Primary 5 Science Heat Quiz

Primary 5 Science Quiz - Heat (Answer Key)

Total Marks: 40

Section A: Multiple-Choice Questions (10 marks)

1. Answer: B [1]
Explanation: Heat is a form of energy (measured in joules) that flows from hot to cold. Temperature is a measure of how hot or cold an object is (measured in °C). They are related but different concepts.

2. Answer: B [1]
Explanation: Metal is a good conductor of heat. 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 fast. Both spoons are at the same room temperature.

3. Answer: B [1]
Explanation: When a solid is heated, its particles gain kinetic energy and vibrate more vigorously about their fixed positions. This increased vibration pushes particles slightly further apart, causing the solid to expand.

4. Answer: C [1]
Explanation: Copper is a metal and an excellent conductor of heat. Air and water are poor conductors (fluids transfer heat mainly by convection). Plastic is an insulator (poor conductor).

5. Answer: B [1]
Explanation: Heat always flows from a region of higher temperature to a region of lower temperature. The warm water is at a higher temperature than the ice cube, so heat flows from the water to the ice.

6. Answer: C [1]
Explanation: Radiation transfers heat by electromagnetic waves (infrared) and does not need a medium. It can travel through a vacuum (e.g., heat from the Sun reaching Earth). Conduction and convection both require particles (a medium).

7. Answer: B [1]
Explanation: In fluids (liquids and gases), heat is transferred mainly by convection. Heated water at the bottom expands, becomes less dense, and rises. Cooler, denser water sinks to take its place, creating a convection current.

8. Answer: A [1]
Explanation: Heated water at the bottom becomes less dense and rises by convection, setting up a convection current that circulates heat throughout the water. If the element were at the top, only the top layer would be heated.

9. Answer: B [1]
Explanation: Both rulers are at the same freezer temperature. Metal conducts heat away from your warmer hand much faster than plastic, so your skin temperature drops more quickly, making the metal feel colder.

10. Answer: C [1]
Explanation: Dull black surfaces are the best absorbers (and emitters) of radiant heat. Shiny, light-coloured surfaces reflect most radiation and absorb very little.

Section B: Short Answer Questions (10 marks)

11. [2 marks — ½ mark per correct cell, total 6 cells × ½ = 3, but capped at 2 marks for the table; award 1 mark for 4–5 correct cells, 2 marks for all 6 correct]

Marking notes:

• Conduction: Needs medium (Yes); occurs mainly in solids (particles vibrate in place); example: spoon in hot soup / pan on stove.
• Convection: Needs medium (Yes); occurs in fluids (liquids & gases) where particles move; example: boiling water / hot air balloon / sea breeze.
• Radiation: Needs medium (No); occurs in vacuum and through transparent media; example: Sun’s heat / feeling warmth from a fire.

12.
(a) Answer: Point A is closest to the heat source, so heat reaches it first by conduction through the metal rod. [1]
Explanation: Heat travels through the solid metal rod by conduction from the hot end (left) to the cold end (right). The wax at A melts first because it receives heat earliest.

(b) Answer: Conduction [1]
Explanation: Heat transfer through a solid (metal rod) without movement of the material itself is conduction.

13.
(a) Answer: Styrofoam cup [1]
(b) Answer: Styrofoam is a poor conductor of heat (good insulator). It traps air in small pockets, reducing heat loss by conduction and convection, keeping the hot chocolate warm longer. [1]
Explanation: Metal and ceramic are good conductors — they would transfer heat quickly to the surroundings. Styrofoam’s structure minimises heat transfer.

14.
(a) Answer: The vacuum has no particles (or very few), so heat cannot be transferred by conduction or convection across the gap. [1]
Explanation: Both conduction and convection require a medium (particles). A vacuum eliminates these two heat loss paths.

(b) Answer: The shiny silvered surfaces reflect radiant heat back into the flask (and reflect external radiation away), reducing heat loss by radiation. [1]
Explanation: Radiation does not need a medium. Silvered surfaces are poor absorbers/emitters and good reflectors of infrared radiation.

15.
(a) Answer: Radiation [1]
Explanation: Heat from the Sun travels through the vacuum of space and the atmosphere by radiation (infrared waves).

(b) Answer: Black surfaces are better absorbers of radiant heat than white surfaces. The black seats absorb more of the Sun’s radiation and convert it to heat, making them hotter. [1]
Explanation: Dull black surfaces absorb most incident radiation; shiny white surfaces reflect most.

Section C: Structured / Open-Ended Questions (20 marks)

16.
(a) Answer: Copper. The drawing pin on the copper rod dropped in the shortest time (15 s), showing heat travelled through it the fastest. [1]
Explanation: Shorter time = faster heat conduction = better conductor.

(b) Answer: To ensure a fair test — only the material (type of rod) is changed (independent variable), while length and diameter (which affect conduction rate) are kept constant (controlled variables). [1]
Explanation: Thicker/longer rods conduct heat differently. Controlling these ensures any difference in time is due only to the material.

(c) Answer: Glass is a very poor conductor of heat (an insulator). Heat hardly travels through it, so the wax did not melt even after 300 s. [1]
Explanation: Glass lacks free electrons and has a rigid structure that hinders heat transfer by conduction.

(d) Answer (any one):

• Use the same amount/volume of wax for each drawing pin.
• Ensure the hot water temperature is constant and the same for all rods.
• Start timing for all rods simultaneously.
• Use rods of the same mass (not just length/diameter). [1]
  Explanation: Any variable that could affect how quickly heat reaches the wax must be controlled.

17.
(a) Answer: When air is heated, its particles gain energy, move faster, and spread further apart. The air expands, becomes less dense than the surrounding cooler air, and rises due to buoyancy (upthrust). [2]
Mark breakdown: 1 mark for "air expands / particles spread out / less dense"; 1 mark for "rises because it is less dense than surrounding cool air / buoyancy".

(b) Answer: Convection [1]
Explanation: The movement of heated fluid (air) rising and cooler fluid sinking is a convection current.

(c) Answer: The air inside cools down, becomes denser, and the balloon descends / sinks. [1]
Explanation: Without continuous heating, heat escapes by conduction/convection/radiation. Cool air is denser, so the balloon loses buoyancy.

18.
(a) Answer: The dull black can. [1]
(b) Answer: Dull black surfaces are better absorbers of radiant heat than shiny white surfaces. The black can absorbs more heat from the lamp, transferring it to the water. [1]
Explanation: Colour and texture affect radiation absorption. Black + dull = best absorber; white + shiny = worst absorber (best reflector).

(c) Answer (any two, 1 mark each):

• Same volume of water (100 mL) in each can.
• Same initial water temperature (28°C).
• Same distance from the heat lamp.
• Same heat lamp intensity / power.
• Same duration of heating (10 minutes).
• Same can size, shape, and material (only colour differs).
• Same surrounding conditions (room temperature, air flow). [2]
  Explanation: Fair test requires only the independent variable (colour) to change; all others controlled.

19.
(a) Answer: Black surfaces are the best absorbers of radiant heat from the Sun. [1]
Explanation: Maximises absorption of solar radiation to heat the water.

(b) Answer: Copper is a good conductor of heat; it transfers heat from the absorber plate to the water quickly. Plastic is a poor conductor (insulator) and would not transfer heat efficiently. [1]
Explanation: The pipes must conduct heat from the hot plate to the water inside. Copper’s high thermal conductivity makes it ideal.

(c) Answer: The Sun’s radiation heats the black absorber plate. The plate conducts heat to the copper pipes. Water in the pipes absorbs heat, expands, becomes less dense, and rises (convection). Cold water from the bottom inlet sinks to replace it, creating a continuous convection current (thermosiphon) without a pump. [2]
Mark breakdown: 1 mark for "radiation heats plate → conduction to pipes → water heated"; 1 mark for "hot water rises (less dense), cold water sinks, convection cycle / thermosiphon".

20.
(a) Answer: The metal spoon handle. [1]
(b) Answer: Metal is a good conductor of heat. Heat from the hot soup conducts quickly along the metal spoon to the handle. Plastic is a poor conductor (insulator), so heat hardly reaches the plastic handle. [1]
Explanation: Conduction rate depends on material. Metals have free electrons that transfer energy rapidly.

(c) Answer (any two, 1 mark each):

• Convection (warm soup rises, cool air sinks above it).
• Radiation (hot soup emits infrared radiation to surroundings).
• Conduction (heat conducts through the bowl to the table/air).
• Evaporation (water molecules escape, taking latent heat). [2]
  Explanation: A hot liquid in an open bowl loses heat by all these processes. Evaporation is often the largest contributor.

End of Answer Key