Primary 6 PSLE Science Light Quiz

Primary 6 PSLE Science Quiz - Light: Answer Key

Total Marks: 40

Section A: Multiple Choice

Section A Total: 8 marks

Section B: Short Answer

9. Two properties of light: [2 marks]

• Light travels in straight lines (rectilinear propagation) [1]
• Light can be reflected [1] OR Light can be refracted / Light transfers energy / Light travels very fast

Teaching note: Understanding light's straight-line travel explains shadows and eclipses. Reflection allows us to see non-luminous objects.

10. (a) Reflection of light: [1 mark]

• When light bounces off a surface and changes direction

(b) Laws of reflection: [2 marks]

• The angle of incidence equals the angle of reflection [1]
• The incident ray, reflected ray, and normal all lie in the same plane [1]

Teaching note: "i = r" is the key equation. The normal is an imaginary line perpendicular to the surface at the point where light hits.

11. (a) Angle of incidence = 35° [1]

(b) Angle of reflection = 35° [1]

(c) The law of reflection states that the angle of incidence always equals the angle of reflection (or i = r) [1]

Teaching note: These angles are always measured from the normal, not from the mirror surface. Common mistake: measuring 55° (from mirror surface) instead of 35° (from normal).

12. (a) Explanation of why pool appears shallower: [2 marks]

• Light travels from the bottom of the pool through water and bends away from the normal as it exits into air (refraction) [1]
• Our eyes trace the light back in a straight line, making the bottom appear higher up (closer to the surface) than it really is [1]

(b) Another example: [1 mark]

• A drinking straw appears bent at the water's surface / A fish appears closer to the surface than it really is / A coin in a beaker becomes visible when water is added

13. (a) Point F is the focal point (or principal focus) [1]

(b) Focal length meaning: [2 marks]

• The distance from the center of the lens to the focal point [1]
• It is the distance where parallel rays of light are brought to a focus after passing through the lens [1]

(c) Use of convex lens: [1 mark]

• Magnifying glass / Eye glasses for long-sightedness / Camera lens / Telescope / Projector / Microscope

14. (a) Equipment: prism (or glass prism / triangular prism) [1]

(b) Seven colours in order (most bent first): [2 marks]

• Violet, indigo, blue, green, yellow, orange, red [2] (deduct [1] for each error in sequence, minimum 0)

Teaching note: Mnemonic: VIBGYOR backwards for most bent to least bent, or ROYGBIV forwards for least bent to most bent. Violet bends most because it has the shortest wavelength; red bends least with longest wavelength.

15. (a) Dispersion of light (or splitting of white light) [1]

(b) Red light is bent the least [1]

• Red light has the longest wavelength (or lowest frequency) among visible colours, so it is deviated least by the prism [1]

Teaching note: Different wavelengths refract by different amounts. Shorter wavelengths (violet/blue) interact more strongly with the glass, bending more.

16. (a) Ray diagram completion: [2 marks]

• Ray 1: From top of object, parallel to axis, then through focal point F on opposite side [1]
• Ray 2: From top of object, straight through center of lens without bending [1]
• Image forms where rays intersect (between F and 2F, inverted, diminished)

(b) Image characteristics: [3 marks]

• Diminished (smaller than object) [1]
• Inverted (upside down) [1]
• Real (can be projected on a screen / rays actually converge there) [1]

Teaching note: When object is beyond 2F (30 cm > 2 × 10 cm = 20 cm), image forms between F and 2F on opposite side. This is the standard camera arrangement.

Section C: Longer Answer

17. (a) Graph plotting: [2 marks]

• Correct axes labels with units [1]
• All points plotted accurately and smooth curve/line drawn [1]

(b) Pattern description: [2 marks]

• As angle of incidence increases, angle of refraction also increases [1]
• But angle of refraction increases more slowly than angle of incidence (or the increase is not proportional / curve levels off) [1]

(c) Estimated angle of refraction at 50° incidence: approximately 30°–32° [2]

• Reading from graph at 50° on horizontal axis, up to curve, across to vertical axis [1]
• Acceptable range 30°–32° based on curve trend [1]

18. (a) Eye defect: Short-sightedness (or myopia) [1]

(b) Explanation: [2 marks]

• The eyeball is too long, or the lens is too curved [1]
• Light from distant objects focuses in front of the retina instead of on it, so the image is blurry [1]

(c) Correcting lens: Concave lens (or diverging lens) [1]

• The concave lens diverges light rays before they enter the eye, so they spread out slightly [1]
• This means the eye's own lens can now focus the light onto the retina instead of in front of it [1]

Teaching note: Contrast with long-sightedness (hyperopia), where near objects blur because image would form behind retina; corrected with convex lens.

19. (a) Light path tracing: [2 marks]

• Light from object enters periscope, hits upper mirror at 45°, reflects downward [1]
• Hits lower mirror at 45°, reflects horizontally to eye; arrows show light traveling left→down→right [1]

(b) Why 45° placement: [2 marks]

• At 45°, the angle of incidence equals 45°, so angle of reflection equals 45° [1]
• This turns the light through exactly 90° (downward or sideways), allowing the periscope to "see" around corners while keeping the tube vertical [1]

Teaching note: Two reflections each turn light 90°, total 180° direction change, so observer sees object at same height but from concealed position.

20. (a) Variables: [2 marks]

• Manipulated variable: Colour of the can (or surface colour / paint colour) [1]
• Responding variable: Temperature of the water (or final temperature / temperature increase) [1]

(b) Why identical cans: [1 mark]

• To ensure fair test / so that only colour affects result, not size or shape; to control variables

(c) Explanation of results: [3 marks]

• Black can: Water reached highest temperature (38°C), so black absorbs the most light energy / black is the best absorber of light/heat energy [1]
• Silver can: Water stayed coolest (22°C), so silver absorbs the least light energy / silver is the poorest absorber (best reflector) [1]
• Dark/dull colours absorb more, light/shiny colours reflect more; black absorbs all colours, silver reflects all colours [1]

(d) Improvement for reliability: [1 mark]

• Repeat the experiment several times and calculate average temperatures / use more accurate thermometer / ensure same sunlight intensity for all cans / place cans same distance apart

Grand Total: 40 marks

Common Mistakes to Avoid:

• Confusing concave and convex lenses (concave = thinner middle, diverges; convex = thicker middle, converges)
• Forgetting that image distance in plane mirror equals object distance; total distance is double
• Measuring angles of incidence/reflection from the mirror surface instead of from the normal
• Confusing short-sightedness (myopia, corrected by concave lens) with long-sightedness (hyperopia, corrected by convex lens)