Primary 6 PSLE Science Light Quiz

Primary 6 PSLE Science Quiz - Light (Answer Key)

Total Marks: 40

Section A: Multiple-Choice Questions (10 marks)

1. C — The Sun is a natural source of light. Candle flame, torchlight, and light bulbs are artificial sources. [1]

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

3. B — Clear glass window is transparent (allows most light to pass through). Wooden door and cardboard box are opaque; metal sheet is opaque. [1]

4. C — When light hits a smooth, shiny surface like a mirror, it is reflected. Reflection follows the law of reflection. [1]

5. B — A shadow is formed when an opaque object blocks light. Light travels in straight lines, so the blocked region behind the object receives no light, forming a shadow. [1]

6. B — According to the law of reflection, the angle of incidence equals the angle of reflection. Given angle of incidence = 30°, angle of reflection = 30°. [1]

7. D — A shadow is formed on the side of the object opposite the light source because light travels in straight lines and is blocked by the opaque object. [1]

8. C — White light is made up of seven colours (red, orange, yellow, green, blue, indigo, violet), as seen in a rainbow or spectrum. [1]

9. C — The splitting of white light into its component colours is called dispersion. Refraction is the bending of light; dispersion is the separation of colours due to different wavelengths refracting by different amounts. [1]

10. D — When the object is moved closer to the light source, the shadow becomes larger (more light rays are blocked at wider angles) and blurrier (the penumbra region increases because the light source is not a perfect point source). [1]

Section B: Structured Questions (12 marks)

11. [2 marks total, 0.5 marks each]

Marking notes:

• Transparent: allows light to pass through clearly (clear plastic ruler).
• Translucent: allows some light to pass through but scatters it (frosted glass, tissue paper).
• Opaque: does not allow light to pass through (aluminium foil).

12. (a) Refraction — The bending of light when it passes from one medium to another of different optical density. [1]

(b) The speed of light decreases when it enters the glass block. Glass is optically denser than air, so light slows down. [1]

Marking notes:

• Accept "light slows down" or "speed decreases".
• Do not accept "light stops" or "speed increases".

13. (a) The apple appears red because it reflects red light and absorbs all other colours of white light. The reflected red light enters our eyes. [1]

(b) The apple will appear black (or dark). A red apple absorbs blue light (since it only reflects red). When blue light shines on it, there is no red light to reflect, so no light reaches the eye, making it appear black. [1]

Marking notes:

• For (a), must mention both reflection of red and absorption of other colours.
• For (b), "black" or "dark" accepted. Explanation must link to absorption of blue light.

14. (a) Refraction — The bending of light as it passes from water (denser medium) to air (less dense medium). [1]

(b) Diagram should show: Two rays from the submerged end of the stick, travelling upwards, bending away from the normal at the water surface, and entering the eye. The eye perceives the rays as coming from a higher position (apparent position), making the stick look bent. [1]

Marking notes:

• Rays must bend away from normal at water-air boundary.
• Arrows must show direction from object to eye.
• Virtual image position (apparent position) should be indicated.

15. (a) The Moon blocks light from the Sun during a solar eclipse. [1]

(b) Total solar eclipse in the umbra; partial solar eclipse in the penumbra. [1]

Marking notes:

• Umbra = total shadow (complete blockage) → total eclipse.
• Penumbra = partial shadow (partial blockage) → partial eclipse.

16. (a) As the distance between the light source and the object increases, the size of the shadow decreases. (Inverse relationship) [1]

(b) Approximately 10 cm (accept 9–11 cm). The pattern shows decreasing increments: 30→20 (–10), 20→15 (–5), 15→12 (–3). The next decrease is approximately 2 cm, giving ~10 cm. [1]

Marking notes:

• For (a), accept "the further the light source, the smaller the shadow".
• For (b), accept reasonable extrapolation based on trend. The relationship is not perfectly linear due to geometry (similar triangles), but the trend is clear.

Section C: Open-Ended Questions (18 marks)

17. (a) Diagram should show: Light ray from object → strikes top mirror at 45° → reflects down tube → strikes bottom mirror at 45° → reflects horizontally to eye. Arrows showing direction from object to eye. [2]

Marking breakdown:

• Correct path via both mirrors: 1 mark
• Correct angles (45° incidence/reflection at both mirrors): 1 mark
• Arrows showing correct direction: included in path mark

(b) 45° — The mirror is fixed at 45° to the vertical/horizontal, so the angle of incidence is 45°. [1]

(c) Plane mirrors produce upright, same-sized, laterally inverted images without distortion. Curved mirrors would distort the image (magnify or reduce it), making it difficult to view objects accurately. [1]

Marking notes:

• Key point: plane mirrors give true-to-size, undistorted view.
• Accept "plane mirrors do not magnify or reduce the image".

(d) The observer will not see the object (or will see a different view / the image will be shifted out of view). The light ray will not be directed into the eye because the angle of reflection changes. [1]

(e) Submarines use periscopes to see above water while submerged. (Also accept: tanks, trenches, looking over walls/crowds.) [1]

18. (a) Dispersion (or "dispersion of white light"). [1]

(b) Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV) — Red is least deviated, violet is most deviated. [1]

(c) White light consists of seven colours, each with a different wavelength. When white light enters the prism, each colour refracts (bends) by a different amount because the refractive index of glass is different for different wavelengths. Shorter wavelengths (violet) bend more; longer wavelengths (red) bend less. This separates the colours into a spectrum. [2]

Marking breakdown:

• White light contains different colours/wavelengths: 1 mark
• Different colours bend by different amounts (different refractive indices): 1 mark
• Mention violet bends most, red bends least: included in explanation

(d) No, a spectrum will not be observed. A rectangular glass block has parallel sides. Light refracts upon entry but refracts back by the same amount upon exit (emergent ray is parallel to incident ray). The colours recombine to form white light again. [1]

Marking notes:

• Key: parallel sides cause recombination.
• Accept "light enters and exits parallel, so colours recombine".

(e) Rainbow — formed when sunlight is dispersed by water droplets in the atmosphere. [1]

19. (a) The screen must be translucent (allows light to pass through so shadows can be seen from the other side) and smooth/flat (to produce clear, sharp shadows). [2]

Marking breakdown:

• Translucent: 1 mark
• Smooth/flat/white (for clear projection): 1 mark

(b) Opaque material blocks all light, creating a dark, well-defined shadow on the screen. If the puppets were transparent or translucent, light would pass through and no clear shadow would form. [1]

(c) The shadows will become larger. When the puppets are moved closer to the light source, they block light at wider angles (more divergent rays), casting a larger shadow on the fixed screen. This is due to similar triangles geometry: shadow size ∝ (distance from source to screen) / (distance from source to object). [2]

Marking breakdown:

• Shadows become larger: 1 mark
• Correct explanation (wider angle blocking / similar triangles / geometry): 1 mark

(d) The edges of the shadows will become blurrier (less sharp / more fuzzy). A larger light source acts like many point sources, each creating a slightly shifted shadow. These overlap to form a wider penumbra (partial shadow) at the edges. [1]

Marking notes:

• Key concept: larger source → larger penumbra → blurrier edges.
• Accept "shadows become less sharp" or "fuzzy edges".

20. (a) Red colour is observed. A red filter transmits (allows to pass) only red light and absorbs all other colours of white light. Only red light reaches the screen. [2]

Marking breakdown:

• Red observed: 1 mark
• Explanation (filter transmits red, absorbs other colours): 1 mark

(b) Black (or dark / no light). The red filter transmits only red light. The green filter transmits only green light. Since the red filter absorbs green light and the green filter absorbs red light, no light passes through both filters. The screen appears black. [2]

Marking breakdown:

• Black/dark: 1 mark
• Explanation (red filter blocks green, green filter blocks red, no common colour transmitted): 1 mark

(c) The blue object will appear black (or dark). A blue object appears blue because it reflects blue light and absorbs other colours (including red). When only red light shines on it, the red light is absorbed. No light is reflected to the eye, so it appears black. [2]

Marking breakdown:

• Black/dark: 1 mark
• Explanation (blue object absorbs red light, reflects only blue; no blue light in red LED): 1 mark

End of Answer Key