Level 2 · Secondary physics teaching kit · Grades 10–12
Thermodynamics and statistical reasoning
Use the learner record during the live investigation, then use the instructor guide to facilitate comparison, address misconceptions, and assess evidence-bounded reasoning.
Learner lab record
Heat-engine boundary and efficiency ledger
How do reservoir temperatures and uncounted transfers constrain the useful work of a cyclic engine?
Setup
Use the heat-engine laboratory. Establish one complete hot-input, work-output, and cold-rejection ledger before changing either reservoir temperature.
Predict first
- 1. Predict the Carnot limit when both temperatures are equal.
- 2. Predict how raising only the hot temperature changes the ideal limit.
| Variable | Role | Unit |
|---|---|---|
| Hot reservoir temperature | independent | K |
| Cold reservoir temperature | independent | K |
| Heat input | controlled | J |
| Work, rejected heat, and efficiency | dependent | J and % |
Observation columns
Analyze
- 1. Does each run close Qh = W + Qc?
- 2. Which run approaches the ideal bound most closely?
- 3. Why is the Carnot value a ceiling rather than a promise?
- 4. Which stored-energy change could mimic cycle output?
Conclusion frame
For reservoirs at ___ K and ___ K, the engine delivered ___ J at ___% efficiency, compared with an ideal ceiling of ___%.
Instructor guide · 45–60 minutes
Teach the investigation, not the interface
Learning target: Learners close a cyclic energy ledger and distinguish measured efficiency from the reversible Carnot ceiling.
Prepare
- • Define heat into the engine as positive.
- • Draw hot reservoir, engine, and cold reservoir.
- • Prepare a run with an intentionally omitted rejected-heat term.
Facilitation moves
- • Require kelvin before computing a ratio.
- • Ask whether the device returned to its starting state.
- • Treat above-limit results first as boundary or measurement failures.
Accessibility and participation
- • Use a three-box energy-flow diagram with numeric labels.
- • Offer a unit-conversion reminder for Celsius to kelvin.
- • Let learners submit an annotated ledger instead of a long prose response.
Evidence of learning
- • A closed first-law ledger
- • A valid Carnot comparison
- • A clear complete-cycle boundary
Misconception checks
Efficiency below 100% means energy disappeared.
The remainder is rejected heat or another accounted transfer, not missing energy.
A fluctuation can power a passive one-reservoir cycle indefinitely.
Equilibrium fluctuations obey detailed balance; preparation, feedback, and resetting costs belong in the cycle.
Extension
Add a finite-rate loss model and explain the gap between reversible and practical efficiency.