Primary 5 Science Heat Quiz

Primary 5 Science Quiz - Heat (Answer Key)

Total Marks: 40

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

1. Answer: C
Explanation: Heat is a form of energy, not matter. It transfers from hotter to colder regions (not colder to hotter). Heat can travel through a vacuum by radiation (e.g., Sun's heat reaching Earth).

2. Answer: B
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 are at room temperature.

3. Answer: B
Explanation: When heated, the metal ball expands (thermal expansion). Its diameter increases, becoming larger than the ring's inner diameter, so it cannot pass through. Mass and density do not increase with heating (mass stays same, density decreases as volume increases).

4. Answer: C
Explanation: Copper is a metal and an excellent conductor of heat. Plastic, wood, and air are poor conductors (insulators).

5. Answer: B
Explanation: The metal rod conducts heat from the hot water to your hand faster than the plastic rod. Both rods absorb heat, but the rate of conduction differs. This demonstrates that metal is a better conductor than plastic.

6. Answer: C
Explanation: The constriction (narrow section) in a clinical thermometer prevents the mercury from flowing back into the bulb immediately after removal from the mouth. This allows the temperature reading to be taken after the thermometer is removed. The mercury must be shaken down to reset.

7. Answer: C
Explanation: Heat from the Sun travels through the vacuum of space by radiation. Conduction and convection require a medium (particles), but space is a vacuum.

8. Answer: B
Explanation: Convection is heat transfer in fluids (liquids and gases) through the movement of the fluid itself. Hot water rises (less dense), cold water sinks (more dense), creating a convection current.

9. Answer: C
Explanation: Heat from a campfire warming your face is primarily by radiation (infrared waves). Sea breeze, land breeze, and hot air balloons involve convection (movement of air due to temperature differences).

10. Answer: B
Explanation: Cotton wool is a good insulator (poor conductor) because it traps air. It reduces heat loss by conduction and convection. Aluminium foil, copper, and steel are metals and good conductors, so they would allow heat to escape quickly.

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

11.
(a) Answer: The bimetallic strip bends because the two metals (brass and iron) expand at different rates when heated. Brass expands more than iron, so the brass side becomes longer, causing the strip to bend towards the iron side.
Marks: 1 mark for "different expansion rates" or "brass expands more than iron", 1 mark for "bends towards the metal that expands less (iron)".

(b) Answer: Brass expands more than iron when heated.
Marks: 1 mark

12.
(a) Answer: Gaps are left to allow for expansion of the metal rails on hot days. Without gaps, the rails would expand and buckle or bend, which could cause train derailment.
Marks: 1 mark for "allow expansion", 1 mark for "prevent buckling/bending/derailment".

(b) Answer: The rails would expand and buckle (bend sideways) or push against each other, potentially causing damage to the track and danger to trains.
Marks: 1 mark for "buckle/bend", 1 mark for "damage/danger" (or combined 2 marks for complete answer).

13.
(a) Answer: The vacuum prevents heat loss by conduction and convection because there are no particles (or very few) in a vacuum to transfer heat through these methods.
Marks: 1 mark for "no particles", 1 mark for "stops conduction and convection".

(b) Answer: The silvered (shiny) surfaces reflect radiant heat back into the flask (or reflect external heat away), reducing heat loss by radiation.
Marks: 1 mark for "reflect heat/radiation", 1 mark for "reduces radiation heat loss".

14.
(a) Answer: The type of metal rod (copper, aluminium, iron, brass).
Marks: 1 mark

(b) Answer: The time taken for the wax to melt and the drawing pin to drop (or the distance the heat travels along the rod in a fixed time).
Marks: 1 mark

15.
(a) Answer: 0°C
Marks: 1 mark

(b) Answer: 100°C
Marks: 1 mark

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

16.
(a) Answer: Copper is a good conductor of heat. It allows heat from the flame to transfer quickly and evenly to the food in the saucepan.
Marks: 1 mark for "good conductor", 1 mark for "quick/even heat transfer to food".

(b) Answer: Plastic is a poor conductor of heat (insulator). It prevents heat from the saucepan body from reaching the handle, so the handle stays cool and safe to hold.
Marks: 1 mark for "poor conductor/insulator", 1 mark for "handle stays cool/safe to hold".

(c) Answer: Heat continues to transfer from the hotter copper base to the cooler food until both reach the same temperature (thermal equilibrium). At this point, there is no net heat transfer between them.
Marks: 1 mark for "heat transfers from hot to cold", 1 mark for "reach same temperature/thermal equilibrium".

(d) Answer: The metal handle would become very hot and could burn the user's hand. (Metal is a good conductor of heat.)
Marks: 1 mark for "handle gets hot/burn risk", 1 mark for "metal conducts heat well" (or combined 1 mark for complete answer).

17.
(a) Answer: When the air inside the envelope is heated, it expands and becomes less dense than the cooler air outside. The less dense hot air rises, creating an upward buoyant force that lifts the balloon.
Marks: 1 mark for "air expands/less dense", 1 mark for "less dense than outside air", 1 mark for "buoyant force/upward force lifts balloon".

(b) Answer: The pilot should turn off the burner (or reduce the flame). This allows the air inside to cool down, become denser, and the buoyant force decreases, causing the balloon to descend.
Marks: 1 mark for "turn off/reduce burner", 1 mark for "air cools/becomes denser", 1 mark for "buoyant force decreases/balloon descends".

(c) Answer: As the outside air cools at night, it becomes denser. This increases the density difference between the inside (heated) air and outside air, increasing the buoyant force. The balloon would rise higher or require less burner use to stay afloat. If the burner is not used, the inside air also cools, and the balloon will eventually descend as the temperature difference decreases.
Marks: 1 mark for "outside air cools/becomes denser", 1 mark for "greater density difference/increased buoyancy", 1 mark for "balloon rises higher or needs less burner" (or "descends if burner off").

(d) Answer: The pilot must ensure there are no flammable materials near the burner, or must have a fire extinguisher on board, or must check for gas leaks before flight. (Any one valid safety precaution.)
Marks: 1 mark for any reasonable safety precaution related to burner/fire/gas.

18.
(a) Answer: A matt black surface absorbs more heat by radiation than a shiny white surface.
Marks: 1 mark

(b) Answer: (Any two) Volume of water (100 ml), initial temperature of water, distance from heat lamp, time of heating (10 minutes), size and shape of tins, type of thermometer, surrounding conditions.
Marks: 1 mark each for two correct variables.

(c) Answer: The matt black surface is a better absorber of radiant heat than the shiny white surface. It absorbs more heat from the heat lamp, transferring more heat to the water, causing a greater temperature rise. The shiny white surface reflects more radiation.
Marks: 1 mark for "black absorbs more heat/radiation", 1 mark for "white reflects more", 1 mark for "more heat transferred to water/higher temperature rise".

(d) Answer: Repeat the experiment multiple times and calculate the average temperature rise for each tin. (Or: Use more than one tin of each colour and take average.)
Marks: 1 mark for "repeat experiment" or "multiple trials" and "average".

19.
(a) Answer: Black surfaces are good absorbers of radiation. The black absorber plate absorbs maximum heat from the Sun's rays.
Marks: 1 mark for "good absorber of radiation", 1 mark for "absorbs maximum heat from Sun".

(b) Answer: Copper is a good conductor of heat. It quickly transfers the heat absorbed by the plate to the water flowing through the pipes.
Marks: 1 mark for "good conductor of heat", 1 mark for "quickly transfers heat to water".

(c) Answer: The glass cover allows sunlight (short-wave radiation) to pass through to the absorber plate but traps the longer-wave infrared radiation (heat) emitted by the hot plate, reducing heat loss by convection and radiation (greenhouse effect).
Marks: 1 mark for "lets sunlight in", 1 mark for "traps heat/reduces heat loss by convection and radiation".

(d) Answer: Insulation at the back reduces heat loss from the absorber plate to the surroundings by conduction and convection, ensuring more heat is transferred to the water in the pipes.
Marks: 1 mark for "reduces heat loss to surroundings", 1 mark for "by conduction/convection" or "more heat to water".

20.
(a) Answer: Heat transfers from the metal ball to the water. (From hotter object to colder object.)
Marks: 1 mark

(b) Answer: The metal ball is at a higher temperature than the water. Heat energy flows from the hotter ball to the cooler water, increasing the kinetic energy of the water molecules, which raises the water temperature.
Marks: 1 mark for "heat flows from hot to cold", 1 mark for "increases kinetic energy of water molecules/temperature rises".

(c) Answer: Plastic is a poor conductor of heat compared to metal. Heat transfers more slowly from the plastic ball to the water, so less heat is transferred in the same time, resulting in a smaller temperature rise.
Marks: 1 mark for "plastic is poor conductor", 1 mark for "slower heat transfer/less heat transferred in same time".

(d) Answer: The final temperature of the water will be lower than in the first experiment. With a larger mass of water, the same amount of heat from the ball is distributed among more water molecules, resulting in a smaller temperature increase per unit mass.
Marks: 1 mark for "lower final temperature", 1 mark for "same heat shared among more water molecules/smaller temperature rise per unit mass".

Marking Notes:

• For multi-mark questions, award partial marks for partially correct answers as indicated.
• Accept scientifically accurate alternative phrasing.
• Deduct marks for missing units where required (though not heavily tested in this quiz).
• Common misconceptions to watch for: "cold flows", "heat is a substance", "metal attracts cold", "vacuum 'sucks' heat".