Reflection with a mirrorComing soon
Story. Ruby shines a torch at a mirror on the table. The light bounces off the mirror onto the wall. “The light goes in at one angle and out at the same angle,” she says. Her teacher says, “You have found the rule for reflection. Let’s test it.”

A mirror is a smooth, shiny surface that reflects most of the light that hits it. The light that arrives at the mirror is the incoming ray. The light that bounces off is the reflected ray.

The line at right angles to the mirror is called the normal. The incoming ray and the reflected ray make equal angles with the normal.

normalincoming rayreflected raythe angles on each side of the normal are equal
A mirror with an incoming ray and a reflected ray. Both rays make the same angle with the normal line.

Ruby tested three rays on a mirror and recorded the angles measured from the normal.

RayAngle of the incoming ray (degrees)Angle of the reflected ray (degrees)
Ray a3030
Ray b4545
Ray c6060

Key ideas

  • A mirror reflects light.
  • The incoming ray and the reflected ray make equal angles with the normal.
  • The normal is a line at right angles to the mirror.
  • A mirror reflects light that hits it, so it can send light into your eyes.
Worked example 8.2.1
Look at the table in section 8.2. For Ray a, what is the angle of the reflected ray? Write the number of degrees.

Method. Read the row for Ray a.

  1. Read the row. The incoming angle for Ray a is 30 degrees.
    30
  2. Use the rule. The reflected angle is equal to the incoming angle.
    30 degrees
  3. Write the answer.
    30 degrees

Check. The two angles are equal, so the rule holds. ✓

Worked example 8.2.2
For Ray b, the incoming angle is 45 degrees. What is the angle of the reflected ray? Write the number of degrees.

Method. Use the rule for reflection.

  1. Read the rule. The reflected angle equals the incoming angle.
    equal
  2. Apply the rule. The reflected angle is 45 degrees.
    45 degrees
  3. Write the answer.
    45 degrees

Check. Ray b was measured as 45 degrees on both sides. ✓

Worked example 8.2.3
What is the total of all the incoming and reflected angles in the table? Write the number of degrees.

Method. Add all six angles.

  1. Add the incoming angles. The incoming angles are 30, 45 and 60.
    30 + 45 + 60 = 135
  2. Add the reflected angles. The reflected angles are also 30, 45 and 60, so the total is 135 + 135.
    135 + 135 = 270
  3. Write the answer.
    270 degrees

Check. Each pair is equal, so the total is twice 135. ✓

Watch out

Watch out: the angles are measured from the normal, not from the mirror. A ray that hits the mirror at 30 degrees to the surface is 60 degrees from the normal.

Exam tip

Exam tip. Measure the angles from the normal line, and say that the reflected angle is equal to the incoming angle.

Try it (with your teacher, or a grown-up at home). In a dim room, with a grown-up, shine a torch at a small mirror laid flat on a table. Do not shine the torch or the reflection into anyone's eyes. Hold a card at the angle the light bounces. Measure the angle on each side of a line drawn at right angles to the mirror.

Exercise 8B  Reflection with a mirror

1
FWhat do we call the line at right angles to a mirror, used to measure the angles? Write the word.
2
FWhat do we call the light that hits a mirror? Write the words.
3
FWhat do we call the light that bounces off a mirror? Write the words.
4
FLook at the table in section 8.2. What is the reflected angle for Ray c? Write the number of degrees.
5
FIs the reflected angle always equal to the incoming angle, in the table? Write yes or no.
6
FWhat is a smooth, shiny surface that reflects most of the light that hits it? Write the word.
7
FRay b has an incoming angle of 45 degrees. What is its reflected angle? Write the number of degrees.
8
PSAdd the angles of Ray a: the incoming angle and the reflected angle. Write the number of degrees.
9
PSA ray hits a mirror, with an incoming angle of 25 degrees measured from the normal. What is the reflected angle? Write the number of degrees.
10
PSPriya says the reflected angle is always bigger than the incoming angle. Is Priya right? Write yes or no.
11
RExplain why a mirror makes it possible to see a torch beam bouncing off it. Write one sentence.
12
RExplain why the normal is needed when we measure the angles of rays. Write one sentence.
13
RChallenge: explain why a mirror placed at a steeper angle sends the reflected light in a different direction. Write one sentence.
8.3

Light from the source to our eyes

Year 6
L3: light travels from light sources to our eyes, or from light sources to objects and then to our eyes
Video lesson: Light from the source to our eyesComing soon
Story. Aisha looks at a candle on the table. “The light goes straight from the candle into my eyes,” she says. Then she looks at a book lit by a lamp. “Here the light goes from the lamp to the book, and then into my eyes,” says Mr Patel. “There are two paths.”

We see things because light travels from a light source to our eyes. There are two ways this can happen:

candleeyelight source straight to the eyelampbookeyelight bounces
Two paths: light from a candle goes straight to the eye, and light from a lamp reflects off a book and then goes to the eye.

The table shows three things we see, and how the light reaches our eyes.

Thing seenPath of the light to the eye
A candlestraight to the eye
A bookfrom a lamp, to the book, then to the eye
The moonfrom the Sun, to the Moon, then to the eye

Key ideas

  • Light from a source can go straight to the eye.
  • Light can also go from a source, to an object, and then to the eye.
  • The reflected light is the light that bounces off the object.
  • The eye needs light to reach it, from the source directly or by reflection.
Worked example 8.3.1
Look at the table in section 8.3. How does light from the candle reach the eye? Write the words.

Method. Read the first row.

  1. Read the row. Light from the candle goes straight to the eye.
    straight
  2. Write the words. So the path is straight to the eye.
    straight to the eye
  3. Write the answer.
    straight to the eye

Check. The candle is a light source. ✓

Worked example 8.3.2
How does light from the lamp reach the eye, when we look at a book? Write the path in words.

Method. Read the second row.

  1. Read the row. Light goes from the lamp to the book, then to the eye.
    lamp to book
  2. Write the path. So the path is from the lamp, to the book, then to the eye.
    lamp, book, eye
  3. Write the answer.
    from the lamp, to the book, then to the eye

Check. The book reflects the light. ✓

Worked example 8.3.3
In the Moon row, what is the light source? Write the word.

Method. Read the third row.

  1. Read the row. The light goes from the Sun, to the Moon, then to the eye.
    Sun
  2. Write the word. So the light source is the Sun.
    Sun
  3. Write the answer.
    Sun

Check. The Moon reflects sunlight into our eyes. ✓

Watch out

Watch out: the light path to the eye always starts at a light source. A book is not a light source, so light reaches the book from a source first.

Exam tip

Exam tip. Write a light path as: source, then object (if any), then eye.

Try it (with your teacher, or a grown-up at home). In a dim room, with a grown-up, look at a candle or a lamp directly, then look at a book lit by the same lamp. Write both light paths in arrows, as source, object, eye. Keep the candle away from curtains and hair.

Exercise 8C  Light from the source to our eyes

1
FWhat is the path of light from a candle to our eyes? Write the words.
2
FIn the table in section 8.3, which object reflects light before it reaches the eye? Write the name.
3
FWhich light source starts the path of light to our eyes when we see the Moon? Write the name.
4
FDoes light need to travel from a source to the eye for us to see an object? Write yes or no.
5
FWrite the path of light for a book that is lit by a lamp, in arrows, starting from the lamp. Write the path in words.
6
FIs the book a light source? Write yes or no.
7
FHow many light paths are shown in the table in section 8.3? Write the number.
8
PSPriya says the light from a candle reaches the eye by reflection off a book. Is Priya right? Write yes or no.
9
PSMo says we can see the Moon because the Moon gives out light. Is Mo right? Write yes or no.
10
PSWrite the source, object and eye in order, for a book lit by a torch. Write the three words.
11
RExplain why light from a candle needs no reflection to reach the eye. Write one sentence.
12
RExplain why a book can be seen in a room with a lamp, when the book does not give out light. Write one sentence.
13
RChallenge: explain why the Moon can be seen in a dark sky, even though it is far from the Earth. Write one sentence.
8.4

How the eye works

Year 6
L3: light travels from light sources to our eyes; the eye receives the light and sends signals to the brain
Video lesson: How the eye worksComing soon
Story. Sam closes his eyes in a dark room, then opens them under a bright lamp. “The middle of my eye got smaller,” he says. The nurse explains: “The opening that lets in light, called the pupil, gets smaller in bright light and bigger in dim light.”

The eye is an organ that receives light. Light enters the eye through the pupil, which is the opening in the middle. The lens focuses the light onto the retina at the back of the eye. The retina has light-sensitive cells, which send signals along the optic nerve to the brain. The brain then interprets the signals, so we see the object.

brainpupillensretinaoptic nervelight enters at the pupil, the lens focuses it on the retina
A simple diagram of the eye. Light enters at the pupil, the lens focuses it on the retina at the back, and the optic nerve carries signals to the brain.

The table names the main parts of the eye.

Part of the eyeWhat it does
Pupilthe opening that light enters the eye through; it gets smaller in bright light
Lensfocuses the light onto the back of the eye
Retinathe layer at the back of the eye, with light-sensitive cells
Optic nervecarries signals from the retina to the brain

Key ideas

  • Light enters the eye through the pupil.
  • The lens focuses the light onto the retina.
  • The retina sends signals along the optic nerve to the brain.
  • The pupil gets smaller in bright light and bigger in dim light.
Worked example 8.4.1
Which part of the eye focuses the light onto the back of the eye? Write the word.

Method. Read the table.

  1. Read the table. The lens focuses the light onto the retina.
    lens
  2. Write the word. So the part is the lens.
    lens
  3. Write the answer.
    lens

Check. The lens works like the lens in a camera. ✓

Worked example 8.4.2
Which part of the eye carries signals from the retina to the brain? Write the words.

Method. Read the table.

  1. Read the table. The optic nerve carries signals from the retina to the brain.
    optic nerve
  2. Write the words. So the part is the optic nerve.
    optic nerve
  3. Write the answer.
    optic nerve

Check. The brain then tells us what we see. ✓

Worked example 8.4.3
In bright light, does the pupil get bigger or smaller? Write the word.

Method. Read the description.

  1. Read the description. The pupil gets smaller in bright light.
    smaller
  2. Write the word. So the pupil gets smaller.
    smaller
  3. Write the answer.
    smaller

Check. A smaller pupil lets less light in. ✓

Watch out

Watch out: the eye does not send light to the brain. Light enters the eye, and the retina sends signals to the brain.

Exam tip

Exam tip. Name the eye part and say what it does: pupil lets light in, lens focuses it, retina senses it, optic nerve carries signals.

Try it (with your teacher, or a grown-up at home). Look at your eyes in a mirror in a dim room, then in a brighter room, with a grown-up. Notice whether the dark centre gets bigger or smaller. Do not look at a bright light for a long time, and never look at the Sun.

Exercise 8D  How the eye works

1
FWhich part of the eye is the opening that lets light in? Write the word.
2
FWhat is the job of the lens in the eye? Write the words.
3
FWhich part of the eye is the layer at the back that has light-sensitive cells? Write the word.
4
FWhich nerve carries signals from the retina to the brain? Write the words.
5
FWhere does the light go after it passes through the lens? Write the word.
6
FIn dim light, is the pupil bigger or smaller? Write the word.
7
FDoes the eye send light to the brain? Write yes or no.
8
PSAli says the pupil is the part of the eye that focuses light. Is Ali right? Write yes or no.
9
PSSam goes from a dark room into bright light. Does his pupil get smaller or bigger? Write the word.
10
PSName the two parts of the eye that light passes through, in order, from the front. Write the two words.
11
RExplain why the lens is needed to make the image on the retina clear. Write one sentence.
12
RExplain why we can see things in a dim room, but not clearly in the dark. Write one sentence.
13
RChallenge: explain why the pupil getting smaller in bright light protects the retina. Write one sentence.
8.5

Safety with light and mirrors

Year 6
L2 and L3: safe use of light sources and mirrors, including the Sun
Video lesson: Safety with light and mirrorsComing soon
Story. On a sunny day, Tom uses a small mirror to send a bright spot of sunlight across the playground. “Look, the light is dancing on the wall!” he says. Mrs Chen stops him. “Never reflect sunlight into anyone’s eyes. Sunlight is very strong, and it can damage the eyes.”

The Sun is a very bright light source. Its light is very strong, and it can damage the eyes if we look at the Sun directly.

A mirror can reflect sunlight, so it can send a strong beam into someone's eyes. This is just as dangerous as looking at the Sun itself. Mirrors must never be used to reflect sunlight into anyone's eyes, or onto a person's face.

The table gives safety rules for light and mirrors.

RuleWhy it matters
Never look at the Sunthe Sun can damage the eyes, even for a short time
Never use a mirror to reflect sunlight into anyone's eyesa reflected beam is still very strong and can cause harm
Use a torch and a mirror only in a dim room, with a grown-upthe light is easier to control, and it is safer
Keep torch beams and mirrors away from facesbright light can hurt the eyes

Key ideas

  • Never look at the Sun, directly or through a mirror or a telescope.
  • A mirror can reflect sunlight, so never angle it into someone's eyes.
  • Use torches and mirrors safely, in a dim room, with a grown-up.
  • Keep bright light away from faces and eyes.
Worked example 8.5.1
Is it safe to reflect sunlight with a mirror into someone's eyes? Write yes or no.

Method. Check the safety rule.

  1. Read the rule. The table says never use a mirror to reflect sunlight into anyone's eyes.
    never
  2. Decide. So it is not safe, and the answer is no.
    no
  3. Write the answer.
    no

Check. Reflected sunlight is still strong. ✓

Worked example 8.5.2
Name one rule that keeps a torch beam safe. Write the words.

Method. Read the table.

  1. Read the table. Keep torch beams and mirrors away from faces.
    away from faces
  2. Write the words. So one rule is to keep torch beams away from faces.
    away from faces
  3. Write the answer.
    keep torch beams away from faces

Check. The bright beam can hurt the eyes. ✓

Worked example 8.5.3
Is it safe to look at the Sun through a mirror? Write yes or no.

Method. Check the rule.

  1. Read the rule. The rule says never look at the Sun, directly or through a mirror.
    never
  2. Decide. So the answer is no.
    no
  3. Write the answer.
    no

Check. Mirrors do not make the Sun safe. ✓

Watch out

Watch out: a mirror does not make sunlight weaker. It reflects the same strong light, so it can cause harm if it is aimed at an eye.

Exam tip

Exam tip. When you write about safety with light, name the source, the risk, and the rule.

Try it (with your teacher, or a grown-up at home). With a grown-up, shine a torch at a mirror in a dim room, and watch the reflected spot on a wall. Keep the beam and the spot away from all faces and eyes. Turn the torch off before you leave the mirror.

Exercise 8E  Safety with light and mirrors

1
FIs it safe to look directly at the Sun? Write yes or no.
2
FCan a mirror reflect sunlight strongly enough to harm an eye? Write yes or no.
3
FWhere should a torch beam be kept, to be safe? Write the word: away from eyes or at eyes.
4
FShould a mirror be used to reflect sunlight onto a person's face? Write yes or no.
5
FIs it safe to look at the Sun through a mirror? Write yes or no.
6
FIn which room should torches and mirrors be used, according to the table in section 8.5? Write the word.
7
PSPriya uses a mirror in the sun to make a spot on the wall, away from everyone's eyes. Is this safe? Write yes or no.
8
PSTom says a mirror makes sunlight weaker, so it is safe to aim it at a face. Is Tom right? Write yes or no.
9
PSName one safety rule that is also about the Sun and the eyes. Write one sentence.
10
RExplain why a mirror reflecting sunlight is as dangerous as looking at the Sun. Write one sentence.
11
RChallenge: explain why we should always turn off a torch before leaving a mirror. Write one sentence.

Chapter summary

SkillMethod
Light sourcesA light source gives out its own light. Most objects are seen because they reflect light.
ReflectionA mirror reflects light. The incoming ray and the reflected ray make equal angles with the normal.
Paths to the eyeLight goes from a source straight to the eye, or from a source to an object, then to the eye.
The eyeLight enters the pupil, the lens focuses it on the retina, and the optic nerve carries signals to the brain.
SafetyNever look at the Sun, and never reflect sunlight into anyone's eyes with a mirror.

Can you…?

  • I can sort objects into light sources and reflectors
  • I can describe the two paths of light from a source to the eye
  • I can use the rule that the reflected angle equals the incoming angle
  • I can name the main parts of the eye and what each one does
  • I can describe safe rules for light and mirrors, and never look at the Sun

Key terms

light source
an object that gives out its own light, such as the Sun, a lamp or a candle
reflect
to bounce light off a surface
reflector
an object that reflects light from a source, such as a book or the Moon
mirror
a smooth, shiny surface that reflects most of the light that hits it
normal
the line at right angles to a mirror, from which angles are measured
incoming ray
the light that arrives at a mirror or surface
reflected ray
the light that bounces off a mirror or surface
pupil
the opening in the eye that light enters through
lens
the part of the eye that focuses light onto the retina
retina
the layer at the back of the eye, with light-sensitive cells
optic nerve
the nerve that carries signals from the retina to the brain

Exercise 8Z  Check-up

1
Which of these is a light source: a book or a candle? Write the word.
2
What do we call the light that bounces off a mirror? Write the words.
3
Look at the table in section 8.2. What is the reflected angle for Ray a? Write the number of degrees.
4
What path does the light take from a candle to the eye? Write the words.
5
What path does the light take from a lamp to our eyes when we see a book? Write the words.
6
Which part of the eye carries signals to the brain? Write the words.
7
Which part of the eye focuses the light onto the retina? Write the word.
8
In a dim room, does the pupil get bigger or smaller? Write the word.
9
In the classroom sort in section 8.1, 3 of 12 objects give out light. How many objects reflect light? Write the number.
10
Explain why a mirror can send light into a person's eyes. Write one sentence.

Total 16 marks. Allow about 16 minutes.

Exercise 8X  Practice test questions

1
FName a light source from this list: book, Moon, candle. Write the word.[1 mark]
2
RExplain why we can see a book in a room that has a lamp on. Write one sentence.[2 marks]
3
FA ray of light hits a mirror at an angle of 45 degrees from the normal. Write the angle of the reflected ray, in degrees.[1 mark]
4
PSUsing the mirror table in section 8.2, write the total of all six angles, in degrees.[2 marks]
5
RA student says: “We see the Moon because it gives out its own light.” Explain why this is not correct. Write one sentence.[2 marks]
6
FWrite the path of light from a candle to the eye. Write the words.[1 mark]
7
FName the part of the eye that carries signals from the retina to the brain. Write the words.[1 mark]
8
RExplain why the pupil gets smaller in bright light. Write one sentence.[2 marks]
9
PSWrite one safety rule for using a mirror with sunlight. Write one sentence.[2 marks]
10
PSIn a classroom sort, 3 objects give out light and 9 reflect light. What fraction of the 12 objects give out light? Write the fraction.[2 marks]
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