Contents
Independent final check
Explain without the key
state / explain / describe
Final check
(a) State what kind of radiation thermal radiation is. (b) Explain why energy from the Sun can reach the Earth by radiation but not by conduction or convection. (c) Describe how the colour and texture of a surface affect how well it emits infrared radiation. (d) Supplement. Describe an experiment with a Leslie cube to compare how well different surfaces emit infrared. Say what you keep the same and what you measure. (e) Supplement. Besides its colour and texture, state two things that affect the rate at which a surface emits radiation.
state: give a concise answer. explain: give reasons and connect them to evidence. describe: give the features or what happens.
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Scope and sources
Cambridge IGCSE Physics 0625 · 2026–2028 v2 · Original learning materials.
Thermal radiation as infrared radiation, which all objects emit (2.3.3.1), and which needs no medium (2.3.3.2); the effect of surface colour (black or white) and texture (dull or shiny) on emitting, absorbing and reflecting infrared (2.3.3.3); Supplement: the energy balance of an object at constant temperature (2.3.3.4), and what happens when it receives energy faster or slower than it transfers energy away (2.3.3.5); the Earth’s temperature and the factors that control its balance of incoming and emitted radiation, such as greenhouse gases and ice (2.3.3.6); experiments to tell good and bad emitters (2.3.3.7) and absorbers (2.3.3.8) of infrared; how the rate of emission depends on surface temperature and surface area (2.3.3.9); applications where more than one transfer matters: a fire burning wood or coal and a radiator in a car (2.3.4.2), and also a vacuum flask. Conduction and convection are in Conduction and convection; the electromagnetic spectrum and wavelengths of infrared are in a later module.
Apparatus, amounts and times in the experiment are illustrative. Real practical work follows a teacher-approved safety method.
Official Cambridge syllabus