📚 IGCSE AQA Physics: Last-Minute Revision Notes | IGCSE AQA 物理：考前冲刺笔记
These last-minute revision notes cover the core concepts and equations for the IGCSE AQA Physics specification, helping you review quickly and effectively before the exam. Focus on key definitions, formulas, and common pitfalls.
这份考前冲刺笔记涵盖了 IGCSE AQA 物理大纲的核心概念和方程，帮助你快速高效地复习。关注关键定义、公式和常见易错点。
1. Energy Stores and Transfers | 能量储存与转移
Energy can be stored in various forms: kinetic, gravitational potential, elastic potential, thermal, chemical, nuclear, magnetic, and electrostatic. It is transferred mechanically (by forces), electrically, by heating, or by radiation.
能量可以以多种形式储存：动能、重力势能、弹性势能、热能、化学能、核能、磁能和静电。能量的转移方式包括机械做功（力）、电功、加热和辐射。
The principle of conservation of energy states that energy cannot be created or destroyed, only transferred between stores. In any closed system, total energy is constant.
能量守恒定律指出，能量不能被创造或消灭，只能在不同的储存之间转移。在任何封闭系统中，总能量保持不变。
Eₖ = ½ m v² | ΔEₚ = m g Δh | E = P t
Kinetic energy (Eₖ) depends on mass and speed squared; gravitational potential energy (ΔEₚ) depends on mass, gravitational field strength g and height change. Power P is the rate of energy transfer: 1 W = 1 J/s.
动能取决于质量和速度的平方；重力势能的变化取决于质量、重力场强度 g 和高度变化。功率 P 是能量转移的速率：1 瓦 = 1 焦/秒。
Efficiency = useful output energy transfer / total input energy transfer (or useful power output / total power input). It can be expressed as a decimal or percentage. Sankey diagrams show energy transfers; the width of each arrow is proportional to the amount of energy.
效率 = 有用输出能量转移 / 总输入能量转移（或有用功率输出 / 总功率输入）。可用小数或百分比表示。桑基能量流动图显示能量转移，箭头宽度与能量数量成正比。
2. Electricity: Circuits and Components | 电路与元件
Current I is the rate of flow of charge: I = Q / t. In a series circuit, current is the same everywhere; in parallel, the total current from the source is the sum of the branch currents. Potential difference (voltage) V = energy transferred per unit charge.
电流 I 是电荷流动的速率：I = Q / t。在串联电路中，各处电流相等；在并联电路中，总电流是各支路电流之和。电势差（电压）V = 单位电荷转移的能量。
V = I R | P = I V = I²R
Ohm’s law states that V = I R for a fixed resistor at constant temperature. Resistance R depends on the material, length (R ∝ L) and cross-sectional area (R ∝ 1/A). Power dissipated is P = I V.
欧姆定律指出，对于定值电阻在恒温下，V = I R。电阻取决于材料、长度（R ∝ L）和横截面积（R ∝ 1/A）。电功率 P = I V。
Series: R_total = R₁ + R₂ + …; the total resistance is greater than each individual. Parallel: 1/R_total = 1/R₁ + 1/R₂ + …; total resistance is less than the smallest individual resistor. Components like diodes only allow current in one direction; thermistors (resistance decreases with temperature rise) and LDRs (resistance decreases with light intensity) are common in sensor circuits.
串联：总电阻 R = R₁ + R₂ + … 大于任一单个电阻。并联：1/R = 1/R₁ + 1/R₂ + … 总电阻小于最小的单个电阻。二极管等元件只允许单向导电；热敏电阻（温度升高电阻下降）和光敏电阻（光照增强电阻下降）常用于传感器电路。
3. Particle Model of Matter | 物质粒子模型
Density ρ = mass / volume, unit kg/m³. To measure density, find mass using a balance, and volume by measuring dimensions (regular solid) or displacement (irregular solid). Gases have very low densities compared to solids and liquids.
密度 ρ = 质量 / 体积，单位 kg/m³。测量密度时，用天平测质量，规则固体用尺寸计算体积，不规则固体用排水法测体积。气体密度远低于固体和液体。
Internal energy is the total kinetic and potential energy of particles. Heating increases the internal energy. The temperature rise Δθ depends on mass, specific heat capacity c, and energy supplied: ΔE = m c Δθ.
内能是粒子动能和势能的总和。加热会增加内能。温度上升 Δθ 取决于质量、比热容 c 和提供的能量：ΔE = m c Δθ。
ΔE = m c Δθ | ΔE = m L
During a change of state (melting, boiling) the temperature stays constant even though energy is still being supplied. Specific latent heat L is the energy required to change the state of 1 kg of a substance without a temperature change: L_f for fusion, L_v for vaporisation.
在状态改变（熔化、沸腾）过程中，即使持续供热，温度也保持不变。比潜热 L 是 1 kg 物质在温度不变时改变物态所需的能量：熔化用熔化潜热 L_f，汽化用汽化潜热 L_v。
Gas pressure is caused by particles colliding with container walls. Increasing temperature (at constant volume) increases pressure because particles move faster and hit walls harder and more often. Boyle’s law for a fixed mass of gas at constant temperature: p V = constant, so p₁V₁ = p₂V₂.
气体压强由粒子撞击容器壁产生。体积不变时，升温会增大压强，因为粒子运动加快，撞击更频繁更有力。玻意耳定律：定质量定温气体，压强与体积成反比，p V = 常数，即 p₁V₁ = p₂V₂。
4. Atomic Structure and Radioactivity | 原子结构与放射性
Atoms consist of a nucleus containing protons (+ charge) and neutrons (neutral), with electrons (−) orbiting in shells. Atomic number Z = number of protons; mass number A = protons + neutrons. Isotopes have same Z but different A.
原子由带正电质子和不带电中子组成的原子核，以及核外分层排布的电子组成。原子序数 Z = 质子数；质量数 A = 质子数 + 中子数。同位素质子数相同但中子数不同。
Some nuclei are unstable and decay, emitting radiation: alpha (α) particles – helium nucleus (2p+2n), strongly ionising, stopped by paper; beta (β) – fast electron, moderately ionising, stopped by aluminium; gamma (γ) – electromagnetic wave, weakly ionising, very penetrating, reduced by lead or thick concrete.
一些原子核不稳定，会衰变并放出射线：α 粒子是氦原子核，电离能力最强，被纸挡住；β 粒子是高速电子，电离能力中等，被铝片挡住；γ 射线是电磁波，电离能力最弱，穿透力最强，可用铅或厚混凝土减弱。
Nuclear equations must balance: total mass numbers and total atomic numbers are equal on both sides. Activity is the number of decays per second, measured in becquerels (Bq). Half-life is the time taken for half of the nuclei in a sample to decay or for the activity to halve.
核反应方程必须配平：总质量数和总原子序数在反应前后守恒。活度是每秒衰变次数，单位贝可勒尔 (Bq)。半衰期是半数原子核发生衰变所需的时间，或活度减半的时间。
Radioactive sources are used in medicine (tracers, radiotherapy) and industry (thickness gauges, smoke alarms). Safety precautions: use tongs, point away from body, keep exposure time short, store in lead-lined boxes.
放射源用于医学（示踪、放疗）和工业（测厚仪、烟雾报警器）。安全措施：使用镊子，避免指向人体，缩短暴露时间，存放在铅衬容器中。
5. Forces and Motion | 力与运动
Scalars have magnitude only (speed, distance, mass, energy); vectors have magnitude and direction (velocity, displacement, force, acceleration). Motion can be analysed using speed = distance / time for constant speed, or using the SUVAT equations for uniform acceleration.
标量只有大小（速率、路程、质量、能量）；矢量既有大小又有方向（速度、位移、力、加速度）。匀速运动可用速度 = 路程/时间，匀加速直线运动可用运动学公式分析。
v = u + a t | s = u t + ½ a t² | v² = u² + 2 a s
where u = initial velocity, v = final velocity, a = acceleration, t = time, s = displacement. Acceleration due to gravity g = 9.8 m/s² near Earth’s surface.
式中 u 初速度，v 末速度，a 加速度，t 时间，s 位移。近地面重力加速度 g = 9.8 m/s²。
Newton’s First Law: an object remains at rest or in uniform motion unless acted on by a resultant force. Second Law: F = m a, the resultant force is proportional to mass and acceleration. Third Law: when two objects interact, forces are equal and opposite.
牛顿第一定律：物体在不受合力作用时保持静止或匀速直线运动。第二定律：F = m a，合力与质量、加速度成正比。第三定律：两物体相互作用时，作用力与反作用力大小相等、方向相反。
Stopping distance = thinking distance (depends on driver’s reaction time, speed) + braking distance (depends on speed, mass, road and tyre conditions, brake condition). Braking force causes deceleration, doing work to reduce kinetic energy.
停车距离 = 反应距离（取决于驾驶员反应时间、车速） + 制动距离（取决于速度、质量、路面及轮胎状况、制动性能）。制动力做功减少动能，使车减速。
Momentum p = m v, conserved in a closed system. Change in momentum = impulse = F Δt. This explains why crumple zones and airbags reduce injury by extending collision time and therefore reducing the peak force.
动量 p = m v，在封闭系统中守恒。动量变化等于冲量 F Δt。这解释了为何溃缩区和安全气囊通过延长碰撞时间减小峰值力，从而减少伤害。
6. Waves and the Electromagnetic Spectrum | 波与电磁波谱
Waves transfer energy without transferring matter. Transverse waves: oscillations perpendicular to energy transfer (e.g., light, water waves, all EM waves). Longitudinal waves: oscillations parallel to energy transfer (e.g., sound).
波传递能量而不传递物质。横波：振动方向垂直于能量传递方向（如光、水波、所有电磁波）。纵波：振动方向平行于能量传递方向（如声波）。
v = f λ
Wave speed v = frequency f × wavelength λ. Frequency measured in hertz (Hz), wavelength in metres (m). The period T = 1/f.
波速 v = 频率 f × 波长 λ。频率单位赫兹 (Hz)，波长单位米 (m)。周期 T = 1/f。
Reflection obeys law: angle of incidence = angle of reflection. Refraction occurs at boundaries: when a wave enters a denser medium it slows down and bends towards the normal. Dispersion splits white light into a spectrum due to different wavelengths refracting by different amounts.
反射遵循定律：入射角 = 反射角。折射发生在界面处：波进入光密介质时速度变慢，折向法线。色散将白光分解为光谱，因为不同波长折射程度不同。
The electromagnetic spectrum in order of decreasing wavelength / increasing frequency: radio, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. All travel at the speed of light in vacuum (3.0 × 10⁸ m/s). Uses: radio for communication, microwaves for satellite TV and cooking, infrared for thermal imaging, visible for seeing, UV for sterilization, X-rays for medical imaging, gamma for cancer treatment.
电磁波谱按波长减小/频率增大排序：无线电波、微波、红外线、可见光、紫外线、X 射线、γ 射线。真空中速度均为 3.0×10⁸ m/s。用途：无线电通信、微波用于卫星电视和烹饪、红外热成像、可见光观察、紫外线杀菌、X 射线医学成像、γ 射线治癌。
7. Magnetism and Electromagnetism | 磁学和电磁学
Permanent magnets produce their own magnetic field. Like poles repel, unlike poles attract. A magnetic field can be represented by field lines that run from north to south. The Earth’s core is magnetic, giving a field that points roughly geographically north-south; the north pole of a compass points to Earth’s magnetic south pole (near geographic north).
永磁体产生自身的磁场。同性相斥，异性相吸。磁场可用从 N 指向 S 的磁感线表示。地核有磁性，产生大致南北向的磁场；指南针北极指向地球的磁南极（近地理北极）。
When a current flows through a wire, a circular magnetic field is produced around it. A solenoid concentrates the field, creating a uniform field inside – an electromagnet whose strength can be increased by adding an iron core, increasing current, or adding more turns.
电流通过导线时，周围产生环形磁场。螺线管集中磁场，内部形成匀强磁场——即电磁铁，加铁芯、增大电流或增加匝数可增强磁场。
The motor effect: a current-carrying conductor placed in a magnetic field experiences a force. The direction of force is given by Fleming’s left-hand rule: thumb = force (motion), first finger = field (N to S), second finger = current (+ to -). Force F = B I L (perpendicular field, current and length). This principle is used in electric motors and loudspeakers.
电动机效应：通电导体在磁场中受到力的作用。力的方向用弗莱明左手定则判断：拇指 = 力（运动），食指 = 磁场（N 到 S），中指 = 电流（+ 到 -）。力大小 F = B I L（磁场、电流、长度互相垂直时）。此原理用于电动机和扬声器。
The generator effect: when a conductor moves through a magnetic field (or a field changes around a conductor), an emf is induced across its ends. If the conductor is part of a complete circuit, a current flows. Direction is given by Fleming’s right-hand rule. This is electromagnetic induction, used in alternators and dynamos to generate electricity.
发电机效应：导体在磁场中运动（或导体周围的磁场变化）时，两端产生感应电动势。若形成闭合回路，则产生感应电流。方向用右手定则判断。电磁感应原理用于交流发电机和直流发电机。
Transformers change the size of an alternating voltage. An alternating current in the primary coil produces a changing magnetic field, which induces an alternating voltage in the secondary coil. For an ideal transformer: Vₛ / Vₚ = Nₛ / Nₚ (voltage ratio = turns ratio). Transformers only work with AC.
变压器改变交流电压的大小。原线圈的交流电产生变化的磁场，在副线圈中感应出交流电压。理想变压器：Vₛ / Vₚ = Nₛ / Nₚ （电压比 = 匝数比）。变压器只能用于交流电。
8. Space Physics | 空间物理
Our Solar System consists of the Sun, eight planets, dwarf planets, moons, asteroids and comets. Planets orbit the Sun in near-circular ellipses. Gravity provides the centripetal force for orbits.
太阳系由太阳、八颗行星、矮行星、卫星、小行星和彗星组成。行星以近乎圆形的椭圆轨道绕太阳运行。引力提供轨道运动所需的向心力。
A star is formed from a cloud of dust and gas (nebula) pulled together by gravity. As the core becomes hot and dense, nuclear fusion of hydrogen into helium begins, releasing vast energy. Stable stars like the Sun balance radiation pressure outward against gravity inward.
恒星由星云在引力作用下收缩形成。核心变热变密后，氢聚变为氦的核反应开始，释放巨大能量。像太阳这样的稳定恒星，向外的辐射压与向内的引力平衡。
The life cycle of a star depends on its mass. A star similar in mass to the Sun becomes a red giant, then sheds outer layers as a planetary nebula, leaving a white dwarf. A star much more massive than the Sun becomes a red supergiant, then explodes as a supernova, leaving either a neutron star or a black hole.
恒星的演化路径取决于其质量。类似太阳质量的恒星变成红巨星，然后外层抛射为行星状星云，中心留下白矮星。远大于太阳的恒星演化为红超巨星，接着发生超新星爆炸，留下中子星或黑洞。
The redshift observed in light from distant galaxies shows that they are moving away from us. The further away the galaxy, the greater the redshift, indicating the Universe is expanding. This supports the Big Bang theory, which states that the Universe began from an extremely hot, dense point about 13.8 billion years ago. Cosmic microwave background radiation (CMBR) is remnant energy from the early Universe, further supporting the Big Bang.
来自遥远星系的光谱出现红移，表明它们正在远离我们。星系越远，红移越大，这说明宇宙正在膨胀。这支持了大爆炸理论：宇宙约 138 亿年前始于一个极热极密的点。宇宙微波背景辐射 (CMBR) 是早期宇宙的残余能量，也支持大爆炸理论。
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