Mastering Thermal Physics for CIE A-Level: Temperature, Ideal Gases and the First Law | 精通 CIE A-Level 热学：温度、理想气体与热力学第一定律

📚 Mastering Thermal Physics for CIE A-Level: Temperature, Ideal Gases and the First Law | 精通 CIE A-Level 热学：温度、理想气体与热力学第一定律

Thermal physics links microscopic molecular motion to macroscopic measurable quantities such as temperature, pressure, internal energy and heat transfer. In CIE A-Level Physics, candidates must be able to move confidently between the ideal gas equation, the kinetic theory model and the first law of thermodynamics, and to explain practical methods for specific heat capacity and latent heat.

热学将微观分子运动与温度、压强、内能和热量传递等宏观可测量联系起来。在 CIE A-Level 物理中，考生需要能够在理想气体方程、气体动理论模型和热力学第一定律之间自如切换，并能解释比热容和潜热的实验方法。

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1. Temperature and Thermal Equilibrium | 温度与热平衡

Temperature is a macroscopic property that determines the direction of net heat transfer between two objects. Two bodies are in thermal equilibrium when there is no net energy transfer between them, which means their temperatures are equal.

温度是决定两物体之间净热传递方向的宏观物理量。当两物体之间没有净能量传递时，它们处于热平衡，这意味着它们的温度相同。

The zeroth law of thermodynamics formalises this idea: if object A is in thermal equilibrium with object C, and object B is also in thermal equilibrium with C, then A and B are in thermal equilibrium with each other. This allows temperature to be used as a consistent physical quantity.

热力学第零定律将这一概念形式化：若物体 A 与物体 C 热平衡，物体 B 也与 C 热平衡，则 A 与 B 彼此也处于热平衡。这使得温度可以作为一个一致的物理量使用。

In CIE questions, thermal equilibrium is often used to explain why a thermometer must be left in contact with a substance until the reading becomes steady. At that moment the thermometer, the substance and the surroundings are all at the same temperature.

在 CIE 考题中，热平衡常被用来解释为什么温度计必须与被测物质接触，直到读数稳定。此时温度计、被测物质和周围环境都处于同一温度。

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2. Temperature Scales and Thermometers | 温标与温度计

The Celsius scale uses the ice point (0 °C) and steam point (100 °C) at standard atmospheric pressure as fixed points, divided into 100 equal intervals. The thermodynamic Kelvin scale is independent of any material property; its unit is the kelvin, K.

摄氏温标以标准大气压下的冰点（0 °C）和汽点（100 °C）为固定点，分为 100 等份。热力学开尔文温标不依赖于任何物质特性，其单位为开尔文 K。

The conversion is T(K) = θ(°C) + 273.15. A change of 1 °C is exactly equal to a change of 1 K, which is why kelvin is preferred in all gas law and kinetic theory calculations.

换算关系为 T(K) = θ(°C) + 273.15。1 °C 的温度变化恰好等于 1 K，因此所有气体定律和动理论计算中都优先使用开尔文。

A liquid-in-glass thermometer relies on the expansion of a liquid with temperature, while a thermocouple uses the e.m.f. generated at a junction of two different metals. Thermocouples have a small thermal capacity and can measure rapidly changing temperatures, but they require calibration against known temperatures.

液体温度计依靠液体随温度膨胀，而热电偶利用两种不同金属结点处产生的电动势。热电偶热容小，可以测量快速变化的温度，但需要使用已知温度进行校准。

Absolute zero, 0 K, is the lowest possible temperature. At this temperature particles have the minimum possible internal energy; it is the temperature at which the pressure of an ideal gas would become zero according to extrapolation of the pressure law.

绝对零度 0 K 是最低可能温度。在该温度下粒子具有最小的内能；根据压强定律外推，它是理想气体压强变为零的温度。

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3. Kinetic Model of Matter | 物质动理论模型

The kinetic model describes matter as made of particles in constant motion. In solids, particles vibrate about fixed positions; in liquids, they can slide past one another; in gases, they move freely and rapidly in random directions.

动理论模型将物质描述为由不断运动的粒子组成。固体中粒子在固定位置附近振动；液体中粒子可以相互滑动；气体中粒子自由快速地向各个方向无规则运动。

Brownian motion of smoke particles in air provides direct evidence for the random motion of gas molecules. The larger smoke particles are bombarded unevenly by invisible air molecules, causing observable irregular movement.

空气中烟雾粒子的布朗运动为气体分子的无规则运动提供了直接证据。较大的烟雾粒子受到不可见空气分子的不均匀撞击，从而产生可观察的无规则运动。

Temperature is a measure of the average random kinetic energy of particles. Higher temperature means greater average kinetic energy, but individual molecules still have a wide range of speeds because collisions continually redistribute energy.

温度是粒子平均无规则动能的量度。温度越高，平均动能越大，但由于碰撞不断重新分配能量，单个分子仍然具有很宽的速度分布。

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4. Internal Energy | 内能

Internal energy is the sum of the randomly distributed kinetic energy and the intermolecular potential energy of all particles in a system. It excludes kinetic energy of the bulk motion of the object and potential energy due to external fields such as gravity.

内能是系统内所有粒子的无规则分布动能与分子间势能之和。它不包括物体整体运动的动能和由重力等外场引起的势能。

During a change of state at constant temperature, the kinetic energy of particles does not change, but their potential energy increases when bonds are broken. Therefore the internal energy increases even though the temperature remains constant.

在恒温相变过程中，粒子的动能不变，但断键时势能增加。因此即使温度保持不变，内能也增加。

For an ideal gas, there are no intermolecular forces between collisions, so the internal energy depends only on the total random kinetic energy of the molecules. This means the internal energy of an ideal gas is directly proportional to its absolute temperature.

对于理想气体，碰撞之间不存在分子间作用力，因此内能只取决于分子的总无规则动能。这意味着理想气体的内能与其绝对温度成正比。

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5. Specific Heat Capacity | 比热容

Specific heat capacity c is the energy required to raise the temperature of 1 kg of a substance by 1 K. The equation is Q = mcΔθ, where Q is heat energy, m is mass and Δθ is temperature change.

比热容 c 是使 1 kg 物质温度升高 1 K 所需的能量。公式为 Q = mcΔθ，其中 Q 为热量，m 为质量，Δθ 为温度变化。

Q = mcΔθ

In a typical experiment, an electrical heater supplies energy E = Pt = VIt

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