Describe an air convection demonstration
Trace rising air near a heater and cooler replacement flow without saying the source makes air heavier.
Core and Extended; Physics 0625, 2026–2028, section 2.3.2. Convection in liquids and gases, density changes and described demonstrations are Core requirements. Written explanations and supplied data are self-checked
Before you begin
- Explain fluid density changes under permitted expansion.
- Identify bulk airflow and a complete circulation path.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Where is rising outflow expected in the supplied open chamber?
What you will learn
- Describe a gas demonstration of convection.
- Explain a teacher-approved tracer route through a heated and cooler opening.
Use a suitable controlled chamber
In a teacher-supervised demonstration, a suitable transparent chamber has two vertical openings and an approved electric warming source below one opening. An appropriate teacher-approved visible tracer reveals air movement near the other opening. The setup remains suitably open to airflow and is used under the laboratory procedure, rather than as a sealed pressure vessel.
Air near the warmer opening can expand, become less dense and rise out. Cooler replacement air can enter through the other opening and move through the chamber toward the warmed region. The tracer helps reveal that gas path. The illustrated arrows are one supplied arrangement; source position, openings and surrounding currents affect actual results.
Interpret flow rather than assume a room-temperature uniformity
The visible tracer is suspended material carried by air; it is not the air molecules themselves enlarged to visible size. Its movement supports a bulk route when other drafts and imposed fan flows are controlled. A heater above the observation region or a strong external draft can change the flow, so document conditions.
Air heated in a rigid fixed-volume container has different constraints and can show a pressure response rather than the same open expansion route. Do not transplant the chamber explanation without its openings. Written tracer analysis does not establish safe apparatus use or practical-assessment competence.
Pause and explain
What is the visible tracer in this air experiment?
Worked example
In a supplied two-opening chamber, tracer enters the cooler opening and exits above the electric heater. Explain the movement.
Show the worked solution
- Air near the heater warms and can expand.
- Its lower density promotes rise through the warmed opening.
- Cooler replacement air enters the other opening and carries the tracer across the chamber.
Answer Density-driven airflow rises at the heated opening with cooler replacement flow through the other.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
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.
Describe the two-opening air demonstration and expected flow.
Give me a hint
Track the warmed outlet and cooler replacement inlet.
Compare my reasoning
- Use a suitable open chamber, approved electric heater and teacher-approved tracer.
- Observe rising air above the warmed region.
- Observe cooler air entering the other opening and moving toward that region.
Rising warmed outflow with a cooler replacement path.
Look for these in your work
- Specify the open arrangement.
- Trace the full route.
Explain the density change in air near the heater and what the tracer represents.
Give me a hint
Use retained mass and permitted expansion.
Compare my reasoning
- The warmed air can expand at the stated conditions.
- Its density decreases and it can rise.
- The visible tracer is carried suspended material, not air molecules.
Lower-density warmed air rises; suspended tracer follows the bulk flow.
Look for these in your work
- Use the correct density direction.
- Distinguish the tracer scale.
A fan blows through the chamber during the demonstration. What limitation does that introduce, and how would you improve attribution?
Give me a hint
Forced airflow can obscure natural circulation.
Compare my reasoning
- The fan imposes another bulk-flow cause.
- The tracer path no longer isolates heating-driven density circulation.
- Control external drafts and compare suitable heater conditions under the teacher's plan.
Control forced drafts before attributing the observed route to natural convection alone.
Look for these in your work
- Identify the confounder.
- Preserve the practical supervision limit.
Common mistakes
- The visible tracer is not individual air molecules.
- Include the replacement route.
- An open chamber and a rigid sealed-volume model have different constraints.
What can you explain now?
Does heating the air make its density increase in the permitted-expansion model?
Compare with the explanation
No.
For a retained mass, greater volume gives lower density.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain a gas demonstration with permitted expansion, buoyant outflow and cooler replacement, keeping tracer and evidence limits clear.
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.