The shape of the lesson
By the end of the lesson, learners can
- Close every route: Switch the insulating features on and off and watch how each one cuts a different path for energy to escape.
- One device, three defences: Good insulation tackles all three transfer mechanisms, each with its own trick.
- Conduction: good conductors speed it; poor conductors and trapped air or a vacuum slow it.
- Convection: happens in fluids; a vacuum or trapped, still air stops it.
- Radiation: dull black speeds it; shiny silvered surfaces reflect and slow it.
One picture every idea returns to
Devices reduce or increase the transfer of thermal energy by acting on conduction, convection and radiation. Trapped air is a poor conductor that also cannot convect; shiny surfaces cut radiation; a vacuum blocks both conduction and convection.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Beating all three at once.. A vacuum flask is a small masterpiece of physics. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Close every route | Switch the insulating features on and off and watch how each one cuts a different path for energy to escape. Project tab 8 of the lab (Applications) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: One device, three defences | Good insulation tackles all three transfer mechanisms, each with its own trick. | Connect-Extend-Challenge |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 15 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in One device, three defences, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Connect-Extend-Challenge
After the new idea, each student writes three lines: how it connects to what they knew, how it extends their thinking, and what still challenges them. Pairs compare, then the challenges become the plenary.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| In a fibrous insulator it is the trapped air, not the material itself, that does the insulating. | Wool, foam and fibreglass work because they hold many small pockets of still air, which conducts poorly and cannot carry energy away by convection. |
Applications of thermal energy transfer: worksheet
6 questions, 15 marks. Written in the style of the papers; no past paper question is reproduced.
A saucepan has a metal base and a plastic handle. Explain why these two materials are chosen.
A vacuum flask keeps a drink hot. Explain how its design reduces heat loss by conduction, by convection, and by radiation.
A heating radiator is fixed near the floor of a room. Explain how it warms the whole room, and why a low position helps.
Explain how a fire in a building can spread by each of the three methods of thermal energy transfer.
Loft insulation is made of a thick, fluffy material that traps air. Explain how trapped air reduces heat loss from a house.
Energy from the Sun reaches the Earth across empty space. State which method of thermal energy transfer is responsible, and explain why it must be that one.
Answer key and marking notes
- The metal base is a good conductor, so energy passes quickly to the food. ✓
- The plastic handle is a poor conductor (insulator), so it stays cool enough to hold. ✓
- Conduction: the vacuum between the walls has almost no particles, so it cannot conduct. ✓
- Convection: there is no air in the vacuum to form convection currents, and the stopper seals the top. ✓
- Radiation: the silvered walls are poor emitters and reflect radiation back, reducing radiation loss. ✓
- Air heated at the radiator expands, becomes less dense and rises. ✓
- Cooler air sinks to replace it, setting up a convection current that circulates warm air around the room. ✓
- A low position lets the warmed air rise through the whole room; placed high, the warm air would stay trapped at the top. ✓
- Radiation: infrared crosses gaps and heats nearby objects until they catch alight. ✓
- Convection: hot gases rise and carry energy upward, spreading fire to higher levels. ✓
- Conduction: energy passes along metal beams, pipes and other materials to other rooms. ✓
- Air is a poor conductor, so trapped air greatly reduces heat loss by conduction. ✓
- Because the air is trapped and cannot move freely, it also cannot set up convection currents. ✓
- It must be radiation. ✓
- Space is a vacuum with no particles, and only radiation can transfer energy without a medium; conduction and convection both need a material. ✓
2 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
A vacuum flask keeps a drink hot. Which feature mainly reduces energy loss by radiation?
- AThe silvered, shiny walls.
- BThe vacuum between the walls.
- CThe narrow stopper at the top.
- DThe plastic outer case.
The cooling fins on the back of a refrigerator are painted matt black and have a large surface area. Why?
- ATo increase the rate at which energy is transferred away by radiation.
- BTo reduce the energy lost by the fridge.
- CTo make the fridge look attractive.
- DTo stop air from reaching the fins.
Quiz key
The silvered walls reflect thermal radiation back, cutting radiation losses. The vacuum stops conduction and convection, and the stopper reduces convection and evaporation, so those target different methods.
A large, matt black surface is an efficient emitter, so it radiates the unwanted thermal energy away quickly. The aim is to lose energy faster, not to reduce the loss (ruling out B).
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.