Primary 5 Science Light Quiz

Primary 5 Science Quiz - Light (Answer Key)

Total Marks: 40

Section A: Multiple-Choice Questions (10 × 1 mark = 10 marks)

1. C – The Sun is a natural source of light. Torch, candle flame, and light bulb are artificial sources.
Mark: 1

2. B – Light travels in straight lines. This is a fundamental property of light.
Mark: 1

3. C – Clear glass window allows light to pass through completely so objects can be seen clearly through it. Wooden door and cardboard box are opaque; frosted glass is translucent.
Mark: 1

4. C – Reflection occurs when light bounces off a smooth, shiny surface like a mirror.
Mark: 1

5. B – A shadow is formed when an opaque or translucent object blocks light from reaching a surface.
Mark: 1

6. D – A small (point) light source far from the object produces the sharpest shadow because the light rays are nearly parallel. Large or close sources produce fuzzy shadows (umbra and penumbra).
Mark: 1

7. B – Law of reflection: Angle of incidence = Angle of reflection. If angle of incidence is 30°, angle of reflection is also 30°.
Mark: 1

8. A – Light can travel through a vacuum (e.g., sunlight reaching Earth). Light travels slower in water than in air; it travels through transparent objects; it travels in straight lines.
Mark: 1

9. C – This is refraction: light changes direction when it passes from one medium (air) into another (water) of different optical density.
Mark: 1

10. A – Object A is closest to the light source. The closer an object is to the light source, the larger the shadow cast on a fixed screen (due to greater divergence of light rays).
Mark: 1

Section B: Short Answer Questions (5 × 2 marks = 10 marks)

11. (2 marks – ½ mark each correct classification)

Marking notes:

• Luminous objects emit their own light.
• Moon and mirror only reflect light; they do not produce their own.
• Common mistake: Classifying Moon as luminous.

12. (2 marks)
(a) Refraction – The bending of light when it passes from one medium to another of different optical density.
Mark: 1

(b) Towards the normal – Light slows down when entering a denser medium (glass), causing it to bend towards the normal.
Mark: 1

13. (2 marks)
The white light from the torch contains all colours. The red apple absorbs most colours (orange, yellow, green, blue, indigo, violet) and reflects red light into our eyes.
Mark breakdown:

• Mention white light contains all colours / apple absorbs other colours: 1 mark
• Apple reflects red light to our eyes: 1 mark

Teaching note: Emphasise that colour of an object is the colour of light it reflects.

14. (2 marks)
(a) Light travels in straight lines. (Accept: Light cannot bend around the object / Light is blocked by opaque objects.)
Mark: 1

(b) The shadow will become larger. When the object moves closer to the light source, the light rays diverge more, casting a larger shadow on the fixed screen.
Mark: 1

15. (2 marks – ½ mark each)

Marking notes:

• Transparent: allows light to pass through, objects seen clearly.
• Translucent: allows some light to pass, objects not seen clearly.
• Opaque: does not allow light to pass through.

Section C: Structured / Open-Ended Questions (5 × 4 marks = 20 marks)

16. (4 marks)
(a) Diagram: Light ray from object → strikes top mirror at 45° → reflects down tube (90° turn) → strikes bottom mirror at 45° → reflects horizontally to observer's eye. Arrows must show direction.
Mark: 1 (for correct path with arrows)

(b) 45° to the horizontal (or 45° to the vertical).
Mark: 1

(c) Plane mirrors produce upright, same-size, laterally inverted images without distortion. Curved mirrors would magnify, reduce, or distort the image, making it unsuitable for viewing objects at their true size and orientation.
Mark: 1

(d) The observer will not see the object / the image will be displaced / the light ray will not reach the observer's eye. The mirror must be at exactly 45° to turn the light ray by 90° down the tube.
Mark: 1

17. (4 marks)
(a) As the distance between the light source and the object increases, the height of the shadow decreases. (Inverse relationship)
Mark: 1

(b) Approximately 13–14 cm (accept 12–15 cm with valid reasoning). The shadow height decreases at a decreasing rate; extrapolating from the trend (40→25→20→17→15), the next drop is about 2–3 cm.
Mark: 1

(c) When the light source is further away, the light rays reaching the object are more parallel (less divergent). This causes the shadow to be smaller and sharper, closer to the actual size of the object.
Mark: 1

(d) Distance between object and screen (or: size of object, size of light source, brightness of light source, position of screen).
Mark: 1

18. (4 marks)
(a) Dispersion (or: Dispersion of light).
Mark: 1

(b) Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV).
Mark: 1 (all 7 in correct order)

(c) Different colours of light travel at different speeds in glass (different refractive indices). Violet light slows down the most and bends the most (shortest wavelength); red light slows down the least and bends the least (longest wavelength). This causes the colours to separate.
Mark: 1

(d) Only a red band/line will be seen on the screen. The red filter only allows red light to pass through; all other colours are absorbed. Since only red light enters the prism, no dispersion occurs.
Mark: 1

19. (4 marks)
(a) Diagram: Similar to periscope in Q16. Cardboard tube with two plane mirrors at 45° at each end. Light from object above fence → top mirror (45°) → reflects down tube → bottom mirror (45°) → reflects to eye. Labels: Top mirror, Bottom mirror, Cardboard tube, Object, Eye, Light ray path with arrows.
Mark: 1 (correct arrangement with labels)

(b) Angle of incidence = Angle of reflection (Law of reflection).
Mark: 1

(c) The image would appear magnified / larger / distorted. A concave mirror converges light rays, producing a magnified virtual image when the object is within the focal length.
Mark: 1

(d) Use a longer tube / ensure mirrors are perfectly flat and at exactly 45° / use higher quality mirrors with less absorption / paint inside of tube black to reduce internal reflections. (Any one valid improvement)
Mark: 1

20. (4 marks)
(a) The angle of incidence must be greater than the critical angle, and light must travel from a denser medium (core) to a less dense medium (cladding).
Mark: 1 (both conditions needed)

(b) Optical fibres can transmit data over longer distances with less signal loss / higher bandwidth / immune to electromagnetic interference / lighter and thinner. (Any one valid advantage)
Mark: 1

(c) For total internal reflection to occur, light must travel from a medium of higher refractive index (core) to a medium of lower refractive index (cladding). If the cladding had a higher or equal refractive index, light would refract into the cladding instead of reflecting back into the core.
Mark: 1

(d) Light travels in straight lines / Light can be reflected (total internal reflection) / Light can travel through transparent fibres. (Any one relevant property – most directly: Light can undergo total internal reflection to travel along curved paths.)
Mark: 1

Total: 40 marks

Common Mistakes to Watch For:

1. Q3, Q15: Confusing translucent and transparent. Transparent = see clearly; Translucent = see blurred/shadow only.
2. Q6, Q10, Q14, Q17: Shadow size relationships. Closer to light source = larger shadow. Further from light source = smaller shadow.
3. Q7, Q16: Law of reflection. Angle measured from normal, not from mirror surface.
4. Q9, Q12, Q18: Refraction vs Reflection. Refraction = bending when changing medium. Reflection = bouncing off surface.
5. Q13: Colour of object = colour reflected, not colour absorbed.
6. Q18: Order of spectrum (ROYGBIV) and which colour deviates most (violet) vs least (red).
7. Q20: Total internal reflection requires: (1) denser to less dense medium, (2) angle > critical angle.