Primary 4 Science
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Key Concepts Covered
- How shadows are formed — light source, opaque/translucent object, screen
- Shadow darkness — opaque vs translucent objects
- Shadow size — distance between torch and object; distance between object and screen
- Shadow length during the day — Sun position at morning, noon, evening
- Shadow shape — how it depends on the side of the object facing the light source
Multiple Choice Questions
[2 marks each · 20 marks]Structured Questions
[10 marks each · 40 marks]Explain how shadows are formed.
Ravi carried out an investigation to find out how the distance between a torch and an object affects the size of the shadow formed on a screen. He kept the distance between the object and the screen constant.
| Distance from torch to object (cm) | Shadow size |
|---|---|
| 5 | Very large |
| 10 | Large |
| 20 | Medium |
| 30 | Small |
The diagram below shows the position of the Sun at three different times of the day. A tree stands in an open field.
| Morning | Noon | Evening |
|---|---|---|
Sarah placed three different materials between a torch and a screen, one at a time. She observed the shadow formed on each occasion.
| Material | Type | Observation |
|---|---|---|
| A — Cardboard | Opaque | A dark and clear shadow was formed |
| B — Frosted glass | Translucent | A faint and lighter shadow was formed |
| C — Clear glass | Transparent | No shadow was formed |
Answer Key
Section A — Multiple Choice
Section B — Structured Questions
(a) Three things needed to form a shadow:
- A light source (e.g., torch, Sun) that gives off light.
- An opaque or translucent object that blocks some or all of the light travelling in straight lines.
- A surface/screen on which the shadow is formed.
(b) A shadow is dark because the opaque object blocks light from reaching that area. The part of the screen behind the object does not receive light, so it appears darker than the surrounding areas where light reaches.
(c) A transparent object allows most of the light to pass through it, so no shadow is formed because light still reaches the screen.
(a) The further the object is from the torch, the smaller the shadow. (OR: The closer the object is to the torch, the larger the shadow.)
(b) If Ravi moved the object closer to the screen, the shadow would become smaller. This is because when the object is closer to the screen, less area of the screen is blocked from receiving light.
(c) Two variables to keep constant: (1) The distance between the object and the screen; (2) The same torch/light source used each time. (Also acceptable: the same object used each time.)
(a) The shadow is shortest at noon because the Sun is directly overhead, so the tree blocks light in a small area directly beneath it.
(b) The shadow is longest at sunset (and sunrise) because the Sun is near the horizon and its rays hit the tree at a low angle, causing the shadow to stretch out further across the ground.
(c) In the morning, the shadow points West (opposite to where the Sun rises in the East).
(d) In the evening, the shadow points East (opposite to where the Sun sets in the West).
(a) Cardboard is opaque, so it blocks all light from passing through. Frosted glass is translucent, so it allows some light to pass through. Therefore, the shadow formed by cardboard is darker because no light reaches behind it, while the shadow formed by frosted glass is lighter because some light still passes through.
(b) Clear glass is transparent and allows most of the light to pass through it, so no shadow is formed on the screen.