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explain / state / calculate / describe
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explain: give reasons and connect them to evidence. state: give a concise answer. calculate: work out the answer from the data. describe: give the features or what happens.
Keep the lesson closed. (a) Explain how a gas exerts a pressure on the walls of its container. (b) State what is meant by the pressure of a gas, in terms of force. (c) A fixed mass of gas is squeezed into a smaller volume at a constant temperature. Explain, in terms of particles, why its pressure rises. (d) 80 cm³ of air at 100 kPa is squeezed slowly, at a constant temperature, to 50 cm³. Calculate its new pressure. (e) Describe the shape of the graph of p against V, and of p against 1/V, for a fixed mass of gas at a constant temperature.
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Scope and sources
Cambridge IGCSE Physics 0625 · 2026–2028 v2 · Original learning materials.
Gas pressure and changes in it from the motion of particles and their collisions with a surface (2.1.2.3), and pressure as the force of the collisions per unit area (2.1.2.7); the effect on the pressure of a fixed mass of gas of a change of temperature at constant volume and of a change of volume at constant temperature, in particle terms (2.1.3.1); converting between kelvin and degrees Celsius, T (in K) = θ (in °C) + 273 (2.1.3.2); pV = constant at constant temperature, with its graphs (2.1.3.3); thermal expansion of solids, liquids and gases at constant pressure, its uses and consequences, and why solids expand least and gases most (2.2.1.1–2.2.1.3). Absolute zero as the temperature of least particle motion and the particle model of matter are in PART01; pressure as force ÷ area and pressure in liquids are in PRES01.
Apparatus, amounts and times in the experiment are illustrative. Real practical work follows a teacher-approved safety method.
Official Cambridge syllabus