Year 3 Science: How shadows are formed
Part of the Year 3 Science light and shadows chapter. Chapter overview · whole chapter on one page
How shadows are formed
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:
- a light source, such as a torch;
- an opaque object, such as a wooden block, which blocks the light;
- a surface, such as a wall or the ground, for the shadow to fall on.
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.
The table shows three objects tested with the same torch.
| Object | Does it block the light? | Shadow on the wall |
|---|---|---|
| Wooden block | yes, it is opaque | dark shadow |
| Clear plastic sheet | no, most light goes through | very faint shadow |
| Ball | yes, it is opaque | dark 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.
Method. Find the object that blocks the light.
- Read the table. The wooden block blocks the light, and it makes a dark shadow.wooden block
- Write the object. So the opaque object is the wooden block.wooden block
- Write the answer. wooden block
Check. The clear plastic sheet lets most of the light through. ✓
Method. Think about what the shadow needs.
- Think about the light. You need a light source to make light.light source
- 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
- Write the answer. a light source, an opaque object and a surface
Check. If one of the three is missing, there is no shadow. ✓
Method. Find the row with a very faint shadow.
- Read the last column. The clear plastic sheet makes a very faint shadow.very faint
- Write the object. So the object is the clear plastic sheet.clear plastic sheet
- 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
Method. Look at the picture.
- Read the picture. The card blocks the light, and the shadow is on the wall, behind the card.behind the card
- Decide. The shadow is on the side away from the torch.away from the torch
- Write the answer. away from the torch
Check. The shadow is always away from the light source. ✓
Method. Read the definition in this section.
- Read the definition. A shadow is a dark shape that forms when an object blocks light.blocks light
- Write the answer. Accept any sentence that says a shadow is a dark shape made when an object blocks light.
Check. A shadow needs light, an opaque object and a surface. ✓
Method. Think about which object the light cannot pass through.
- Read the table. The wooden block blocks the light, so it is opaque.opaque
- Write the answer. wooden block
Check. A clear plastic sheet lets most light through. ✓
Method. Read the second row of the table.
- Read the table. The clear plastic sheet does not block most of the light.no
- Write the answer. clear plastic sheet
Check. It makes a very faint shadow. ✓
Method. Look at the picture on the left.
- Read the picture. The torch is labelled, and it sends light towards the card.torch
- Write the answer. torch
Check. The torch is the light source. ✓
Method. Look at the picture on the right.
- Read the picture. The shadow is a dark strip on the wall.wall
- Write the answer. wall
Check. A surface is needed for the shadow to fall on. ✓
Method. Read the definition of opaque.
- Read the definition. An opaque object is one that blocks the light, so light cannot pass through it.blocks
- Write the answer. blocks
Check. The shadow forms where the light is blocked. ✓
Method. Think about where the light is blocked.
- Think about the object. The object blocks the light, so the shadow is on the far side.far side
- Write the answer. false
Check. The shadow is always away from the light source. ✓
Method. Look at the table.
- Read the table. The clear plastic sheet makes a very faint shadow.very faint
- Write the answer. false
Check. Clear objects let most light through. ✓
Method. Think about what makes a test fair.
- Think about the test. Only the object should change; the torch, the distance and the wall must stay the same.stay the same
- Write one thing. For example, the same torch for both objects.same torch
- Write the answer. Accept any one of: the same torch, the same distance from the torch, the same wall.
Check. Only one thing should change in a fair test. ✓
Method. Think about each object.
- Think about the wooden block. The wooden block is opaque, so it blocks the light.blocks the light
- Think about the clear sheet. The clear plastic sheet lets most of the light through.lets light through
- Write the answer. Accept any sentence that says the wooden block blocks the light, but the clear plastic sheet lets most of the light through.
Check. An opaque object makes a shadow; a clear object does not. ✓