📚 Year 12 CCEA Physics: Core Concepts Review | Year 12 CCEA 物理：核心知识点梳理
This article provides a systematic overview of the essential concepts covered in Year 12 CCEA AS Physics, including mechanics, materials, waves, electricity, quantum phenomena and astronomy. Each topic is broken down into key formulas, definitions and exam-focused explanations to help you consolidate your understanding and prepare effectively.
本文系统梳理了 Year 12 CCEA AS 物理课程的核心知识点，涵盖力学、材料、波、电学、量子现象与天文学。每个主题均提炼出关键公式、定义与应试要点，帮助你高效整合知识、有的放矢地备考。
1. Physical Quantities and Units | 物理量与单位
All physical quantities are expressed in SI base units: the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol) and candela (cd). Prefixes from pico (10⁻¹²) to tera (10¹²) are used to simplify numerical values, and derived units such as the newton (N) or joule (J) are expressed in terms of base units.
所有物理量都用国际单位制的基本单位表示：米（m）、千克（kg）、秒（s）、安培（A）、开尔文（K）、摩尔（mol）和坎德拉（cd）。常用词头从皮（10⁻¹²）到太（10¹²）简化数值书写，导出单位如牛顿（N）或焦耳（J）均可用基本单位表示。
You must be able to check the homogeneity of equations by substituting base units on both sides, and use prefixes to convert between units when plotting graphs or calculating quantities. Estimation of physical magnitudes, such as the mass of an apple (~0.1 kg) or the wavelength of visible light (~5 × 10⁻⁷ m), is also examined.
你需要掌握通过代入基本单位来检验方程两侧的单位一致性，并运用词头在作图或计算时进行单位换算。对常见物理量大小的估算，如一个苹果的质量约为 0.1 kg、可见光波长约为 5 × 10⁻⁷ m，也是考查点。
2. Scalars, Vectors and Moments | 标量、矢量与力矩
Scalars have magnitude only (e.g. mass, temperature, energy), while vectors possess both magnitude and direction (e.g. displacement, velocity, force). Vector addition is performed using tip-to-tail diagrams or resolution into perpendicular components, often with trigonometry.
标量只有大小（如质量、温度、能量），矢量既有大小又有方向（如位移、速度、力）。矢量相加可采用三角形法则或正交分解法，常结合三角运算。
The principle of moments states that for a body in rotational equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments about any pivot. This enables calculation of unknown forces in levers and beams. A couple consists of two equal and opposite parallel forces, producing a torque of magnitude F × d, where d is the perpendicular distance between the forces.
力矩原理指出，对转轴作旋转平衡的物体，顺时针力矩之和等于逆时针力矩之和。由此可计算杠杆与横梁中的未知力。力偶是一对大小相等、方向相反的平行力，产生的转矩大小为 F × d，其中 d 为两力之间的垂直距离。
3. Linear Motion and Graphs | 直线运动与图像
The three SUVAT equations—v = u + at, s = ut + ½at² and v² = u² + 2as—describe uniform acceleration along a straight line. The fourth equation s = ½(u + v)t is useful when time is known. These apply only when acceleration is constant.
三个匀变速直线运动公式——v = u + at、s = ut + ½at² 和 v² = u² + 2as——描述了匀加速直线的运动规律。当时间已知时，第四条公式 s = ½(u + v)t 也十分便捷。上述公式只适用于加速度恒定的情形。
Displacement–time graphs give velocity as the gradient, while velocity–time graphs give acceleration as the gradient and displacement as the area under the graph. Interpreting these graphs is crucial for describing motion, including instantaneous rest and changing direction.
位移–时间图中斜率代表速度；速度–时间图中斜率代表加速度，图线下的面积代表位移。准确解读这些图像对于描述运动状态至关重要，包括瞬时静止和改变运动方向等情况。
4. Dynamics and Newton’s Laws | 动力学与牛顿定律
Newton’s first law: an object remains at rest or in uniform motion unless acted on by a resultant force. Newton’s second law: F = ma relates resultant force, mass and acceleration. Newton’s third law: when two bodies interact, the forces they exert on each other are equal in magnitude and opposite in direction, but act on different bodies.
牛顿第一定律：若物体不受外力或所受合力为零，将保持静止或匀速直线运动状态。牛顿第二定律：F = ma 将合力、质量与加速度联系在一起。牛顿第三定律指出，两物体相互作用时，彼此施加的力大小相等、方向相反，但分别作用在不同物体上。
Terminal velocity occurs when the drag force balances the weight, resulting in zero acceleration. Free‑body diagrams help identify all forces acting on an object, such as weight, normal contact force, tension and friction, allowing the resultant force to be calculated along chosen directions.
当阻力等于重力时，物体达到终极速度，加速度为零。受力分析图可帮助标出所有作用力，如重力、法向接触力、张力和摩擦力，进而沿选定方向计算合力。
5. Work, Energy and Power | 功、能与功率
Work done by a constant force is W = Fs cos θ, where θ is the angle between the force and displacement. Energy is the capacity to do work and is always conserved. Kinetic energy Eₖ = ½mv², and gravitational potential energy change ΔEₚ = mgΔh.
恒力做功 W = Fs cos θ，其中 θ 为力与位移的夹角。能量是做功的本领，总量守恒。动能 Eₖ = ½mv²，重力势能变化量 ΔEₚ = mgΔh。
Principle of conservation of energy: in a closed system, energy can be transferred between stores but the total remains constant. Power is the rate of energy transfer, P = W/t or P = Fv for constant velocity. Efficiency is useful output energy divided by total input energy.
能量守恒原理指出，在封闭系统中，能量仅在储存形式间传递，总量不变。功率是能量传递的速率，P = W/t，对匀速运动可用 P = Fv。效率为有用输出能量与总输入能量之比。
6. Deformation of Solids | 固体的形变
Hooke’s law: F = kx, where k is the spring constant. This is valid only up to the limit of proportionality. Beyond the elastic limit, plastic deformation occurs and the material does not return to its original shape. The area under a force–extension graph represents work done.
胡克定律：F = kx，其中 k 为劲度系数，仅在线性比例极限内成立。超过弹性极限后发生塑性变形，材料无法恢复原状。力–伸长图下的面积表示外力做的功。
Stress is defined as σ = F/A and strain as ε = ΔL/L. The Young modulus E = σ/ε describes the stiffness of a material and is measured in pascals (Pa). Stress–strain graphs help identify brittle, ductile and polymeric behaviour.
应力 σ = F/A，应变 ε = ΔL/L。杨氏模量 E = σ/ε 表征材料的刚度，单位为帕斯卡（Pa）。应力–应变图可用于辨别脆性、延展性和高分子材料的不同行为。
7. Electric Circuits and Potential Dividers | 电路与分压器
Current is the rate of flow of charge, I = ΔQ/Δt. Potential difference is the energy transferred per unit charge, V = W/Q. Ohm’s law V = IR applies for ohmic conductors at constant temperature. Resistance in series: Rₛ = R₁ + R₂ + …; in parallel: 1/Rₚ = 1/R₁ + 1/R₂ + …
电流是电荷流动的速率，I = ΔQ/Δt；电势差是单位电荷传递的能量，V = W/Q。欧姆定律 V = IR 适用于恒温下的欧姆导体。串联电阻：Rₛ = R₁ + R₂ + …；并联电阻：1/Rₚ = 1/R₁ + 1/R₂ + …
A potential divider produces a fraction of the input voltage: Vₒᵤₜ = Vᵢₙ × R₂/(R₁ + R₂). This circuit is widely used with sensors such as thermistors and LDRs to produce a varying output in light‑ or temperature‑sensing applications. The internal resistance r of a source reduces terminal p.d.: V = ε – Ir.
分压器可输出输入电压的一部分：Vₒᵤₜ = Vᵢₙ × R₂/(R₁ + R₂)。该电路常与热敏电阻或光敏电阻等传感器配合，用于感光或温控场合中输出可变电压。电源内阻 r 会降低路端电压：V = ε – Ir。
8. Waves and Refraction | 波与折射
A progressive wave transfers energy without transferring matter. The wave equation v = fλ links speed, frequency and wavelength. Transverse waves (e.g. light) have oscillations perpendicular to direction of travel; longitudinal waves (e.g. sound) have oscillations parallel to it.
行波传播能量而不传播物质。波动方程 v = fλ 联系了波速、频率和波长。横波（如光）的振动方向与传播方向垂直；纵波（如声波）的振动方向与传播方向平行。
Refraction is governed by Snell’s law: n₁ sin θ₁ = n₂ sin θ₂. The absolute refractive index of a material is n = c/v. Total internal reflection occurs when the angle of incidence exceeds the critical angle c, given by sin c = 1/n (for light leaving the denser medium). This principle underpins fibre optics.
折射遵循斯涅耳定律：n₁ sin θ₁ = n₂ sin θ₂。材料的绝对折射率 n = c/v。当入射角大于临界角 c 时发生全内反射，sin c = 1/n（针对光离开光密介质的情况）。光纤通信正是依赖该原理。
9. Superposition, Interference and Diffraction | 叠加、干涉与衍射
The principle of superposition states that when two waves meet, the resultant displacement is the vector sum of their individual displacements. Constructive interference yields a maximum when the path difference is nλ; destructive interference yields a minimum when the path difference is (n + ½)λ.
叠加原理指出，两列波相遇时，合位移是各列波位移的矢量和。当路程差为波长的整数倍 nλ 时，发生相长干涉产生极大；当路程差为 (n + ½)λ 时，发生相消干涉产生极小。
Young’s double‑slit experiment demonstrates interference of light, with fringe width Δy = λD/d, where D is the slit‑to‑screen distance and d the slit separation. Diffraction gratings produce sharper maxima according to d sin θ = nλ. Single‑slit diffraction also shows a central maximum flanked by dimmer fringes.
杨氏双缝实验展示了光的干涉，条纹间距 Δy = λD/d，其中 D 为缝到屏的距离，d 为双缝间距。衍射光栅依据 d sin θ = nλ 产生更锐利的明纹。单缝衍射则呈现中央最亮、两侧逐渐减弱的条纹图样。
10. Quantum Physics and Wave–Particle Duality | 量子物理与波粒二象性
The photon model describes light as packets of energy, E = hf, where h is the Planck constant. The photoelectric effect demonstrates that electrons are emitted from a metal surface only when the incident frequency exceeds the threshold frequency. The kinetic energy of emitted electrons is Eₖₘₐₓ = hf – φ, where φ is the work function.
光子模型将光描述为能量子，E = hf，其中 h 为普朗克常量。光电效应表明，只有当入射光频率超过截止频率时，电子才从金属表面逸出。光电子的最大动能 Eₖₘₐₓ = hf – φ，其中 φ 为逸出功。
Wave–particle duality is expressed by the de Broglie wavelength λ = h/p, applying to all matter. Electron diffraction provides evidence that particles possess wave‑like properties, reinforcing that light and matter both exhibit dual behaviour.
波粒二象性通过德布罗意波长 λ = h/p 体现，适用于一切实物粒子。电子衍射实验证实了粒子也具有波动性，进一步说明光和物质都表现出双重属性。
11. Astronomical Concepts | 天文概念
The parsec is the distance at which a star has a parallax angle of one arcsecond: d (pc) = 1/p (arcsec). The Hertzsprung–Russell diagram plots absolute magnitude against temperature or spectral class, revealing distinct groupings such as the main sequence, red giants and white dwarfs.
秒差距是视差角为 1 角秒的恒星距离：d (pc) = 1/p (arcsec)。赫罗图以绝对星等对温度或光谱型作图，展现出主序星、红巨星和白矮星等不同星族。
Stars evolve from protostars to main sequence, then to red giants and ultimately to white dwarfs, neutron stars or black holes depending on their mass. Wien’s displacement law λₘₐₓ T = constant and the Stefan–Boltzmann law link a star’s surface temperature to its colour and luminosity, enabling classification and distance estimation.
恒星从原恒星演化到主序阶段，再成为红巨星，最终根据质量演变成白矮星、中子星或黑洞。维恩位移定律 λₘₐₓ T = 常量 与斯特藩–玻尔兹曼定律将恒星表面温度与颜色、光度联系起来，便于恒星分类和距离估算。
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