📚 Measuring Gases | 气体的测量
In A-level physics, gases are described by measurable macroscopic quantities: pressure p, volume V, temperature T, and amount of substance n. Measuring these variables accurately is central to testing the gas laws and to using the ideal gas equation in practical situations.
在 A-level 物理中，气体由可测量的宏观量来描述：压强 p、体积 V、温度 T 和物质的量 n。准确测量这些变量是验证气体定律以及在实际情境中使用理想气体方程的核心。
1. Why Measuring Gases Matters | 为什么测量气体很重要
Gases are used as model systems because their macroscopic behaviour is relatively simple and can be linked directly to molecular motion. Accurate measurement of pressure, volume, temperature and amount of substance is therefore essential for testing the gas laws and determining quantities such as molar mass.
气体被用作模型系统，因为其宏观行为相对简单，并且可以直接与分子运动联系起来。因此，准确测量压强、体积、温度和物质的量对于验证气体定律以及确定摩尔质量等物理量至关重要。
2. State Variables and Units | 状态参量及其单位
Before taking any measurement, you must express all state variables in SI units. Pressure is in pascals (Pa), volume in cubic metres (m³), temperature in kelvins (K), and amount of substance in moles (mol). A common source of error is forgetting to convert °C to K or cm³ to m³.
在进行任何测量之前，必须将所有状态参量换算成国际单位制。压强单位为帕斯卡（Pa），体积单位为立方米（m³），温度单位为开尔文（K），物质的量单位为摩尔（mol）。常见的错误来源是忘记将 °C 转换为 K，或将 cm³ 转换为 m³。
| Quantity / 量 | SI unit / 国际单位 | Common conversion / 常用换算 |
| pressure p / 压强 | Pa | 1 atm = 1.01 × 10⁵ Pa; 1 kPa = 10³ Pa |
| volume V / 体积 | m³ | 1 m³ = 10⁶ cm³ = 10³ dm³ |
| temperature T / 温度 | K | T (K) = θ (°C) + 273.15 |
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