Chapter 4 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

S2.6.4 Chapter 4

Opaque, translucent, transparent

Why can I see through glass but not through a wooden door?

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.

By the end you can

  • Sort things as transparent, translucent or opaque
  • Say what light does at each kind of thing
  • Explain how a shadow forms

Light meets many things on its way. Some things let light through. Some do not.

A transparent thing lets almost all light through. Clear glass, clean water and clear plastic are transparent. You can see clearly through them.

A translucent thing lets some light through. It spreads the light out. Paper, thin cloth and frosted glass are translucent. You see a glow, but no clear shapes.

An opaque thing lets no light through. Wood, stone and a book are opaque. You cannot see through them.

Now think of a window and a door. A lamp is on the far side of each. Glass lets the rays reach your eye. A wooden door stops them.

Two pictures. Each has an eye on the left, a pane in the middle and a lamp on the right. In the first, the pane is glass, and an arrow goes from the lamp through it to the eye. In the second, the pane is a wooden door, and the arrow from the lamp stops at the door. Labels: Eye, Glass, Lamp, Door.EyeGlassLampEyeDoorLamp
The rays pass through glass. They stop at the door.

Draw it first

Draw light meeting three sheets

  1. Three rows. In the first row, three rays go straight through a clear sheet. In the second row, the rays go through a cloudy sheet and spread out. In the third row, the rays stop at a solid sheet and a dark patch lies behind it. Labels: transparent, translucent, opaque.transparent

    1 Draw a clear sheet. Draw three rays that go straight through it.

  2. Three rows. In the first row, three rays go straight through a clear sheet. In the second row, the rays go through a cloudy sheet and spread out. In the third row, the rays stop at a solid sheet and a dark patch lies behind it. Labels: transparent, translucent, opaque.transparenttranslucent

    2 Draw a paper sheet. Draw the rays spreading out after it.

  3. Three rows. In the first row, three rays go straight through a clear sheet. In the second row, the rays go through a cloudy sheet and spread out. In the third row, the rays stop at a solid sheet and a dark patch lies behind it. Labels: transparent, translucent, opaque.transparenttranslucentopaque

    3 Draw a thick board. Stop the rays. Shade the dark place behind it.

A shadow forms where an opaque thing blocks light. The light cannot pass. So the place behind the thing is dark.

A torch on the left, an opaque board and a wall on the right. Two rays go from the torch past the top and the bottom of the board. The dark place on the wall between them is the shadow. Labels: Torch, Board, Shadow, Wall.TorchBoardShadowWall
The board blocks the light. The wall behind it is dark.

A transparent thing makes almost no shadow. A translucent thing makes a pale shadow. An opaque thing makes a dark shadow.

See it three ways

As a picture

Three boxes show how much light is behind each thing. Behind glass the box is white, so it is bright. Behind paper the box is dotted, so it is dim. Behind wood the box is black, so it is dark. Labels: Glass, Paper, Wood.GlassPaperWood

In words

Glass is transparent, so it is bright behind it. Paper is translucent, so it is dim. Wood is opaque, so it is dark.

Try it

Which things make shadows?

You need: a torch, a plain wall, a clear plastic bag or cup, a sheet of paper, a book.

Be safe: Never shine a torch into anyone's eyes.

  1. Make the room dim. Shine the torch on the wall.
  2. Hold the clear plastic in the light, near the wall. Look at the wall.
  3. Do the same with the paper. Then do it with the book.
  4. Which makes the darkest shadow? Which makes almost none?

What you will see: The clear plastic makes almost no shadow. The paper makes a pale shadow. The book makes a dark shadow.

If you cannot try it, this is what happens.
Three pictures. Each has a torch on the left, a thing held near a wall on the right, and the patch it leaves on the wall. Light goes on through the clear plastic and the paper, but not through the book. Behind the clear plastic the patch on the wall is white, so there is almost no shadow. Behind the paper the patch is dotted, a pale shadow. Behind the book the patch is black, a dark shadow. Labels: clear plastic, paper, book.clear plasticpaperbook

A wrong idea many people have

If light gets through a thing, you can see through it clearly.

Why it feels right: Clear glass lets light through, and you see clearly through it.

The test that breaks it: Hold a sheet of paper in front of a room lamp. Keep it away from the bulb. You see a glow. Now hold a pencil behind the paper. You see only a blurry shape. Never do this with the Sun.

What is true: Translucent things let light through, but spread it out. You see light, not clear shapes.

Key words

transparent
lets almost all light through. You see clearly through it.
translucent
lets some light through and spreads it out.
opaque
lets no light through.
shadow
a dark place where something blocks the light.

Back to your guess

The answer is A: Glass lets light through. Wood does not.

Glass lets light through, so you see through it. A wooden door blocks the light.

Check yourself

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

  1. Look at the picture. Which row shows a translucent sheet?

    Three rows, A, B and C. In row A the rays stop at a solid sheet. In row B the rays go through a cloudy sheet and spread out. In row C the rays go straight through a clear sheet. Labels: A, B, C.ABC
    Tap your answer.

    1. Not this one. In row A, no light gets through. That is an opaque sheet. Try another.

    2. Yes, that is right. In row B, some light gets through and it spreads out. That is translucent.

    3. Not this one. In row C, the rays go straight through. That is a transparent sheet. Try another.

    See the answer

    B

    In row B, some light gets through and it spreads out. That is translucent.

    • If you chose A: In row A, no light gets through. That is an opaque sheet.
    • If you chose C: In row C, the rays go straight through. That is a transparent sheet.

  2. Which of these is transparent?

    Tap your answer.

    1. Not this one. Wood lets no light through. It is opaque. Try another.

    2. Not this one. Paper lets some light through, but you cannot see clearly. It is translucent. Try another.

    3. Yes, that is right. Clear glass lets almost all light through. You see clearly through it.

    See the answer

    Clear glass

    Clear glass lets almost all light through. You see clearly through it.

    • If you chose A: Wood lets no light through. It is opaque.
    • If you chose B: Paper lets some light through, but you cannot see clearly. It is translucent.

  3. A thin white cloth lets some light through. You cannot see clear shapes through it. What is it?

    Tap your answer.

    1. Yes, that is right. Some light gets through, but it is spread out. That is translucent.

    2. Not this one. A transparent thing lets you see clear shapes. This cloth does not. Try another.

    3. Not this one. An opaque thing lets no light through. This cloth lets some through. Try another.

    See the answer

    Translucent

    Some light gets through, but it is spread out. That is translucent.

    • If you chose B: A transparent thing lets you see clear shapes. This cloth does not.
    • If you chose C: An opaque thing lets no light through. This cloth lets some through.

  4. Why does a book make a dark shadow?

    Tap your answer.

    1. Not this one. If it let light through, the place behind it would be bright. Try another.

    2. Yes, that is right. A book is opaque. The light cannot pass, so the place behind it is dark.

    3. Not this one. A book makes no light. It is not a light source. Go to S2.6.1. Try another.

    See the answer

    It blocks the light.

    A book is opaque. The light cannot pass, so the place behind it is dark.

    • If you chose A: If it let light through, the place behind it would be bright.
    • If you chose C: A book makes no light. It is not a light source. Go to S2.6.1.

  5. From an earlier chapter

    With no light at all, you cannot see your hand. Why?

    Tap your answer.

    1. Not this one. Nothing comes out of your eyes. Light must go into them. Go to S2.6.3. Try another.

    2. Not this one. Waiting does not help. With no light, there is nothing for the eyes to take in. Go to S2.6.3. Try another.

    3. Yes, that is right. We see when light goes into our eyes. With no light, none can reach them.

    See the answer

    There is no light to bounce off my hand into my eyes.

    We see when light goes into our eyes. With no light, none can reach them.

    • If you chose A: Nothing comes out of your eyes. Light must go into them. Go to S2.6.3.
    • If you chose B: Waiting does not help. With no light, there is nothing for the eyes to take in. Go to S2.6.3.

  6. Sort these into transparent, translucent and opaque: clear plastic, paper, wood, stone.

    See the answer

    Transparent: clear plastic. Translucent: paper. Opaque: wood and stone.

    Clear plastic lets almost all light through. Paper lets some through. Wood and stone let none through.

  7. A torch shines on a sheet of paper. A dim glow shows on the wall behind it. Why?

    A torch on the left, a sheet of paper and a wall on the right. One ray goes from the torch to the paper. The wall behind the paper has a dotted patch. Labels: Torch, Paper, dim glow, Wall.TorchPaperdim glowWall
    Tap your answer.

    1. Not this one. Paper makes no light. The glow is torch light that came through. Go to S2.6.1. Try another.

    2. Not this one. Then you would see a clear, bright patch. Paper spreads the light out. Try another.

    3. Not this one. Then the wall behind it would stay dark. Paper lets some light through. Try another.

    4. Yes, that is right. Paper is translucent. Some light gets through and spreads out. So the glow is dim.

    See the answer

    The paper lets some light through.

    Paper is translucent. Some light gets through and spreads out. So the glow is dim.

    • If you chose A: Paper makes no light. The glow is torch light that came through. Go to S2.6.1.
    • If you chose B: Then you would see a clear, bright patch. Paper spreads the light out.
    • If you chose C: Then the wall behind it would stay dark. Paper lets some light through.

Keep it

Copy this into your exercise book.

Transparent things let almost all light through. Translucent things let some through and spread it out. Opaque things let none through, so they make a dark shadow.

Draw: Draw three rows of rays meeting a sheet. Label them transparent, translucent and opaque.

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.