Energy Transfers
4 marks · NormalThe diagram shows a cross-section of an external house wall constructed with two layers of brick and a cavity filled with insulation material.
Explain why the walls of modern houses are made with a cavity containing insulation material rather than being solid brick.
Name two ways that the cavity and the insulation reduce energy transfers from inside the house to outside, stating the method of energy transfer each affects.
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(a) The cavity reduces heat loss by trapping air (a poor conductor); insulation prevents both conduction through the wall and convection currents in the cavity, keeping heat inside better than solid brick.
(b) The cavity (with air or insulation) reduces conduction and stops convection currents in the gap. The foil surface on insulation can reflect radiation (infrared). (Any two correct, methods named.)
Common mistakes: Not stating energy transfer methods by name
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Marking points
B1 (a) · 1 mark · Mentions air cavity/insulation reduces conduction through walls.
B1 (a) · 1 mark · Mentions that insulation traps air/prevents convection currents in cavity.
B1 (b) · 1 mark · Identifies a method: reduces conduction OR stops convection.
B1 (b) · 1 mark · Names a second way: e.g., foil reflects radiation/insulation stops convection.
Worked solution
(a) The air space in the cavity is a poor conductor, reducing heat loss by conduction. Insulation materials further reduce heat transfer and stop air movement, preventing convection. Solid bricks would conduct more heat outwards.
(b) 1. Insulation reduces conduction (air is a poor conductor). 2. Insulation stops convection currents in the air gap. (Alternatively: Foil surfaces reflect infrared radiation, reducing loss by radiation.)