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Physics · 2.1.3 Gas pressure · Boyle's law · Paper 6

Gas Laws. Squeeze it.

Compress a fixed mass of gas at constant temperature and watch the pressure rise. Verify Boyle's law: pV = constant, so p ∝ 1/V. Switch to the pressure law to see how heating raises pressure at constant volume.

0625 Topic 2.1.3 — Gas pressure Boyle's law pV = const Paper 6 — ATP
Boyle's law — move the piston to change the volume at constant temperature. Watch pV stay constant.

Variables

40
20
1.0

Live readouts

Pressure p
101 kPa
Volume V
40 cm³
Temperature
293 K
pV (should be constant)
4040
Boyle's law: at constant temperature, p × V = constant for a fixed mass of gas.

Trial data

Record at five volumes (or temperatures) to test the law.

p vs 1/V — straight line ⇒ p ∝ 1/V

📋 Method (Cambridge ATP procedure)
  1. Trap a fixed mass of dry air in a sealed syringe/glass tube connected to a pressure gauge.
  2. Boyle's law: keep temperature constant; change the volume slowly (so no heating occurs) and record p for each V.
  3. Pressure law: keep the volume fixed; warm the gas in a water bath and record p at several temperatures.
  4. Compress slowly and wait before reading so the gas stays at room temperature.

Analytical control: plot p against 1/V (straight line through origin ⇒ pV = constant); or plot p against T in kelvin (straight line through origin ⇒ p ∝ T).

⚠ Sources of error & precautions
  • Compress slowly — fast compression heats the gas, breaking the constant-temperature condition.
  • No leaks — the mass of gas must stay fixed; check seals.
  • Read the gauge and volume scale perpendicular to avoid parallax.
  • For the pressure law, use absolute temperature in kelvin (°C + 273).
🎯 Syllabus reference (0625)
  • 2.1.3 Gases & the absolute scale of temperature — describe how a gas exerts pressure through molecular collisions; recall and use pV = constant at constant temperature; relate pressure and temperature for a fixed volume; use the kelvin scale.

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