| English | Pressure law |
|---|---|
| Bahasa Melayu | Hukum tekanan |
| 中文 | 压强定律 |
Definition
For a fixed mass of gas at constant volume, the pressure is directly proportional to its absolute temperature.
In exam terms
The pressure law (Gay-Lussac's law) states that for a fixed mass of gas at constant volume, the pressure is directly proportional to its absolute temperature. In symbols, p/T = constant, or p₁/T₁ = p₂/T₂, where p is pressure in pascals (Pa) and T is absolute temperature in kelvin (K).
Heating the gas makes its particles move faster, so they hit the walls both more often and harder, raising the pressure. The temperature must be in kelvin.
Worked line: p₁/T₁ = p₂/T₂ → (100 kPa)/(300 K) = p₂/(360 K), so p₂ = 120 kPa. Example of correct use: by the pressure law, heating a sealed rigid can raises the pressure inside it in proportion to its absolute temperature.
Do not confuse it with…
Do not confuse the pressure law with Charles's law. Both give a direct proportion to absolute temperature, but the pressure law keeps the volume constant (pressure against temperature), while Charles's law keeps the pressure constant (volume against temperature).
In Paper 2 this is usually asked as state the pressure law, a p against T calculation, or a graph. As with Charles's law, always convert the temperature to kelvin; a p against T graph in Celsius is a straight line that meets the temperature axis at about −273 °C.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)