Trace multiple thermal routes from a wood or coal fire
Explain conduction, rising hot gases and radiation in one stated fire account.
Extended only (Supplement); Physics 0625, 2026–2028, section 2.3.4. Core explains heating pans and room convection; Extended follows multiple significant routes in wood/coal fires and car radiators. Written explanations are self-checked
Before you begin
- Identify a chemical energy store and thermal transfers.
- Distinguish moving gases from electromagnetic radiation.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which route can warm a facing object outside the main hot-gas plume?
What you will learn
- Explain significant conduction, convection and radiation routes in a wood/coal fire.
- Distinguish chemical energy release from the transfer mechanisms that follow.
Separate the energy source from the paths
In a stated wood or coal fire, chemical energy is released by combustion and energy enters the hot fuel, gases and surroundings. Conduction within contacting solid fuel or supports can transfer energy toward other parts. Hot gas movement carries energy by convection, including a rising plume under suitable buoyancy conditions.
Infrared from hot fuel, flames and surroundings can reach a facing object without that object being in the rising gas stream. Very hot flame regions can also emit visible light; the presence of glow does not remove infrared. The routes can operate together, so one observed effect need not exclude the others.
Identify the observed location and boundary
An object beside a fire can receive substantial radiation while much hot gas moves upward. A solid support in contact with hot material can conduct, while gas flow through an opening can carry energy away. To interpret a particular temperature change, state its position, contacts and complete transfers rather than naming only 'fire heat'.
The diagram describes routes qualitatively. It does not establish a numerical share for each mechanism, a fuel efficiency or an exact temperature at a location. This is a written analysis of a supplied fire scenario, not instructions to start, modify or test a fire. Practical and specialist safety assessment remain separate.
Pause and explain
What explains energy passing along contacting hot solid fuel or supports?
Worked example
Explain why an object to one side of a fire can warm even when the main gas plume rises above it.
Show the worked solution
- The plume carries energy upward by convection.
- Infrared can travel from the hot source toward the side object.
- The object's absorption can increase its internal energy without requiring it to be in the plume.
Answer Radiation can warm the side object while convection carries hot gases upward.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Identify one conduction, one convection and one radiation route in the supplied fire example.
Give me a hint
Name the material or gap for each path.
Compare my reasoning
- Contacting solid fuel/supports can conduct.
- Rising hot gases carry energy by convection.
- Infrared reaches suitable absorbing surfaces across the surrounding space.
Solid contact conduction, hot-gas convection and infrared radiation.
Look for these in your work
- Use all three routes.
- Tie each to a concrete path.
Explain the side object's warming while hot gases mainly rise.
Give me a hint
Different routes can have different directions.
Compare my reasoning
- The plume transports energy upward.
- Radiation can travel toward the side object.
- Absorbed radiation can warm it even outside the main plume.
Radiation can explain the side warming without the same gas current reaching it.
Look for these in your work
- Name the appropriate route.
- Do not prohibit simultaneous convection.
A sketch labels all three routes but supplies no rates. Can you state that convection accounts for exactly 60% of the output?
Give me a hint
Qualitative paths do not supply numerical shares.
Compare my reasoning
- Three available routes are identified.
- No measured rates or complete numerical budget are given.
- An exact percentage cannot be calculated.
No exact mechanism percentage follows from the sketch.
Look for these in your work
- Use the diagram at its scope.
- Identify the missing rate evidence.
Common mistakes
- Combustion release and later transfer routes are different stages.
- A side object need not be in the hot-gas plume.
- No universal percentage shares are supplied.
What can you explain now?
Does a rising plume prevent radiation reaching a nearby side object?
Compare with the explanation
No.
Radiation can travel toward it while gas flows along a different route.
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Make it stick
Trace a fire's energy source and three simultaneous transfer routes without inventing shares or apparatus procedures.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.