Answer Key: Thermal Energy at School

Full credit for any reasonable notice + wonder. Ideal: Notice — "the metal feels colder than the wood." Wonder — "why do they feel different if the thermometer reads the same?" Accept any on-topic wonder. Science note (not required from students): metal conducts thermal energy away from the hand faster, so it feels colder even at equal temperature.

Accept any two real locations with a direction. Examples: a desk by a sunny window (warms), a shaded hallway (cooler), the cafeteria after cooking (warms), a stairwell in the morning (cool). More than one answer is defensible.

Radiation. Example from the diagram: the sun's rays passing through the window (sun → through window). This is the only mode that can cross empty space.

a) O — a directly measured value (48 °C).
b) I — it explains a cause ("because the sun heated it by radiation").
c) O — a directly measured value (24 °C).
d) I — a reasoned conclusion about why it is cooler.
Observation = measured/seen directly; inference = a conclusion reasoned from evidence.

The sunlit concrete absorbed radiation from the sun, raising its temperature; the shaded concrete received little direct sunlight. Accept any sentence naming radiation (sunlight) as the cause of the ~15 °C difference. Reject "conduction" as the primary cause here.

6a — A (Conduction). The can warms by direct contact with the metal rail.
6b — B (Convection). A fan moves warm air (a gas) around the room.
6c — C (Radiation). Sunlight (rays) warms the backpack.

Award full credit if the student names a valid mode and explains the mechanism. Worked examples:

• (i) Light-colored blinds: targets radiation. Blinds block/reflect incoming sunlight before it enters, so less radiant energy is absorbed inside. (Strongest choice — see Q8.)
• (ii) Fan: targets convection. Moving air mixes hot air away from students and speeds cooling; it does not stop energy from entering, so it helps less than blinds.
• (iii) Move desks to the far corner: uses the data (far corner air = 24 °C vs. near-window 27 °C). Reasonable, but it relocates students rather than reducing the heat entering — a weaker "fix."

Any of the three earns credit if the mode + mechanism are correct. Best-reasoned answer is (i).

Model answer. Claim: Light-colored blinds on the window would most reduce heat transfer into the classroom. Evidence: (1) In Table 1, sunlit surfaces were far hotter than shaded ones (sunlit concrete 44 °C vs. shaded 29 °C), showing sunlight adds a lot of energy. (2) In Figure 1, the sun's radiation enters through the window — the main path of energy into the room. Reasoning: Because the biggest energy input is radiation through the window, blocking it at the window stops the energy before it enters, unlike a fan (which only moves already-warmed air by convection).
Defensible alternates: A student may claim the fan is best if they argue convection removes built-up heat and cite Table 1's air readings; accept with sound reasoning, but the blinds argument is stronger because it addresses the source.

Articulate: accept any accurate plain-language definition of one mode (e.g., "conduction is heat moving through touch").
Connect: the cited row/part must actually match the chosen mode (e.g., metal handrail 48 °C → conduction/radiation; heating vent → convection; sun through window → radiation).
Extend: any correct new, out-of-school example (e.g., conduction — a spoon in soup; convection — boiling water; radiation — a campfire warming your face). More than one answer is defensible.