Primary 6 PSLE Science Heat Quiz

Primary 6 PSLE Science Quiz - Heat (Answer Key)

Total Marks: 50

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

1. Answer: B
Explanation: Heat is a form of energy (measured in joules) that flows due to a temperature difference. Temperature is a measure of the degree of hotness or coldness of a body (measured in °C or K). They are related but distinct concepts. Heat flows from hotter to colder objects, not the reverse.

2. Answer: B
Explanation: Metal is a good conductor of heat. When you touch a metal spoon, it conducts heat away from your hand quickly, making it feel colder. Wood is a poor conductor (insulator), so it does not draw heat from your hand as quickly. Both spoons are at the same room temperature.

3. Answer: B
Explanation: When a substance is heated, its particles gain kinetic energy and vibrate/move faster. The increased motion causes particles to push further apart, leading to expansion (increase in volume). This applies to solids, liquids, and gases.

4. Answer: C
Explanation: Copper is a metal and an excellent conductor of heat. Air and plastic are insulators (poor conductors). Water conducts heat better than air but much worse than metals like copper.

5. Answer: B
Explanation: Heat always flows from a region of higher temperature to a region of lower temperature. The water at room temperature (~25–30°C) is warmer than the ice cube (0°C), so heat flows from the water to the ice cube, causing the ice to melt.

6. Answer: C
Explanation: Radiation is the transfer of heat by electromagnetic waves (infrared radiation). It does not require a medium and can travel through a vacuum (e.g., heat from the Sun reaching Earth). Conduction and convection both require a medium (particles).

7. Answer: B
Explanation: Convection is heat transfer in fluids (liquids and gases) due to the movement of the fluid itself. When water at the bottom is heated, it expands, becomes less dense, and rises. Cooler, denser water sinks to take its place, creating a convection current.

8. Answer: B
Explanation: Placing the heating element at the bottom allows convection currents to form: heated water rises, cooler water sinks, and the entire volume of water heats evenly. If the element were at the top, only the top layer would heat up (hot water stays at the top).

9. Answer: B
Explanation: Shiny, light-coloured (silver) surfaces are poor absorbers and poor emitters of heat radiation. They reflect most of the radiation that falls on them. Dull, dark surfaces are good absorbers and good emitters.

10. Answer: A
Explanation: Solar water heaters use black (dull, dark) panels because dark surfaces absorb heat radiation from the Sun very effectively. Vacuum flasks use shiny surfaces to reduce radiation absorption/emission. Shiny exteriors on pots reflect heat away. White refrigerator exteriors reflect heat.

Section B: Structured Questions (8 × 2 marks = 16 marks)

11.
(a) Conduction [1]
(b) Heat travels through the metal rod by conduction from the hot end (near A) to the cooler end (near D). Point A is closest to the heat source, so it receives heat first and its temperature rises fastest, melting the wax there first. Heat takes time to conduct along the rod to reach point D. [1]
Marking note: Must mention heat travels from hot to cold, A is nearer the source, and conduction takes time.

12.
(a) Beaker Y (wrapped in black paper) [1]
(b) Black, dull surfaces are good absorbers of heat radiation. The black paper on Beaker Y absorbs more heat radiation from the lamp than the shiny aluminium foil on Beaker X, which reflects most of the radiation. Therefore, more heat is transferred to the water in Beaker Y. [1]
Marking note: Must link black/dull surface to good absorption, shiny surface to reflection/poor absorption.

13.
(a) Conduction and convection [1]
(b) The shiny inner walls are poor emitters of heat radiation. They reflect heat radiation from the hot soup back into the flask, reducing heat loss by radiation. [1]
Marking note: Vacuum stops conduction and convection (need particles). Shiny surfaces reduce radiation.

14.
(a) Copper > Aluminium > Glass (highest to lowest temperature at far end) [1]
(b) Glass is a poor conductor of heat (insulator). Its particles are not free to vibrate and transfer energy as effectively as in metals. Copper and aluminium are metals with free electrons that transfer heat quickly by conduction. [1]
Marking note: Must identify glass as poor conductor/insulator and contrast with metals.

15.
(a) When air is heated, its particles gain energy, move faster, and spread further apart. The air expands, becomes less dense, and rises. Cool air is denser and sinks. [1]
(b) No, convection would not heat the room effectively. Warm air from a ceiling radiator would stay at the top (ceiling) because it is less dense. It would not sink to heat the lower part of the room where people are. Cool air at the floor would not be drawn up to the radiator to create a convection current. [1]
Marking note: Must explain density difference and why ceiling placement breaks the convection cycle.

16.
(a) When the metal ball is heated, its particles gain kinetic energy and vibrate more vigorously about their fixed positions. The increased vibration causes the average distance between particles to increase, so the ball expands (its volume increases). [1]
(b) Examples: Gaps left between railway tracks / expansion joints in bridges / metal lids on glass jars loosened by hot water / bimetallic strips in thermostats / overhead power lines sagging in heat. (Any one valid example) [1]
Marking note: Particle explanation must mention increased vibration and increased spacing.

17.
(a) The can painted dull black [1]
(b) Dull black surfaces are good emitters of heat radiation. The dull black can radiates heat energy to the surroundings faster than the shiny white can, which is a poor emitter. Therefore, the water in the dull black can loses heat more quickly and cools faster. [1]
Marking note: Must link dull black to good emitter, shiny white to poor emitter.

18.
(a) Black, dull surfaces are good absorbers of heat radiation. The black pot absorbs most of the sunlight (radiant energy) focused on it, converting it to heat energy, so it heats up faster. [1]
(b) The shiny parabolic reflector reflects and focuses parallel rays of sunlight onto the cooking pot at the focal point. Its shiny surface ensures minimal absorption and maximum reflection of the sunlight. [1]
Marking note: Pot = absorber (black). Reflector = focuses radiation (shiny).

Section C: Open-Ended Questions (4 × 6 marks = 24 marks)

19.
(a) Dull black can. Temperature rise = 42°C – 25°C = 17°C. [2]
Mark breakdown: 1 mark for identifying dull black can, 1 mark for correct calculation (17°C).

(b) 1. Colour of surface: Dull black absorbs more heat than dull white (compare 42°C vs 35°C).
2. Shine/texture of surface: Dull surfaces absorb more heat than shiny surfaces of the same colour (compare dull black 42°C vs shiny black 38°C; dull white 35°C vs shiny silver 30°C). [2]
Mark breakdown: 1 mark for colour factor with evidence, 1 mark for shine/texture factor with evidence.

(c) No, the conclusion is not fully supported. The results show that a dull black surface (42°C) absorbs more heat than a dull white surface (35°C), but a shiny black surface (38°C) absorbs less heat than a dull white surface (35°C is incorrect; 38°C > 35°C). Wait: shiny black (38°C) > dull white (35°C). So black surfaces are not always better than white surfaces if shine differs. The conclusion ignores the effect of surface texture (shiny vs dull). A dull white surface absorbs less than a shiny black surface in this experiment. [2]
Mark breakdown: 1 mark for "No/not fully supported", 1 mark for correct explanation using data (shiny black 38°C > dull white 35°C shows texture matters).

20.
(a) Air (or argon) is a gas and a poor conductor of heat. The narrow gap between the panes traps the gas, preventing large-scale convection currents from forming (the gap is too narrow for effective convection). This reduces heat transfer by both conduction (gas is poor conductor) and convection (currents restricted). [2]
Mark breakdown: 1 mark for poor conduction explanation, 1 mark for restricted convection explanation.

(b) The low-E coating reflects long-wave infrared radiation (heat radiation) from the warm room back into the room, instead of allowing it to pass through the glass to the outside. This reduces heat loss by radiation. [2]
Mark breakdown: 1 mark for reflecting heat radiation back inside, 1 mark for reducing radiative heat loss.

(c) Argon gas has a lower thermal conductivity than air (it is a poorer conductor of heat). With argon in the gap, heat transfer by conduction across the gap is reduced further compared to air. Since convection is already minimal in the narrow gap, the main improvement is reduced conductive heat loss, improving overall insulation (lower U-value). [2]
Mark breakdown: 1 mark for argon being poorer conductor than air, 1 mark for reduced conduction improving insulation.

End of Answer Key