Year 12 CCEA Physics: Core Concepts Summary | Year 12 CCEA 物理：核心知识点梳理

📚 Year 12 CCEA Physics: Core Concepts Summary | Year 12 CCEA 物理：核心知识点梳理

This revision guide summarises the essential topics covered in Year 12 of the CCEA GCE Physics specification. The core content spans mechanics, electricity, waves, photons and astronomy, together with the practical skills needed for the AS 3 assessment. Mastering these concepts will build a solid foundation for the A2 course and examinations.

本复习指南概括了CCEA GCE物理课程Year 12阶段的核心内容，涵盖力学、电学、波动、光子和天文学，以及AS 3评估所需的实验技能。掌握这些知识将为A2课程和考试奠定坚实基础。

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1. Scalars and Vectors | 标量与矢量

Physical quantities can be classified as scalars (magnitude only) or vectors (magnitude and direction). Examples of scalars include distance, speed, mass, energy and time. Vectors include displacement, velocity, acceleration, force and momentum.

物理量可分为标量（只有大小）和矢量（既有大小又有方向）。标量如路程、速率、质量、能量和时间；矢量如位移、速度、加速度、力和动量。

When adding vectors, we must take direction into account. For perpendicular vectors, use Pythagoras’ theorem and trigonometry to find the resultant. Resolving a vector into perpendicular components is a key skill for analysing forces on inclined planes.

矢量相加必须考虑方向。对于互相垂直的矢量，用勾股定理和三角函数求合矢量。将矢量分解成垂直分量是分析斜面受力情况的关键技能。

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2. Equations of Motion | 运动学方程

For uniform acceleration, the five suvat equations relate displacement s, initial velocity u, final velocity v, acceleration a, and time t. These equations are derived from definitions and only apply when acceleration is constant.

对于匀加速运动，五个SUVAT方程将位移s、初速度u、末速度v、加速度a和时间t联系起来。这些方程由定义推导而来，仅适用于加速度恒定的情况。

v = u + at

s = ut + ½at²

v² = u² + 2as

s = ½(u + v)t

Free fall near Earth’s surface is a special case with a = g ≈ 9.81 m s¯² directed downwards. Graphically, velocity–time, displacement–time and acceleration–time graphs provide visual interpretation of motion.

地球表面附近的自由落体是一种特殊情况，加速度 a = g ≈ 9.81 m s¯²，方向向下。通过速度–时间、位移–时间和加速度–时间图像可以直观地解释运动。

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3. Newton’s Laws and Linear Momentum | 牛顿定律与动量

Newton’s first law: an object remains at rest or in uniform motion unless acted upon by a resultant force. Second law: F = ma, where F is the resultant force, m is mass and a is acceleration. Third law: if body A exerts a force on body B, body B exerts an equal and opposite force on body A.

牛顿第一定律：物体保持静止或匀速直线运动状态，除非受到合力作用。第二定律：F = ma，其中F为合力，m为质量，a为加速度。第三定律：若物体A对物体B施加力，则B对A施加大小相等、方向相反的力。

Linear momentum p = mv is a vector. In any interaction, total momentum is conserved provided no external resultant force acts. The impulse of a force equals the change in momentum: FΔt = Δp. This explains how airbags and crumple zones reduce impact force by extending the time over which momentum changes.

线动量 p = mv 是矢量。在无外力合力作用的情况下，任何相互作用中总动量守恒。力的冲量等于动量的变化：FΔt = Δp。这解释了安全气囊和溃缩区如何通过延长动量变化的时间来减小冲击力。

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4. Work, Energy and Power | 功、能和功率

Work done W = F s cosθ, where θ is the angle between force and displacement. Kinetic energy Eₛ = ½mv²; gravitational potential energy Eₙ = mgh. The principle of conservation of energy states that energy cannot be created or destroyed, only transferred.

做功 W = F s cosθ，θ为力与位移的夹角。动能 Eₛ = ½mv²；重力势能 Eₙ = mgh。能量守恒原理指出能量不能凭空产生或消失，只能转化和转移。

Power is the rate of doing work or transferring energy: P = W/t. For a constant force moving at speed v, P = Fv. Efficiency = useful output energy / total input energy × 100%.

功率是做功或能量转移的速率：P = W/t。对于恒力以速度v运动的情形，P = Fv。效率 = 有用输出能量 / 总输入能量 × 100%。

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5. Stress, Strain and Young Modulus | 应力、应变与杨氏模量

For solids, stress σ = F/A (force per unit area) and strain ε = ΔL/L (extension per unit length). Hooke’s law states that extension is proportional to force up to the limit of proportionality, with F = kΔx. The Young modulus E = stress/strain = (F/A) / (ΔL/L). It is a material property indicating stiffness.

对于固体，应力 σ = F/A（单位面积受力），应变 ε = ΔL/L（单位长度的伸长量）。胡克定律指出在比例极限内，伸长量与力成正比，F = kΔx。杨氏模量 E = 应力/应变 = (F/A) / (ΔL/L)，它是表征材料刚度的属性。

Beyond the elastic limit, permanent (plastic) deformation occurs. Stress–strain graphs distinguish brittle, ductile and polymeric materials. The area under a force–extension graph gives the work done in stretching the sample.

超过弹性极限后，产生永久（塑性）变形。应力–应变图可区分脆性、韧性和高分子材料。力–伸长图下的面积表示拉伸样品所做的功。

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6. Electric Current, Resistance and Circuits | 电流、电阻与电路

Electric current I = ΔQ/Δt, measured in amperes. Potential difference V = W/Q. Resistance R = V/I. Ohm’s law states that for an ohmic conductor at constant temperature, V ∝ I. Resistivity ρ is a material property: R = ρL/A, where L is length and A is cross-sectional area.

电流 I = ΔQ/Δt，单位安培。电势差 V = W/Q。电阻 R = V/I。欧姆定律指出，对于温度恒定的欧姆导体，V ∝ I。电阻率 ρ 是材料属性：R = ρL/A，L为长度，A为截面积。

Property	Series	Parallel
Current	I = I&sub1; = I&sub2;	I = I&sub1; + I&sub2;
p.d.	V = V&sub1; + V&sub2;	V = V&sub1; = V&sub2;
Resistance	Rₛ = R&sub1; + R&sub2;	1/Rₛ = 1/R&sub1; + 1/R&sub2;

Using Kirchhoff’s laws, we can analyse any DC network. Kirchhoff’s first law (junction rule): the sum of currents entering a junction equals the sum leaving. Second law (loop rule): in a closed loop, the sum of e.m.f.s equals the sum of p.d.s.

利用基尔霍夫定律可分析任何直流电路网络。基尔霍夫第一定律（节点规则）：流入节点的电流之和等于流出电流之和。第二定律（回路规则）：闭合回路中，电动势之和等于各电势差之和。

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7. Potential Dividers and Internal Resistance | 电位分压与内阻

A potential divider uses two resistors in series to produce a fraction of the input voltage. The output voltage across R&sub2; is V_out = V_in × (R&sub2;/(R&sub1;+R&sub

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