IGCSE Physics / Thermal energy
Reducing unwanted energy transfer
Edexcel International GCSE Physics (4PH1), chapter 15: Thermal energy, specification point 4.10. Free lesson.
Read the revision notes · IGCSE Physics past papers
Unwanted energy transfer can be reduced by trapping air, using a vacuum, or reflecting infrared radiation. Linking each insulating feature to the transfer it reduces helps you explain how homes and vacuum flasks stay warm.
How insulation reduces energy loss from a home
A house loses energy through its roof, walls, windows, gaps and floor. Many types of insulation work by trapping air. Air is a poor conductor, so it slows conduction. Trapped air cannot move freely to form convection currents, so it also reduces convection. Loft insulation uses fibres that trap air, reducing conduction and convection through the roof. Cavity wall insulation uses foam to trap air in the gap between two brick walls, reducing conduction and convection. Double glazing traps air or another gas between two panes of glass. The gas is a poor conductor, so it reduces…
How a vacuum flask reduces energy transfer
A vacuum flask is designed to reduce conduction, convection and radiation. Each part has a particular job, so explain the part and name the transfer it reduces. The space between the double glass walls is a vacuum, which has almost no particles. With no particles to transfer energy, conduction and convection cannot occur across it. The glass surfaces facing the vacuum are silvered like mirrors. They are poor emitters of infrared, so less energy leaves by radiation. They also reflect infrared back towards the drink. The stopper, usually plastic or cork, stops warm air…
Build a full explanation of the flask
For a longer answer, link each design feature to a named transfer and explain why it works. This makes clear how the flask keeps a hot drink hot.
Why fluffed feathers keep a bird warm
When a bird fluffs up its feathers, they trap more air. The trapped air is a poor conductor and cannot move to form convection currents, so less energy transfers from the bird to the surroundings.