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Physics notebook Cambridge IGCSE 0625

Independent final check

Explain without the key

explain / show / calculate / describe / state

Final check

explain: give reasons and connect them to evidence. show: use the given information. calculate: work out the answer from the data. describe: give the features or what happens. state: give a concise answer.

The graph shows how the pressure of the air in a sealed syringe changes with its volume, at a constant temperature. (a) Explain, in terms of particles and the force on each unit of area, why the pressure at B is higher than at A. (b) Use the values at A and B to show that pV is constant. (c) Calculate the volume of the air when its pressure is 150 kPa. (d) Describe the graph you would get by plotting p against 1/V for these readings. (e) State the two conditions needed for pV to stay constant.

Graph of pressure against volume for the air in a sealed syringe kept at a constant temperature, from 0 to 70 cm³ and 0 to 350 kPa. The orange curve falls steeply at small volumes and gets flatter at large ones. Point A is at 60 cm³ and 100 kPa; point B is at 20 cm³ and 300 kPa. (enlarge)
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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