Chapter 3 of 7

All 7 chapters
  1. 1Where light comes from, readunderstood
  2. 2Light goes in straight lines, readunderstood
  3. 3How we see, readunderstood
  4. 4Opaque, translucent, transparent, readunderstood
  5. 5Big and small shadows, readunderstood
  6. 6A shadow stick through the day, readunderstood
  7. 7Mirrors and shiny things, readunderstood

S2.6.3 Chapter 3

How we see

How do I see a cup on the table?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

  • You picked D. Read on. At the end, the chapter comes back to your guess.

By the end you can

  • Say how light lets you see a thing
  • Draw rays going into an eye and never out of it
  • Explain why you see nothing in total darkness

You see a cup on a table. The cup makes no light. A lamp is a light source. It makes its own light.

Rays of light leave the lamp. A ray is one thin line of light. The rays hit the cup. The cup reflects them. To reflect is to send light back. Some rays go into your eyes. Then you see the cup.

Draw it first

Draw how you see a ball

  1. A lamp at the top right, a ball in the middle and an eye at the top left, looking at the ball. An arrow goes from the lamp to the ball. A second arrow goes from the ball into the eye. Labels: Lamp, Ball, Eye.LampBall

    1 Draw a lamp and a ball. Write their names.

  2. A lamp at the top right, a ball in the middle and an eye at the top left, looking at the ball. An arrow goes from the lamp to the ball. A second arrow goes from the ball into the eye. Labels: Lamp, Ball, Eye.LampBall

    2 Draw an arrow from the lamp to the ball.

  3. A lamp at the top right, a ball in the middle and an eye at the top left, looking at the ball. An arrow goes from the lamp to the ball. A second arrow goes from the ball into the eye. Labels: Lamp, Ball, Eye.LampBallEye

    3 Draw an eye. Draw an arrow from the ball into the eye.

In the day, the Sun is the light source. Sunlight bounces off a tree. Some of it goes into your eyes. Then you see the tree.

See it three ways

As a picture

The Sun at the top left, a tree in the middle and an eye at the top right. An arrow goes from the Sun to the tree. A second arrow goes from the tree into the eye. Labels: Sun, Tree, Eye.SunTreeEye

In words

Light leaves a source. It bounces off the thing. It goes into your eye. Then you see the thing.

Look at the arrows. They point into the eye. Eyes take light in. They send no light out.

An eye on the left. Two arrows come into it from the right. One comes from a ball at the top right. One comes from a tree at the bottom right. No arrow leaves the eye. Labels: Eye, Ball, Tree.EyeBallTree
Rays go into the eye. None come out of it.

You see a lamp in a different way. Its own light goes straight into your eye.

An eye on the left and a lamp on the right. One arrow goes straight from the lamp into the eye. Labels: Eye, Lamp.EyeLamp
A lamp makes its own light. The light goes straight into your eye.

With no light at all, no rays reach your eyes. You see nothing.

An eye on the left and a cup on the right. The cup is dotted to show that it is dark. There are no arrows, because there is no light at all. Labels: no light at all, Eye, Cup.no light at allEyeCup
No rays reach the eye. It sees nothing.

Try it

See inside a dark box

You need: a box with a lid, such as a shoe box, a pencil, a white stone, cup or piece of paper.

  1. Push the pencil through one end of the box. Make a small hole.
  2. Put the white thing inside. Shut the lid so that no light gets in.
  3. Put your eye close to the hole. Keep your eye wide open. What do you see?
  4. Lift the lid a little. Look through the hole again.

What you will see: With the lid shut, you see almost nothing. Lift the lid and light comes in. It bounces off the white thing. It goes through the hole into your eye. Now you see it.

If you cannot try it, this is what happens.
Two pictures of a box with a small hole in its left side and an eye looking at the hole. In the first, the lid is shut and the box is dark, with no arrows. In the second, the lid is open a little. An arrow of light goes in through the gap to a ball. Another arrow goes from the ball out through the hole into the eye. Labels: lid shut, lid open a little, Eye, dark.lid shutEyedarklid open a littleEye

A wrong idea many people have

Sight comes out of our eyes.

Why it feels right: Looking feels like your eyes reach out to a thing.

The test that breaks it: Use the box. Your eye is wide open at the hole. If sight came from your eyes, you would see the white thing. With the lid shut, you see almost nothing. In a room with no light, you cannot see your hand. Wide open eyes do not help.

What is true: We see when light goes into our eyes. Eyes only take light in.

Key words

light source
a thing that makes its own light.
ray
one thin line of light.
reflect
to send light back.

Back to your guess

The answer is D: Light bounces off the cup and goes into my eyes.

We see a cup when light bounces off it into our eyes. Nothing comes out of our eyes.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. How do you see a book on a table?

    Tap your answer.

    1. Not this one. Eyes only take light in. They send none out. Think of the dark box. Try another.

    2. Not this one. A book makes no light. It only reflects light from a source. Go to S2.6.1. Try another.

    3. Yes, that is right. A lamp or the Sun lights the book. The book reflects some of that light into your eyes.

    See the answer

    Light bounces off the book and goes into my eyes.

    A lamp or the Sun lights the book. The book reflects some of that light into your eyes.

    • If you chose A: Eyes only take light in. They send none out. Think of the dark box.
    • If you chose B: A book makes no light. It only reflects light from a source. Go to S2.6.1.

  2. You are in a room with no light at all. Your eyes are wide open. Can you see your hand?

    Tap your answer.

    1. Yes, that is right. To see your hand, light must bounce off it into your eyes. In a room with no light, there is none.

    2. Not this one. Nothing comes out of your eyes. With no light to bounce off your hand, you see nothing. Try another.

    3. Not this one. Looking hard does not make light. Without light, you cannot see. Try another.

    See the answer

    No. There is no light to reach my eyes.

    To see your hand, light must bounce off it into your eyes. In a room with no light, there is none.

    • If you chose B: Nothing comes out of your eyes. With no light to bounce off your hand, you see nothing.
    • If you chose C: Looking hard does not make light. Without light, you cannot see.

  3. Look at a picture of seeing. Which way does the arrow at the eye point?

    Tap your answer.

    1. Not this one. The arrow shows which way light goes. Light goes into the eye. Try another.

    2. Yes, that is right. The arrows show the way light travels. It goes from the thing into the eye.

    3. Not this one. Light goes one way only, from the thing into the eye. Try another.

    See the answer

    Into the eye

    The arrows show the way light travels. It goes from the thing into the eye.

    • If you chose A: The arrow shows which way light goes. Light goes into the eye.
    • If you chose C: Light goes one way only, from the thing into the eye.

  4. From an earlier chapter

    A lamp is on. A stiff card with no hole is between lamp and eye. Can you see the lamp?

    Tap your answer.

    1. Not this one. Light goes in straight lines. It does not bend round the card. Go to S2.6.2. Try another.

    2. Not this one. A thin card may let a faint glow through. But you still cannot see the lamp. The card stops the straight rays. Go to S2.6.2. Try another.

    3. Yes, that is right. Light goes in straight lines. The card stops the rays, so none reach your eye.

    See the answer

    No. The card blocks the straight rays.

    Light goes in straight lines. The card stops the rays, so none reach your eye.

    • If you chose A: Light goes in straight lines. It does not bend round the card. Go to S2.6.2.
    • If you chose B: A thin card may let a faint glow through. But you still cannot see the lamp. The card stops the straight rays. Go to S2.6.2.

  5. Draw how you see a cup. Show a lamp, a cup and an eye. Add the arrows.

    See the answer

    One arrow goes from the lamp to the cup. A second arrow goes from the cup into the eye.

    The light goes from the source to the cup. Then it goes into the eye. No arrow leaves the eye.

  6. Joseph looks at a lit candle across a dark room. How does its light reach his eyes?

    Tap your answer.

    1. Not this one. Nothing goes out of his eyes. Eyes only take light in. Try another.

    2. Not this one. A flame makes its own light. Its rays can go straight into an eye. Try another.

    3. Not this one. Light leaves the flame in every direction. Some of it goes into his eyes. Try another.

    4. Yes, that is right. A flame is a light source. Its rays go out in every direction. Some go straight into his eyes.

    See the answer

    The flame's light goes straight into his eyes.

    A flame is a light source. Its rays go out in every direction. Some go straight into his eyes.

    • If you chose A: Nothing goes out of his eyes. Eyes only take light in.
    • If you chose B: A flame makes its own light. Its rays can go straight into an eye.
    • If you chose C: Light leaves the flame in every direction. Some of it goes into his eyes.

  7. In the day, Joseph sees a tree. Which one is the light source?

    Tap your answer.

    1. Yes, that is right. The Sun makes the light. The tree reflects some of it into Joseph's eyes.

    2. Not this one. A tree makes no light. It only reflects sunlight. Go to S2.6.1. Try another.

    3. Not this one. Eyes make no light. They only take light in. Try another.

    See the answer

    The Sun

    The Sun makes the light. The tree reflects some of it into Joseph's eyes.

    • If you chose B: A tree makes no light. It only reflects sunlight. Go to S2.6.1.
    • If you chose C: Eyes make no light. They only take light in.

  8. The lamp lights the ball. Which way does light go so the eye sees the ball?

    A lamp at the top right, a ball in the middle and an eye at the bottom left. Labels: Lamp, Ball, Eye.LampBallEye
    Tap your answer.

    1. Not this one. Eyes take light in. They do not send light out to the ball. Try another.

    2. Not this one. That light shows you the lamp. To see the ball, light must bounce off it into the eye. Try another.

    3. Yes, that is right. The lamp lights the ball. The ball reflects some of that light into the eye. Then you see the ball.

    See the answer

    From the lamp to the ball, then into the eye

    The lamp lights the ball. The ball reflects some of that light into the eye. Then you see the ball.

    • If you chose A: Eyes take light in. They do not send light out to the ball.
    • If you chose B: That light shows you the lamp. To see the ball, light must bounce off it into the eye.

Keep it

Copy this into your exercise book.

We see a thing when light bounces off it into our eyes. Eyes take light in. They send none out. With no light at all, we see nothing.

Draw: Draw a lamp, a ball and an eye. Draw an arrow from the lamp to the ball. Draw one from the ball into the eye.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

No internet tomorrow? Save the whole book as one file (644 KB). It opens on any phone.