Exam-style question
Try this first
Which of the following best explains why a hot cup of tea cools down when left on a table?.
- A.The tea loses internal energy to the air until it reaches the same temperature as the air.
- B.The tea gains internal energy from the air until it reaches the same temperature as the air.
- C.The tea loses mass to the air until it reaches the same temperature as the air.
- D.The tea gains mass from the air until it reaches the same temperature as the air.
Model answer
What a good answer should say
- The tea loses internal energy to the air until it reaches the same temperature as the air.
Explanation
Why this works
Calculate reasoning: The rule is that heat flows from higher to lower temperature. Substitution: tea temperature > air temperature.
Working: Heat flows from tea to air, reducing tea's internal energy until temperatures equalise. Units: energy in J, temperature in °C/K.
Conclusion: tea cools by losing internal energy to the surrounding air.
Common mistake
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