📚 IGCSE OCR Physics Thermal Physics Key Points | IGCSE OCR 物理：热力学 考点精讲
Thermal physics is a fundamental topic for IGCSE OCR Physics covering heat, temperature, energy transfer, changes of state and the behaviour of gases. Mastering these concepts is key to solving problems and scoring high marks in the exam.
热力学是IGCSE OCR物理的基础主题，涵盖热量、温度、能量传递、状态变化和气体行为。掌握这些概念对于解决问题并在考试中取得高分至关重要。
1. Temperature and Heat | 温度与热量
Temperature is a measure of the average kinetic energy of the particles in a substance. It is measured in degrees Celsius (°C) or kelvin (K). The kelvin scale is an absolute temperature scale, where 0 K is absolute zero (-273.15 °C).
温度是物质中粒子平均动能的量度。它以摄氏度（°C）或开尔文（K）为单位。开尔文温标是绝对温标，0 K 是绝对零度（-273.15 °C）。
Heat is the transfer of thermal energy from a region of higher temperature to a region of lower temperature. Heat flows until both regions reach thermal equilibrium, meaning they have the same temperature and no net energy transfer occurs.
热量是热能从较高温度区域向较低温度区域的传递。热量流动直到两个区域达到热平衡，即温度相同且没有净能量传递。
2. Heat Transfer Mechanisms | 热传递机制
Conduction: Heat transfer in solids through particle vibrations and free electron movement, without any bulk movement of the material. Metals are good conductors because they have free electrons; non-metals and gases are insulators.
传导：热量在固体中通过粒子振动和自由电子运动进行传递，没有物质的整体移动。金属因为有自由电子而成为良导体；非金属和气体是绝缘体。
Convection: Occurs in fluids (liquids and gases). Warmer, less dense fluid rises, while cooler, denser fluid sinks, creating convection currents. Convection requires a medium and cannot happen in a vacuum.
对流：发生在流体（液体和气体）中。较热、密度较小的流体上升，较冷、密度较大的流体下沉，形成对流循环。对流需要介质，不能在真空中发生。
Radiation: Transfer of energy by infrared electromagnetic waves. Radiation can travel through a vacuum. All objects emit and absorb thermal radiation. Dark, matte surfaces are good absorbers and emitters, while shiny, light surfaces are good reflectors.
辐射：通过红外电磁波传递能量。辐射可以在真空中传播。所有物体都在发射和吸收热辐射。深色粗糙表面是良好的吸收体和辐射体，而光亮浅色表面是良好的反射体。
3. Specific Heat Capacity | 比热容
The specific heat capacity (c) of a material is the energy required to raise the temperature of 1 kg of the substance by 1 °C (or 1 K). The formula linking energy, mass, specific heat capacity and temperature change is:
物质的比热容（c）是使1 kg 该物质温度升高1 °C（或1 K）所需的能量。能量、质量、比热容和温度变化之间的关系公式为：
E = m × c × ΔT
where E is energy transferred (J), m is mass (kg), c is specific heat capacity (J/(kg·°C)), and ΔT is the change in temperature (°C or K). Water has a very high specific heat capacity (4200 J/(kg·°C)), which makes it excellent for cooling systems and for moderating Earth's climate.
其中 E 是传递的能量（J），m 是质量（kg），c 是比热容（J/(kg·°C)），ΔT 是温度变化（°C 或 K）。水具有很高的比热容（4200 J/(kg·°C)），这使得它非常适合用于冷却系统以及调节地球气候。
The table below shows typical specific heat capacities for some common substances.
下表列出了一些常见物质的典型比热容。
| Substance | Specific heat capacity (J/(kg·°C)) |
|---|---|
| Water | 4200 |
| Aluminium | 900 |
| Copper | 385 |
| Iron | 450 |
4. Specific Latent Heat | 比潜热
Latent heat is the energy absorbed or released during a change of state at constant temperature. Specific latent heat (L) is the energy required to change the state of 1 kg of a substance without a change in temperature. The formula is:
潜热是物质在恒定温度下发生状态变化时吸收或释放的能量。比潜热（L）是使1 kg 物质在温度不变的情况下改变状态所需的能量。公式为：
E = m × L
Specific latent heat of fusion (Lf): energy needed to change 1 kg of solid to liquid at its melting point. For ice, Lf ≈ 334 000 J/kg.
熔化比潜热（Lf）：使1 kg固体在熔点时变为液体所需的能量。对于冰，Lf ≈ 334 000 J/kg。
Specific latent heat of vaporisation (Lv): energy needed to change 1 kg of liquid to gas at its boiling point. For water, Lv han the latent heat of fusion because extra energy is needed to separate particles completely.
汽化比潜热（Lv）：使1 kg液体在沸点时变为气体所需的能量。对于水，Lv ≈ 2 260 000 J/kg，比熔化潜热大得多，因为完全分离粒子需要额外的能量。
5. Thermal Expansion | 热膨胀
Most substances expand when heated because particles gain kinetic energy and move apart slightly. Solids expand a little, liquids expand more, and gases expand the most for the same temperature rise.
大多数物质受热膨胀，因为粒子获得动能并略微分开。固体膨胀较小，液体膨胀较大，气体在相同的温度升高下膨胀最大。
Applications include bimetallic strips in thermostats (different metals expand by different amounts, causing bending) and expansion gaps in bridges and railway lines. In liquid-in-glass thermometers, the liquid expands along the narrow tube.
应用包括恒温器中的双金属片（不同金属膨胀量不同导致弯曲），以及桥梁和铁轨的伸缩缝。在液体玻璃温度计中，液体沿着细管膨胀。
If expansion is restricted, large forces can develop. This is
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