📚 Physical Quantities and Units | 物理量与单位
Welcome to this CIE A-Level Physics revision guide on ‘Appendix 1: Physical Quantities and Units’. A clear understanding of base units, derived units, prefixes and dimensional checks is essential for every topic in the syllabus, from mechanics to electricity and thermal physics. This guide explains the key ideas with bilingual explanations and exam-focused examples.
欢迎阅读本篇 CIE A-Level 物理复习指南，主题为“附录 1：物理量与单位”。清晰理解基本单位、导出单位、前缀和量纲检验，对于大纲中从力学到电学、热物理的每个主题都至关重要。本指南通过中英双语讲解和考试导向的示例来阐释关键概念。
1. The Language of Measurement | 测量的语言
In physics, a physical quantity is any property of matter or energy that can be measured. It is expressed as the product of a numerical value and a unit.
在物理学中，物理量是物质或能量中任何可以被测量的属性。它表示为数值与单位的乘积。
For example, writing ‘length = 5.0 m’ means the length is five times the standard metre. The unit defines the scale of the measurement.
例如，写“长度 = 5.0 m”表示长度是标准米的五倍。单位定义了测量的尺度。
The SI system provides a coherent set of base units from which all other units are derived. This avoids confusion between different systems such as imperial or cgs units.
国际单位制提供了一套相互一致的基本单位，所有其他单位都由它们导出。这避免了不同单位制（如英制或 cgs 制）之间的混淆。
2. SI Base Quantities and Units | SI 基本量与基本单位
The seven SI base quantities and their standard units are shown below. Learn these exactly, including the correct symbols and case.
七个 SI 基本量及其标准单位如下表所示。务必准确记忆这些内容，包括正确的符号和大小写。
| Base Quantity | 基本量 | Unit | 单位 | Symbol | 符号 |
|---|---|---|
| Length | 长度 | metre | 米 | m |
| Mass | 质量 | kilogram | 千克 | kg |
| Time | 时间 | second | 秒 | s |
| Electric current | 电流 | ampere | 安培 | A |
| Thermodynamic temperature | 热力学温度 | kelvin | 开尔文 | K |
| Amount of substance | 物质的量 | mole | 摩尔 | mol |
| Luminous intensity | 发光强度 | candela | 坎德拉 | cd |
Note that the kilogram is the only base unit with a prefix. Its symbol is always lowercase ‘kg’.
注意，千克是唯一带有前缀的基本单位，其符号始终为小写 “kg”。
3. Derived Quantities and Special Units | 导出量与专用单位
Derived quantities are formed by combining base quantities through multiplication or division. For example, speed is length divided by time, so its unit is m s⁻¹ (metres per second).
导出量是通过基本量的乘除组合形成的。例如，速度是长度除以时间，因此其单位为 m s⁻¹（米每秒）。
Several derived units have been given special names to simplify expression. The table lists common examples required in CIE Physics.
一些导出单位被赋予专门名称以简化表达。下表列出了 CIE 物理中常见的例子。
| Quantity | 物理量 | Unit name | 单位名称 | Symbol | 符号 | Base unit equivalent | 基本单位表示 |
|---|---|---|---|
| Force | 力 | newton | 牛 | N | kg m s⁻² |
| Pressure | 压力 | pascal | 帕 |
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