Cambridge International AS & A Level · 14 · structured
Thermal equilibrium and the absolute-temperature limit
Thermal equilibrium and the absolute-temperature limit · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 7
- Topics
- 4
- Answer
- Complete
Two solid blocks A and B are placed in good thermal contact inside an insulated enclosure. Initially A is at 80 °C and B is at 20 °C. Neither undergoes a phase change.
- (a)
State the direction of net energy transfer by heating initially and the condition reached at thermal equilibrium.
2 marks - (b)
Must the two blocks have equal internal energies at thermal equilibrium? Explain.
1 mark - (c)
Explain how B's temperature rise relates to its internal energy.
2 marks - (d)
State absolute zero on the thermodynamic scale and its Celsius equivalent. Identify it as the lower temperature boundary in this syllabus model.
2 marks
Ready to self-mark?Reveal the detailed answer guide
(a)
State the direction of net energy transfer by heating initially and the condition reached at thermal equilibrium.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
Initially the hotter A transfers net energy by heating to the cooler B.
- 2
At equilibrium temperatures are equal; microscopic exchanges can continue but their net transfer is zero.
(b)
Must the two blocks have equal internal energies at thermal equilibrium? Explain.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
Internal energy depends on the amount and substance as well as temperature, so different blocks can share T without sharing U.
(c)
Explain how B's temperature rise relates to its internal energy.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
A temperature rise corresponds to more energetic random microscopic motion.
- 2
With no phase transition in this warming block, its internal energy increases; temperature is not the total energy of the whole block.
(d)
State absolute zero on the thermodynamic scale and its Celsius equivalent. Identify it as the lower temperature boundary in this syllabus model.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
Absolute zero is 0 K.
- 2
It corresponds to −273.15 °C and is the lowest thermodynamic temperature considered in the course.
Complete marking guidance
Use these worked steps alongside the part-by-part answers. They explain the method and mark allocation; they do not add extra marks.
- (a) Initially the hotter A transfers net energy by heating to the cooler B.
- (a) At equilibrium temperatures are equal; microscopic exchanges can continue but their net transfer is zero.
- (b) Internal energy depends on the amount and substance as well as temperature, so different blocks can share T without sharing U.
- (c) A temperature rise corresponds to more energetic random microscopic motion.
- (c) With no phase transition in this warming block, its internal energy increases; temperature is not the total energy of the whole block.
- (d) Absolute zero is 0 K.
- (d) It corresponds to −273.15 °C and is the lowest thermodynamic temperature considered in the course.
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