Primary 4 Science Light Quiz

Primary 4 Science Quiz - Light — Answer Key

Total Marks: 40

Section A: Multiple Choice Questions (10 marks)

1. (C) straight

• Light travels in a straight line. This is a fundamental property of light. [1]

2. (C) The Sun

• The Sun produces its own light and is a natural source. The Moon only reflects light and does not produce its own. [1]

3. (B) blocked

• A shadow is formed when an object blocks the path of light. [1]

4. (B) directly above

• When the light source is directly overhead, the shadow is shortest because light hits the top of the object and falls directly below it. [1]

5. (C) Clear glass

• Clear glass is transparent and allows most light to pass through. Wood, metal, and cardboard are opaque. [1]

6. (C) bounces back (reflects)

• When light hits a smooth, shiny surface, it reflects (bounces back). This is the law of reflection. [1]

7. (C) black

• A shadow is the area where light is blocked, so no light reaches that area. It appears black. [1]

8. (C) A wooden door

• An opaque object does not allow light to pass through. Wooden doors block all light. [1]

9. (B) bigger

• When the object is closer to the light source, it blocks a wider spread of light rays, producing a larger shadow. [1]

10. (B) bounces

• We see objects because light bounces (reflects) off their surfaces and enters our eyes. [1]

Section B: Short Answer Questions (20 marks)

11. Light travels in a straight line. [1]

• Accept any one valid characteristic: "Light travels in a straight line" / "Light does not need a medium to travel" / "Light can be blocked by opaque objects."

12. (a) A dark shadow (of the ball) would appear on the screen. [1]

• The ball blocks the light from the torch, so a shadow forms on the screen.

(b) The ball is an opaque object. [1] It blocks the light from the torch, preventing light from reaching the screen behind it. [1] The area where light cannot reach appears as a dark shadow.

• Marking: 1 mark for identifying the ball as opaque; 1 mark for explaining that light is blocked.

13. [3 — 1 mark each]

• Transparent = allows most/all light through. Translucent = allows some light through. Opaque = allows no light through.

14. (a) At 12 noon. [1]

• The Sun is highest in the sky at noon, so shadows are shortest.

(b) The position of the Sun changes throughout the day. [1] In the morning (9 a.m.), the Sun is lower in the sky, so the shadow is longer. At noon, the Sun is higher (closer to directly overhead), so the shadow is shorter. [1]

• Marking: 1 mark for stating the Sun's position changes; 1 mark for linking Sun height to shadow length.

15. A brick wall is an opaque material. [1] It does not allow light to pass through it, so light cannot travel through the wall to reach our eyes from the other side. [1]

• Marking: 1 mark for identifying brick wall as opaque; 1 mark for explaining that light cannot pass through.

16. [2 — 1 mark each]

• Difference 1: A transparent object forms a very faint or no shadow because most light passes through it, while an opaque object forms a dark shadow because it blocks all light.
• Difference 2: The shadow of a transparent object is light/grey, while the shadow of an opaque object is dark/black.
• Accept any two valid differences related to shadow darkness, light transmission, or shadow visibility.

17. [2]

• Darkest: Book (opaque — blocks all light)
• Middle: Frosted glass pane (translucent — blocks some light)
• Lightest: Clear plastic sheet (transparent — allows most light through)
• Award 2 marks for all three correct. Award 1 mark if two are in the correct position.

18. [1]

• Accept any one valid example:
  • Mirrors use reflection so we can see ourselves.
  • Reflective strips on clothing help cyclists be seen at night.
  • Periscopes use reflection to see around corners.
  • Rear-view mirrors in cars use reflection.

Section C: Structured / Application Questions (10 marks)

19. (a) [3]

• Expected diagram: Straight lines drawn from the light source to the edges of the object, continuing to the screen. The area on the screen between the two extended lines (where light does not reach) should be shaded to represent the shadow.
• Marking:
  • 1 mark for showing light rays as straight lines from the source.
  • 1 mark for showing light being blocked by the object.
  • 1 mark for correctly shading/indicating the shadow region on the screen.

(b) The shadow becomes smaller. [1] When the object is moved closer to the screen, the object blocks a narrower spread of light rays, so the shadow on the screen is smaller. [1]

• Marking: 1 mark for correct prediction (smaller); 1 mark for correct explanation linking object position to shadow size.

20. (a) The shadow formed by the wooden block is dark (black) and sharp/clear. [2]

• The wooden block is opaque, so it blocks all the light from the torch. No light reaches the screen behind it, resulting in a dark, well-defined shadow.
• Marking: 1 mark for "dark/black"; 1 mark for "sharp/clear/well-defined" (or equivalent).

(b) The shadow formed by the tracing paper would be lighter (grey/faint) compared to the wooden block's dark shadow. [1] Tracing paper is a translucent material. [1] It allows some light to pass through it, so some light still reaches the screen behind it. This means the shadow is not completely dark — it appears grey or faint. [1]

• Marking: 1 mark for describing the shadow as lighter/grey; 1 mark for identifying tracing paper as translucent; 1 mark for explaining that some light passes through.

End of Answer Key