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explain / describe / state
Recall and explain
A climber's sleeping bag is filled with fluffy fibres and has a metal zip. (a) Supplement. Explain, in terms of particles, why the air trapped between the fibres keeps the climber warm. (b) Describe an experiment, with two cans of hot water and a thermometer, to find out whether the sleeping-bag filling or a cotton sheet is the better thermal insulator. State what you measure, and how the result shows the better insulator. (c) Supplement. A pupil writes: “Energy travels along the metal zip because its atoms move from the warm end to the cold end.” Explain why this is incorrect. (d) Supplement. In the morning the climber holds three mugs of the same hot soup: a steel mug, a pottery mug and a plastic foam cup. State which feels hottest and which feels coolest to hold, and explain why.
explain: give reasons and connect them to evidence. describe: give the features or what happens. state: give a concise answer.
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Scope and sources
Cambridge IGCSE Physics 0625 · 2026–2028 v2 · Original learning materials.
Experiments that show good and bad thermal conductors (2.3.1.1); Supplement: conduction in solids by lattice vibrations and, in metals, by free electrons (2.3.1.2), why most liquids and gases conduct badly (2.3.1.3), and solids that conduct less well than good conductors but better than insulators (2.3.1.4); convection in liquids and gases, explained by density changes, with an experiment to show it (2.3.2.1, 2.3.2.2); everyday applications and consequences of conduction, convection and radiation, including heating a pan and heating a room (2.3.4.1). Thermal radiation and the vacuum flask are in Thermal radiation; conductivity numbers and rates are not covered.
Apparatus, amounts and times in the experiment are illustrative. Real practical work follows a teacher-approved safety method.
Official Cambridge syllabus