Year 6 science · Key Stage 2 · Light
Year 6 light: how light travels, how we see and shadows
In Year 6, children learn that light travels in straight lines and use that idea to explain how we see things and why shadows are shaped as they are. They find out that we see an object because light from it, either given out or reflected, enters our eyes. It builds on Year 3 work on light sources, reflection and shadows, and gives children a way to explain and predict what they see.
How light travels and how we see, explained
The central idea is that light appears to travel in straight lines. Children test it with a torch and a row of cards with holes in them: the beam passes through only when the holes are lined up in a straight row. They draw light as straight lines with arrowheads, using a ruler, to show its path. Light travels very fast, so it seems instant.
The second idea is how we see. Some objects are light sources, such as the Sun, a lamp, a candle flame or a screen. They give out their own light, and we see them when that light travels into our eyes. Most things we see are not light sources. A book, a tree or the Moon is seen because light from a source hits it, bounces off (is reflected) and then goes into our eyes. Without light there is nothing to see: in a completely dark room we see nothing, and our eyes do not send out anything that lets us see. Children explain this with diagrams that show light going from the source to the object to the eye. Looking at a very bright light source, particularly the Sun, can damage the eyes, so children are always told never to look straight at it.
Shadows are the third idea. A shadow forms when an opaque object blocks light. Because light travels in straight lines, the light that would have passed through the object’s place is stopped, leaving a dark area with the same outline as the object. That is why a shadow puppet’s shadow has the same shape as the puppet. With the wall or screen kept in the same place, moving the object closer to the light source makes the shadow larger, and moving it away makes it smaller. Transparent materials let light through and make hardly any shadow, translucent ones make a faint one, and opaque ones make a dark one.
Children use these ideas to predict and explain. A periscope uses two mirrors to turn light round corners in straight sections. A car’s rear-view mirror is placed so that light from behind reaches the driver’s eyes. Schools might also look at rainbows, the colours of soap bubbles, how objects look bent in water and coloured filters. Children can talk about what happens, but don’t have to explain these things.
Words your child will hear
- Light source
- Something that gives out its own light, such as the Sun, a torch or a candle.
- Reflect
- To bounce off a surface. We see most objects because they reflect light into our eyes.
- Ray
- A straight line with an arrow, drawn to show the path of light.
- Opaque
- Does not let any light through, and so makes a dark shadow.
- Transparent
- Lets light through so you can see clearly through it, like clear glass.
- Translucent
- Lets some light through but you cannot see clearly through it, like tracing paper.
- Periscope
- A tube with mirrors that lets you see over or around something.
What the National Curriculum says
In Year 6, pupils should be taught to:
- Recognise that light appears to travel in straight lines
- 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
- 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
- Use the idea that light travels in straight lines to explain why shadows have the same shape as the objects that cast them
Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.
A worked example
A lamp is on in a room with a book on the table. Explain, with a diagram, how you can see the book and why a pencil placed in front of the lamp makes a shadow.
- Identify the light source and the object. The lamp is the light source, as it gives out its own light. The book is not a light source, so we only see it because it reflects light.
- Draw the light from the lamp to the book. Use a ruler to draw straight lines with arrowheads pointing from the lamp to the book, because light travels in straight lines.
- Draw the light from the book to the eye. Draw more straight lines with arrowheads from the book into the eye. The arrows point towards the eye, since the light goes into the eye.
- Explain: the lamp gives out light, the book reflects some of it, and the reflected light enters the eye, so we see the book.
- Add the pencil between the lamp and a wall. Light travels in straight lines and the pencil is opaque, so it blocks the rays that hit it. Light continues past each side, and the wall behind the pencil is dark in the shape of the pencil.
We see the book because light from the lamp reflects off it and travels in straight lines into our eyes. The pencil makes a shadow with the same shape as the pencil because it blocks the straight rays of light that would have reached the wall behind it.
Common mistakes and how to help
Thinking we see because light comes out of our eyes
Looking feels like an active thing we do, and cartoons often show rays leaving the eyes.
What helps: Ask why we can’t see in a completely dark room even with our eyes wide open. Arrows on diagrams should always point into the eye.
Thinking the Moon, or any shiny object, is a light source
The Moon looks bright and glowing in a dark sky.
What helps: A light source makes its own light. Ask what the Moon would look like if the Sun were switched off. We see it because it reflects sunlight.
Thinking only shiny things reflect light
Mirrors are the obvious example of reflection, so children assume a book or a wall does not reflect.
What helps: Explain that nearly everything reflects light, and that is how we see it. Shiny, smooth surfaces such as mirrors give clear images, while rough surfaces scatter the light in many directions.
Believing a shadow gets bigger when the object moves away from the light
It seems natural that something further away is bigger or darker.
What helps: Move a toy towards and away from a torch against a wall. The shadow is biggest when the object is close to the light source and smallest when it is far away.
How to help at home
- Straight line test. Make a hole in the same place in three pieces of card, stand them in a row and shine a torch through. Slide one card sideways and watch the light stop. Don’t shine torches at anyone’s eyes.
- Shadow puppets. Make a shadow puppet with card and a stick, and shine a torch on it against a wall. Find out how to make the shadow larger and smaller, and notice that its shape always matches the puppet.
- Dark box. Put a small toy in a shoebox with a lid and a small peephole. Look through the hole, then ask an adult to cut a second hole for a torch to shine in from the side. You can only see the toy when light gets in and reflects out.
- Make a periscope. Use a long cardboard box or a clean juice carton and two small flat mirrors (plastic ones are safest), one near each end. Set both at 45 degrees and parallel to each other, so the top one faces down the tube and the bottom one faces up it. Cutting the windows is a job for an adult. The periscope lets your child peek over the back of a sofa, and they can trace the light’s straight path from mirror to mirror.
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