Aman keeps a plastic bottle, a wooden spoon and a metallic spoon in a closed…

Thermal equilibrium: when a set of objects is left together in a common surrounding for long enough, with no outside heat source or sink, heat keeps flowing between them and the surrounding air until every object reaches the same temperature as that surrounding and net heat flow stops. A material's thermal conductivity only decides how quickly it approaches that common temperature — a good conductor changes temperature faster than a poor conductor — it has no bearing on the temperature the object finally settles at.

Aman's plastic bottle, wooden spoon and metal spoon are all left in the same closed room, at 30°C, for an entire night — many hours, far longer than any of these small objects needs to finish exchanging heat with the room air. By morning, each object has stopped exchanging net heat with the air, i.e. each has independently reached the room's own temperature. Since T1, T2 and T3 are the readings on these three objects at that point, T1 = T2 = T3.

• T3 > T2 > T1 — This ranks the final readings by how fast each material conducts heat — metal fastest, wood in the middle, plastic slowest — as if conducting heat faster by itself leaves an object at a different final reading than a slower conductor. Conductivity governs the SPEED at which an object's own reading moves toward the surrounding air; consider whether a full night is enough time for even the slowest of these small objects to end up at a reading no different from the fastest one.

• T1 = T2 < T3 — This groups the plastic bottle and wooden spoon together as similarly slow conductors while assuming the metal spoon's much faster conductivity keeps its reading apart from the other two. Conductivity governs the SPEED at which an object's own reading moves toward the surrounding air; consider whether a full night is enough time for even the fastest of these small objects to end up at a reading no different from the slower ones.

• T1 > T2 > T3 — This ordering matches how touching each object FEELS rather than what a thermometer would show: metal feels the coolest to the skin because it carries heat away from a warm fingertip fastest, so it is tempting to rank the metal spoon as having the lowest actual reading. What the hand feels is the rate of heat leaving the skin into a good conductor — a different physical process from the object's own temperature after a full night in the same room air.

Hence the relation that holds after a full night in the same closed room is T1 = T2 = T3.