A-Level Physics Unit 5 January 2022 Paper Concepts Explained | A-Level物理 Unit 5 2022年1月试卷概念解析

📚 A-Level Physics Unit 5 January 2022 Paper Concepts Explained | A-Level物理 Unit 5 2022年1月试卷概念解析

This article breaks down the key physics concepts tested in the A-Level Unit 5 exam from January 2022. Covering thermodynamics, nuclear physics, and cosmology, it provides clear explanations to reinforce your understanding of the core principles.

本文解析2022年1月A-Level物理Unit 5试卷中考查的核心概念，涵盖热力学、核物理和宇宙学，通过清晰讲解巩固基本原理。

1. Ideal Gas Equation and Kinetic Theory | 理想气体方程与分子动理论

The ideal gas law links pressure p, volume V, amount of substance n, and absolute temperature T: pV = nRT, where R is the molar gas constant. Using the number of molecules N and Boltzmann constant k, it can also be written as pV = NkT.

理想气体状态方程将压强p、体积V、物质的量n和热力学温度T联系起来：pV = nRT，R为摩尔气体常数。若使用分子数N和玻尔兹曼常数k，则可表示为pV = NkT。

The kinetic theory model explains macroscopic properties via microscopic motion. The pressure of an ideal gas is p = ⅓ ρ⟨c²⟩, where ρ is density and ⟨c²⟩ is the mean square speed. The average translational kinetic energy per molecule is ½ m⟨c²⟩ = (3/2) kT, showing that temperature measures average molecular kinetic energy.

分子动理论模型通过微观运动解释宏观性质。理想气体的压强为p = ⅓ ρ⟨c²⟩，ρ为密度，⟨c²⟩为方均速率。每个分子的平均平动动能为½ m⟨c²⟩ = (3/2) kT，表明温度是分子平均动能的量度。

2. First Law of Thermodynamics | 热力学第一定律

The first law of thermodynamics is ΔU = Q + W, where ΔU is the change in internal energy, Q is heat added to the system, and W is work done on the system. When a gas expands and does work on its surroundings, W is negative.

热力学第一定律为ΔU = Q + W，ΔU是内能的变化，Q是系统吸收的热量，W是外界对系统做的功。气体膨胀对外做功时，W取负值。

For an ideal gas, internal energy depends only on temperature. In an isothermal process, ΔU = 0, so Q = −W; in an adiabatic process, Q = 0, so ΔU = W. These relationships are central to understanding heat engines.

理想气体的内能仅由温度决定。等温过程中ΔU = 0，故Q = −W；绝热过程中Q = 0，故ΔU = W。这些关系是理解热机的核心。

3. Specific Heat Capacity and Latent Heat | 比热容与潜热

Specific heat capacity c is the energy needed to raise the temperature of 1 kg of a substance by 1 K: c = ΔQ / (m Δθ). Specific latent heat L is the energy per kg required for a change of state at constant temperature: L = ΔQ / m, with L_f for fusion and L_v for vaporisation.

比热容c是使1 kg物质温度升高1 K所需的能量：c = ΔQ/(m Δθ)。比潜热L是单位质量物质在恒温下发生相变所需的能量：L = ΔQ/m，L_f为熔化潜热，L_v为汽化潜热。

In calculations, total heat transferred involving heating and a phase change is Q = m c Δθ + m L, where the latent heat term is added if the phase change occurs at constant temperature.

在涉及加热和相变的计算中，传递的总热量为Q = m c Δθ + m L，如果在恒温下发生相变，则需加上潜热项。

4. Nuclear Decay and Activity | 核衰变与活度

Radioactive decay is a random process governed by the decay constant λ (probability of decay per unit time). The activity A, measured in becquerels (Bq), is the number of decays per second: A = λN, with N the number of undecayed nuclei.

放射性衰变是一个随机过程，由衰变常量λ（单位时间衰变概率）描述。活度A以贝克勒尔（Bq）为单位，是每秒衰变次数：A = λN，N为未衰变核的数目。

5. Exponential Decay Law and Half-life | 指数衰变规律与半衰期

The number of radioactive nuclei N decreases exponentially with time t: N = N₀ e^(−λt). The half-life T½ is the time for N to halve, related to λ by T½ = ln 2 / λ.

放射性核的数目N随时间t指数衰减：N = N₀ e^(−λt)。半衰期T½是N减半所需的时间，满足T½ = ln2/λ。

The mass of a radioactive isotope follows the same law. An alternative form is N/N₀ = (1/2)^(t/T½), which can simplify calculations when time is given in multiples of half-lives.

放射性同位素的质量遵循相同规律。另一常用形式为N/N₀ = (1/2)^(t/T½)，当时间以半衰期倍数给出时可使计算简化。

6. Mass-Energy Equivalence | 质能等价

Einstein’s equation E = mc² shows that mass and energy are interchangeable. In nuclei, the mass defect Δm (difference between the total mass of separate nucleons and the mass of the nucleus) is converted into binding energy: ΔE = Δm c².

爱因斯坦方程E = mc²表明质量和能量可相互转化。原子核中，质量亏损Δm（孤立核子总质量与核质量之差）转化为结合能：ΔE = Δm c²。

Binding energy per nucleon indicates nuclear stability; it peaks around iron-56. This peak explains why energy is released in both fission of heavy nuclei and fusion of light nuclei.

比结合

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