Year 6 Science: Shadow size and distance
Part of the Year 6 Science light travels in straight lines chapter. Chapter overview · whole chapter on one page
Shadow size and distance
The size of a shadow depends on how far the object is from the light. The light travels in straight lines from the torch, past the edges of the object, and spreads out. When the object is nearer the light, the light spreads more, so the shadow is bigger.
When the object is further from the light, the shadow is smaller.
Tom measured the height of the shadow for four distances. The distances are from the torch to the card, in centimetres.
| Distance from the torch (cm) | Shadow height (cm) |
|---|---|
| 20 | 30 |
| 40 | 15 |
| 60 | 10 |
| 120 | 5 |
Key ideas
- A nearer object makes a bigger shadow.
- A further object makes a smaller shadow.
- The shape of the shadow stays the same as the object, but its size changes.
- Light travels in straight lines, so the light spreads out and the shadow changes size.
Method. Read the row for 20 cm.
- Find the row. The row for a distance of 20 cm gives a shadow height.20 cm
- Write the height. The shadow height is 30 cm.30 cm
- Write the answer. 30 cm
Check. The nearest card made the biggest shadow. ✓
Method. Subtract the two shadow heights.
- Read the heights. At 40 cm the shadow is 15 cm, and at 60 cm it is 10 cm.15 and 10
- Subtract. The change is 15 minus 10.15 - 10 = 5
- Write the answer. 5 cm
Check. 10 + 5 = 15. ✓
Method. Find the smallest shadow height.
- Read the heights. The smallest shadow is 5 cm.5 cm
- Write the distance. This shadow is at a distance of 120 cm.120 cm
- Write the answer. 120 cm
Check. The furthest card made the smallest shadow. ✓
Watch out
Watch out: the shadow does not get smaller in the same way as the distance grows. Read the table carefully: the height changes faster when the card is near the torch.
Exam tip
Exam tip. Say that a nearer object makes a bigger shadow, and give a number from the table as evidence.
Try it (with your teacher, or a grown-up at home). With a grown-up, hold a card shape close to a wall and shine a torch on it. Move the card slowly away from the wall, then nearer, and note the size of the shadow. Do the test with the torch at the same distance from the wall each time, and keep the same card.
Exercise 7C Shadow size and distance
Method. Read the row for 60 cm.
- Find the row. The row for 60 cm gives a shadow height.60 cm
- Write the height. The shadow is 10 cm tall.10 cm
- Write the answer. 10 cm
Check. 10 is smaller than 15 and 30. ✓
Method. Read the row for 40 cm.
- Find the row. The row for 40 cm gives a shadow height.40 cm
- Write the height. The shadow is 15 cm tall.15 cm
- Write the answer. 15 cm
Check. The shadow at 40 cm is between 30 and 10. ✓
Method. Find the biggest shadow.
- Read the heights. The biggest shadow is 30 cm.30 cm
- Write the distance. That shadow is made at 20 cm from the torch.20 cm
- Write the answer. 20 cm
Check. The nearest card gives the largest shadow. ✓
Method. Find the smallest shadow.
- Read the heights. The smallest shadow is 5 cm.5 cm
- Write the distance. That shadow is made at 120 cm from the torch.120 cm
- Write the answer. 120 cm
Check. The furthest card gives the smallest shadow. ✓
Method. Read the table.
- Read the table. At 20 cm the shadow is 30 cm, and at 120 cm it is 5 cm.nearer, bigger
- Decide. So nearer objects make bigger shadows, and the answer is yes.yes
- Write the answer. yes
Check. The table shows the pattern. ✓
Method. Subtract the two shadow heights.
- Read the heights. At 20 cm the shadow is 30 cm, and at 40 cm it is 15 cm.30 and 15
- Subtract. The difference is 30 minus 15.30 - 15 = 15
- Write the answer. 15 cm
Check. 15 + 15 = 30. ✓
Method. Find the 15 in the table.
- Read the table. The shadow height of 15 cm is at 40 cm from the torch.40 cm
- Write the distance. So the distance is 40 cm.40 cm
- Write the answer. 40 cm
Check. A shadow of 15 cm is at 40 cm. ✓
Method. Think about the shape and the size.
- Think about the shape. The shape comes from the object, so it stays the same.stays the same
- Decide. Only the size changes, so the answer is no.no
- Write the answer. no
Check. Moving the card changes the size, not the shape. ✓
Method. Compare the heights.
- Read the heights. At 120 cm the shadow is 5 cm, and at 20 cm it is 30 cm.5 and 30
- Decide. So Ali is not right.no
- Write the answer. no
Check. The shadow at 20 cm is six times the height of the one at 120 cm. ✓
Method. Use the pattern from the table.
- Find the product. In every row, the distance times the shadow height is 600, so 60 x 10 = 600.600
- Divide. At 30 cm the shadow is 600 divided by 30.600 / 30 = 20
- Write the answer. 20 cm
Check. The pattern only holds as shown in the table. ✓
Method. Think about how light spreads.
- Think about the light. Light travels in straight lines from the torch, and spreads out with distance.spreads out
- Think about the object. A nearer object blocks a wider spread of light, so its shadow is bigger.bigger
- Write the answer. Accept any sentence that says light travels in straight lines and spreads out from the torch, so a nearer object blocks more of it and makes a bigger shadow.
Check. The shadow is bigger because the edges are at wider angles. ✓
Method. Check the table.
- Read the table. The table shows that the shadow is smaller when the card is further from the torch.smaller
- Decide. So Tom is not right.no
- Write the answer. no
Check. Nearer means bigger in this table. ✓
Method. Plan the test.
- Choose the change. Change only the distance of the card from the torch.distance
- Keep the same. Keep the torch, the card and the wall the same each time.same
- Write the answer. Accept any answer that says keep the torch, the card and the wall the same, and change only the distance.
Check. Only one variable changes in a fair test. ✓