📚 IGCSE Physics: Last-Minute Revision Notes | IGCSE 物理：考前冲刺笔记
As the IGCSE Physics exam approaches, these concise revision notes cover the essential concepts, key formulas, and common pitfalls across the entire syllabus. Master the core topics and boost your confidence with this last-minute guide.
随着IGCSE物理考试临近，这份简洁的冲刺笔记涵盖了整个大纲的基本概念、关键公式和常见易错点。通过这份考前指南掌握核心主题，增强你的信心。
1. Motion, Forces and Graphs | 运动、力与图像
Scalars have magnitude only (e.g., speed, distance, mass); vectors have both magnitude and direction (e.g., velocity, displacement, force).
标量只有大小（如速率、路程、质量）；矢量既有大小又有方向（如速度、位移、力）。
Average speed = total distance / total time. It is a scalar.
平均速率 = 总路程 / 总时间。它是一个标量。
v = s / t
Acceleration is the rate of change of velocity. a = (v − u) / t, where u is initial velocity, v is final velocity.
加速度是速度的变化率。a = (v − u) / t，其中u为初速度，v为末速度。
For uniform acceleration, use the SUVAT equations (remember they only apply when acceleration is constant).
对于匀加速运动，使用运动学方程（注意它们仅在加速度恒定时适用）。
v = u + a t
s = u t + ½ a t²
v² = u² + 2 a s
On a distance–time graph, the gradient gives speed. On a velocity–time graph, the gradient gives acceleration and the area under the graph gives displacement.
在距离−时间图上，斜率表示速率。在速度−时间图上，斜率表示加速度，图线下的面积表示位移。
Newton’s First Law: An object remains at rest or in uniform motion unless acted upon by a resultant force.
牛顿第一定律：除非受到合外力作用，物体将保持静止或匀速直线运动状态。
Newton’s Second Law: Resultant force = mass × acceleration. F = m a.
牛顿第二定律：合外力 = 质量 × 加速度。F = m a。
Newton’s Third Law: For every action, there is an equal and opposite reaction. These forces act on different objects.
牛顿第三定律：每一个作用力都有一个大小相等、方向相反的反作用力。这两个力作用在不同物体上。
Friction and air resistance oppose motion. Terminal velocity is reached when weight equals air resistance.
摩擦力和空气阻力阻碍运动。当重力等于空气阻力时，物体达到终极速度。
Hooke’s Law: Extension is proportional to force, up to the limit of proportionality. F = k x, where k is the spring constant.
胡克定律：在比例极限内，伸长量与力成正比。F = k x，其中k是弹簧常数。
An object moving in a circle experiences a centripetal force directed towards the centre; its speed is constant but velocity changes.
做圆周运动的物体受到指向圆心的向心力；其速率恒定但速度不断变化。
2. Energy, Work and Power | 能量、功与功率
Energy cannot be created or destroyed, only transferred or stored. The total energy of a closed system remains constant.
能量不能被创造或消灭，只能转移或储存。封闭系统的总能量保持不变。
Kinetic energy (Eₖ) = ½ m v². Gravitational potential energy (Eₚ) = m g h, where g ≈ 9.8 m/s² on Earth.
动能 (Eₖ) = ½ m v²。重力势能 (Eₚ) = m g h，地球上g ≈ 9.8 m/s²。
Work done (W) = force × distance moved in the direction of the force. W = F d. It is measured in joules (J).
功 (W) = 力 × 物体在力的方向上移动的距离。W = F d。单位是焦耳 (J)。
Power is the rate of doing work or transferring energy. P = W / t = E / t. Unit: watt (W).
功率是做功或传递能量的速率。P = W / t = E / t。单位：瓦特 (W)。
Efficiency = (useful energy output / total energy input) × 100%. It can also be expressed in terms of power.
效率 = (有用能量输出 / 总能量输入) × 100%。也可以用功率表示。
Renewable energy resources include solar, wind, hydroelectric, tidal, wave, geothermal and biomass. Non‑renewable resources include fossil fuels and nuclear fuels.
可再生能源包括太阳能、风能、水能、潮汐能、波浪能、地热能和生物质能。不可再生能源包括化石燃料和核燃料。
3. Momentum and Impulse | 动量与冲量
Momentum (p) = mass × velocity. p = m v. It is a vector quantity.
动量 (p) = 质量 × 速度。p = m v。它是一个矢量。
In a closed system, total momentum before a collision equals total momentum after, provided no external resultant force acts (conservation of momentum).
在封闭系统中，如果没有合外力作用，碰撞前的总动量等于碰撞后的总动量（动量守恒）。
Impulse = change in momentum = force × time. F t = m v − m u.
冲量 = 动量的变化 = 力 × 时间。F t = m v − m u。
Car safety features such as seat belts, airbags and crumple zones increase the time over which the collision force acts, reducing the force on the occupants.
汽车安全装置（如安全带、安全气囊和溃缩区）会延长碰撞力的作用时间，从而减小乘员受到的力。
4. Thermal Physics | 热物理
The kinetic particle model explains states of matter: particles in solids vibrate in fixed positions, in liquids they move past each other, and in gases they move rapidly and randomly.
分子运动论解释物态：固体的粒子在固定位置振动，液体的粒子相互滑过，气体的粒子快速无规则运动。
Brownian motion (random movement of small particles suspended in a fluid) provides evidence for the motion of molecules.
布朗运动（悬浮在流体中的微粒做无规则运动）为分子的运动提供了证据。
Internal energy is the sum of the kinetic and potential energies of all particles. Heating increases internal energy; a change of state occurs at constant temperature.
内能是所有粒子的动能和势能的总和。加热增加内能；状态变化在恒温下发生。
Specific heat capacity (c) = energy / (mass × temperature change). Q = m c Δθ. Unit: J/(kg °C).
比热容 (c) = 能量 / (质量 × 温度变化)。Q = m c Δθ。单位：J/(kg °C)。
Specific latent heat (L) = energy / mass for a change of state. Q = m L. Latent heat of fusion (solid ↔ liquid) and vaporisation (liquid ↔ gas).
比潜热 (L) = 状态变化所需的能量 / 质量。Q = m L。熔解潜热（固↔液）和汽化潜热（液↔气）。
Heat transfer methods: conduction (mainly in solids, via particle vibration and free electrons), convection (in fluids, due to density changes) and radiation (infrared waves, no medium required).
热传递方式：传导（主要在固体中，通过粒子振动和自由电子）、对流（在流体中，由于密度变化）和辐射（红外波，无需介质）。
5. Waves | 波
Transverse waves have vibrations perpendicular to the direction of energy transfer (e.g., light, water waves). Longitudinal waves have vibrations parallel to the direction of energy transfer (e.g., sound).
横波的振动方向与能量传递方向垂直（例如光、水波）。纵波的振动方向与能量传递方向平行（例如声波）。
Amplitude is the maximum displacement from the rest position. Wavelength (λ) is the distance between two consecutive crests. Frequency (f) is the number of waves per second.
振幅是离开平衡位置的最大位移。波长 (λ) 是两个相邻波峰间的距离。频率 (f) 是每秒通过的波的数目。
Wave speed: v = f λ. The speed of electromagnetic waves in a vacuum is c = 3.0 × 10⁸ m/s.
波速：v = f λ。电磁波在真空中的速度是 c = 3.0 × 10⁸ m/s。
Reflection: angle of incidence = angle of reflection. Refraction: waves change speed and direction when entering a different medium. Diffraction: waves spread out when passing through a gap or around an obstacle.
反射：入射角等于反射角。折射：波进入不同介质时速度和方向发生改变。衍射：波通过狭缝或遇到障碍物时发生扩散。
The electromagnetic spectrum (in order of increasing frequency): radio, microwave, infrared, visible light, ultraviolet, X‑rays, gamma rays. All travel at c in a vacuum.
电磁波谱（频率递增顺序）：无线电波、微波、红外线、可见光、紫外线、X射线、γ射线。它们在真空中都以光速c传播。
Sound waves are longitudinal and cannot travel through a vacuum. Ultrasound (f > 20 kHz) is used for sonar, medical imaging and cleaning.
声波是纵波，不能在真空中传播。超声波（f > 20 kHz）用于声呐、医学成像和清洗。
6. Light and Optics | 光与光学
Law of reflection: i = r. The image in a plane mirror is virtual, upright, laterally inverted and the same size as the object.
反射定律：入射角等于反射角。平面镜中的像是虚像、正立、左右颠倒且与物体等大。
Refraction is described by Snell’s law: n = sin i / sin r, where n is the refractive index. Light bends towards the normal when entering a denser medium.
折射由斯涅尔定律描述：n = sin i / sin r，其中n是折射率。光进入光密介质时向法线偏折。
Total internal reflection occurs when the angle of incidence exceeds the critical angle (c) and light travels from a denser to a less dense medium. sin c = 1 / n.
当光从光密介质进入光疏介质且入射角大于临界角 (c) 时，发生全内反射。sin c = 1 / n。
Optical fibres use total internal reflection to transmit light signals over long distances.
光纤利用全内反射长距离传输光信号。
Converging (convex) lenses bring parallel rays to a focus. The image formed can be real or virtual depending on object distance. Diverging (concave) lenses always produce virtual, diminished, upright images.
会聚（凸）透镜将平行光会聚到焦点。成像可以是实像或虚像，取决于物距。发散（凹）透镜总是产生虚像、缩小、正立的像。
Magnification = image height / object height. A simple magnifying glass is a convex lens used with the object inside its focal length.
放大率 = 像高 / 物高。简单的放大镜是一块凸透镜，物体放置在焦距之内。
7. Electricity Fundamentals | 电学基础
Electric current (I) is the rate of flow of charge. I = Q / t, unit: ampere (A). Charge is measured in coulombs (C).
电流 (I) 是电荷流动的速率。I = Q / t，单位：安培 (A)。电荷的单位是库仑 (C)。
Potential difference (voltage V) is the energy transferred per unit charge. V = W / Q, unit: volt (V).
电势差（电压V）是单位电荷转移的能量。V = W / Q，单位：伏特 (V)。
Resistance (R) = V / I, unit: ohm (Ω). Ohm’s Law states that V ∝ I at constant temperature for many conductors.
电阻 (R) = V / I，单位：欧姆 (Ω)。欧姆定律指出，在恒温下许多导体的 V ∝ I。
Resistance of a wire depends on length (R ∝ L), cross‑sectional area (R ∝ 1/A) and material (resistivity ρ). R = ρ L / A.
导线的电阻取决于长度（R ∝ L）、横截面积（R ∝ 1/A）和材料（电阻率ρ）。R = ρ L / A。
Resistors in series: Rtotal = R₁ + R₂ + … . Resistors in parallel: 1/Rtotal = 1/R₁ + 1/R₂ + … .
串联电阻：R总 = R₁ + R₂ + … 。并联电阻：1/R总 = 1/R₁ + 1/R₂ + … 。
Electric power: P = I V = I² R = V² / R. Energy transferred: E = P t = I V t. Kilowatt‑hour (kWh) is a unit of energy.
电功率：P = I V = I² R = V² / R。电能转移：E = P t = I V t。千瓦时 (kWh) 是能量单位。
8. Circuit Components and Safety | 电路元件与用电安全
A thermistor has a resistance that decreases as temperature increases. A light‑dependent resistor (LDR) has a resistance that decreases as light intensity increases.
热敏电阻的电阻随温度升高而减小。光敏电阻 (LDR) 的电阻随光照强度增加而减小。
A diode allows current to flow in one direction only. A light‑emitting diode (LED) emits light when forward biased and is much more efficient than filament lamps.
二极管只允许电流沿一个方向流动。发光二极管 (LED) 正向偏置时会发光，效率远高于白炽灯。
A relay uses a small current to switch on a larger current in another circuit, often with an electromagnet.
继电器利用小电流通过电磁铁接通另一个电路中的大电流。
In domestic wiring, the live wire (brown) carries the current at high potential, the neutral wire (blue) completes the circuit, and the earth wire (green/yellow) is a safety path.
在家庭电路中，火线（棕色）承载高电势电流，零线（蓝色）构成回路，地线（黄绿双色）提供安全通路。
Fuses and circuit breakers protect circuits from excessive current. Double insulation (no earth wire) is used for appliances with non‑conductive casings.
保险丝和断路器保护电路免受过电流的损害。双重绝缘（无地线）用于外壳不导电的电器。
9. Magnetism and Electromagnetism | 磁与电磁学
A magnet has a north and south pole; like poles repel, unlike poles attract. The magnetic field lines point from north to south.
磁铁有北极和南极；同名磁极相斥，异名相吸。磁感线从北极指向南极。
An electromagnet is a coil of wire (solenoid) with a soft iron core; its magnetic field can be switched on and off and increased by increasing current or number of turns.
电磁铁是一个带软铁芯的线圈（螺线管）；其磁场可以通断，并可通过增大电流或线圈匝数增强。
The motor effect: a current‑carrying wire in a magnetic field experiences a force. Fleming’s left‑hand rule gives the direction of force (thumb), field (index finger) and current (middle finger).
电动机效应：磁场中的载流导线受到力的作用。弗莱明左手定则：拇指指向力，食指指向磁场，中指指向电流方向。
When a magnet is moved near a coil or a coil moves in a magnetic field, an electromotive force (emf) is induced (electromagnetic induction). This is the generator effect.
当磁铁相对线圈移动或线圈在磁场中运动时，会产生感应电动势（电磁感应）。这就是发电机效应。
Transformers change the size of an alternating voltage. For an ideal transformer: Vp / Vs = Np / Ns and Vp Ip = Vs Is. Step‑up transformers increase voltage, step‑down decrease it.
变压器改变交流电压的大小。理想变压器：Vp / Vs = Np / Ns 且 Vp Ip = Vs Is。
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