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state / explain
Recall and explain
A hot-water tank stands in a cupboard at room temperature. (a) State whether the cupboard walls emit infrared radiation. (b) The owner wants to keep the water in the tank hot. Explain whether the outside of the tank should be dull black or shiny. (c) Supplement. The tank is replaced by a larger one with the same surface, kept at the same temperature. Explain what happens to the rate at which the tank emits radiation.
state: give a concise answer. explain: give reasons and connect them to evidence.
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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