📚 IGCSE Edexcel Physics: Last-Minute Revision Notes | IGCSE Edexcel 物理：考前冲刺笔记
This revision guide summarises the essential concepts, equations, and common pitfalls for IGCSE Edexcel Physics. Each section is presented as a quick-fire set of notes to help you consolidate your knowledge right before the exam.
本复习指南总结了IGCSE Edexcel物理的基本概念、方程和常见易错点。每个部分以快速笔记形式呈现，帮助你在考前巩固知识。
1. Motion and Forces | 运动与力
Speed is the rate of change of distance; velocity is speed in a given direction. Acceleration is the rate of change of velocity.
速率是距离的变化率；速度是给定方向上的速率。加速度是速度的变化率。
v = d ÷ t a = (v – u) ÷ t
Newton’s second law states that net force equals mass times acceleration. An object will accelerate only if the resultant force acting on it is not zero.
牛顿第二定律指出，合力等于质量乘以加速度。只有当作用在物体上的合力不为零时，物体才会加速。
F = m × a
For motion in a straight line, you can use the equations of uniformly accelerated motion. Remember to choose the appropriate sign for direction.
对于直线运动，你可以使用匀加速运动方程。记得为方向选择合适的正负号。
v = u + at v² = u² + 2as s = ut + ½at²
Momentum is the product of mass and velocity, and it is conserved in collisions and explosions as long as no external forces act.
动量是质量与速度的乘积，在没有外力作用的情况下，它在碰撞和爆炸中守恒。
p = m × v Total p before = Total p after
Force can also be defined as the rate of change of momentum. A larger force results in a quicker change in momentum.
力也可以定义为动量的变化率。力越大，动量变化越快。
2. Energy, Work and Power | 能量、功和功率
Work done is the energy transferred when a force moves an object through a distance. The unit of work and energy is the joule (J).
功是力使物体移动一段距离时转移的能量。功和能量的单位是焦耳 (J)。
W = F × d (when force and displacement are parallel)
Gravitational potential energy is the energy an object possesses due to its height above the ground. Kinetic energy depends on mass and speed squared.
重力势能是物体因其离地高度而具有的能量。动能取决于质量和速度的平方。
GPE = m × g × h KE = ½ × m × v²
Energy is always conserved; it can be transferred or stored, but never destroyed. In real systems, some energy is dissipated as thermal energy.
能量始终守恒；它可以转移或储存，但绝不会被消灭。在实际系统中，部分能量会以热能形式耗散。
Power is the rate of doing work or the rate of energy transfer. It is measured in watts (W).
功率是做功的快慢或能量转移的速率。它以瓦特 (W) 为单位。
P = W ÷ t P = E ÷ t
Efficiency compares useful output energy to total input energy. No device can be 100% efficient due to unavoidable energy losses.
效率用于比较有用输出能量与总输入能量。由于不可避免的能量损失，任何设备的效率都无法达到100%。
Efficiency = (Useful energy output ÷ Total energy input) × 100%
3. Thermal Physics | 热物理学
Temperature is a measure of the average kinetic energy of particles. Heat is the transfer of thermal energy from a hotter object to a colder one.
温度是粒子平均动能的量度。热量是从较热物体向较冷物体传递的热能。
Conduction is the transfer of heat through a solid by particle vibrations and free electron movement. Metals are good conductors.
热传导是通过粒子振动和自由电子运动在固体中传递热量。金属是良导体。
Convection occurs in fluids (liquids and gases) when warmer, less dense regions rise and cooler, denser regions sink, setting up a convection current.
对流发生在流体（液体和气体）中，较暖、密度较小的区域上升，较冷、密度较大的区域下沉，从而形成对流。
Radiation is the transfer of energy by infrared electromagnetic waves; it does not require a medium and can travel through a vacuum.
辐射是通过红外电磁波传递能量；它不需要介质，可以在真空中传播。
During a change of state (melting, boiling, condensing, freezing), the temperature remains constant even though energy is being transferred. The specific latent heat is the energy required to change the state of 1 kg of a substance without changing its temperature.
在状态变化（熔化、沸腾、冷凝、凝固）期间，即使在转移能量，温度仍保持恒定。比潜热是使1千克物质在温度不变的情况下改变状态所需的能量。
E = m × L
The specific heat capacity is the energy needed to raise the temperature of 1 kg of a substance by 1 °C.
比热容是使1千克物质温度升高1°C所需的能量。
ΔE = m × c × Δθ
4. Waves | 波
Waves transfer energy without transferring matter. In transverse waves, oscillations are perpendicular to the direction of energy travel; in longitudinal waves, oscillations are parallel.
波传递能量而不传递物质。在横波中，振动方向与能量传播方向垂直；在纵波中，振动方向平行。
Amplitude is the maximum displacement from the rest position. Wavelength is the distance between two consecutive points in phase, e.g. crest to crest.
振幅是偏离平衡位置的最大位移。波长是相邻两个同相点之间的距离，例如波峰到波峰。
Frequency is the number of complete waves passing a point per second, measured in hertz (Hz). The wave equation links speed, frequency and wavelength.
频率是每秒通过某点的完整波的数量，以赫兹 (Hz) 为单位。波动方程联系了波速、频率和波长。
v = f × λ
Reflection of waves follows the law of reflection: angle of incidence equals angle of reflection. Refraction occurs when waves change speed as they cross a boundary, causing a change in direction unless they strike along the normal.
波的反射遵循反射定律：入射角等于反射角。折射发生在波穿过边界速度改变时，除非沿法线入射，否则会导致方向改变。
Diffraction is the spreading out of waves when they pass through a gap or around an obstacle. The effect is most noticeable when the gap width is similar to the wavelength.
衍射是波通过狭缝或绕过障碍物时扩散的现象。当缝隙宽度与波长相近时，衍射效果最明显。
5. Light and Sound | 光与声
Light is a transverse electromagnetic wave that travels at approximately 3 × 10⁸ m/s in a vacuum. Sound is a longitudinal mechanical wave requiring a medium; it travels fastest in solids, slower in liquids, and slowest in gases.
光是一种横电磁波，在真空中传播速度约为 3 × 10⁸ m/s。声音是一种需要介质的纵机械波；在固体中传播最快，液体中较慢，气体中最慢。
The law of reflection applies to light. In a plane mirror, the image is virtual, upright, laterally inverted, and the same size as the object.
反射定律适用于光。在平面镜中，像是虚像、正立、横向反转且与物体等大。
Refraction of light is governed by Snell’s law. The refractive index of a medium is the ratio of the speed of light in a vacuum to the speed in the medium.
光的折射遵循斯涅尔定律。介质的折射率是光在真空中的速度与在介质中速度的比值。
n = sin i ÷ sin r n = c ÷ v
Total internal reflection occurs when light travels from a denser to a less dense medium at an angle of incidence greater than the critical angle. The critical angle is given by sin c = 1/n.
当光从光密介质射向光疏介质且入射角大于临界角时，会发生全内反射。临界角由 sin c = 1/n 给出。
Sound waves can be reflected (echoes), refracted, and diffracted. The pitch of a sound depends on frequency; loudness depends on amplitude.
声波可以反射（回声）、折射和衍射。音调取决于频率；响度取决于振幅。
Ultrasound is sound with frequency above 20 kHz. It is used in sonar, medical imaging, and cleaning because of its ability to be partially reflected at boundaries between different tissues or materials.
超声波是频率高于20 kHz的声音。由于它能在不同组织或材料边界发生部分反射，因此应用于声纳、医学成像和清洁。
6. Electricity | 电学
Current is the rate of flow of charge. Conventional current flows from positive to negative, opposite to electron flow.
电流是电荷流动的速率。常规电流方向是从正极到负极，与电子流动方向相反。
I = Q ÷ t
Voltage (potential difference) is the energy transferred per unit charge. Resistance opposes current flow and is measured in ohms (Ω).
电压（电势差）是每单位电荷转移的能量。电阻阻碍电流流动，以欧姆 (Ω) 为单位。
V = W ÷ Q V = I × R
In a series circuit, current is the same everywhere, and the total resistance is the sum of individual resistances. The supply voltage is shared across components.
在串联电路中，各处电流相等，总电阻为各电阻之和。电源电压在各元件间分配。
In a parallel circuit, the voltage across each branch is the same. The total current is the sum of the currents in the branches; the total resistance is less than the smallest individual resistance.
在并联电路中，各支路两端电压相等。总电流等于各支路电流之和；总电阻小于最小的单个电阻。
Electrical power is the rate at which electrical energy is transferred. It can be expressed in terms of current and voltage, or current and resistance.
电功率是电能转移的速率。它可以用电流和电压，或电流和电阻来表示。
P = I × V P = I² × R
Energy transferred by an appliance depends on power and time. The kilowatt-hour (kWh) is a unit of energy commonly used for domestic electricity consumption.
用电器转移的能量取决于功率和时间。千瓦时 (kWh) 是家庭用电常用的能量单位。
E = P × t E = I × V × t
7. Magnetism and Electromagnetism | 磁学和电磁学
Magnets have north and south poles. Like poles repel; unlike poles attract. A magnetic field line shows the direction a north pole would move; it points from north to south.
磁铁有北极和南极。同极相斥；异极相吸。磁力线表示北极移动的方向，从北极指向南极。
An electric current produces a circular magnetic field around a straight wire. Wrapping the wire into a solenoid concentrates the field, creating a strong, uniform field inside, similar to a bar magnet.
电流在直导线周围产生环形磁场。将导线绕成螺线管可集中磁场，内部产生类似条形磁铁的强而均匀的磁场。
Electromagnets are solenoids with an iron core, which greatly increases the magnetic field strength. They can be switched on and off, and are used in relays, electric bells, and lifting magnets.
电磁铁是带有铁芯的螺线管，铁芯大大增强了磁场强度。它们可以开关，用于继电器、电铃和起重磁铁。
The motor effect: a current-carrying conductor in a magnetic field experiences a force. Fleming’s left-hand rule predicts the direction of force (thuMb – Motion, First finger – Field, seCond finger – Current).
电动机效应：磁场中的载流导体会受到力的作用。弗莱明左手定则可以预测力的方向（拇指–运动，食指–磁场，中指–电流）。
F = B × I × L
Electromagnetic induction: when a conductor cuts magnetic field lines, a potential difference (emf) is induced. The effect is increased by moving the conductor faster, using a stronger magnet, or adding more turns to a coil.
电磁感应：当导体切割磁力线时，会感应出电势差（电动势）。通过加快导体运动、使用更强的磁铁或增加线圈匝数可以增强该效应。
Transformers change the size of an alternating voltage. A step-up transformer increases voltage and decreases current; a step-down transformer does the opposite.
变压器可以改变交流电压的大小。升压变压器升高电压、降低电流；降压变压器则相反。
Vₚ ÷ Vₛ = Nₚ ÷ Nₛ Vₚ × Iₚ = Vₛ × Iₛ (ideal)
8. Atomic Physics and Radioactivity | 原子物理与放射性
Atoms consist of a small, dense nucleus containing protons and neutrons, surrounded by electrons in energy levels. The nucleus is held together by the strong nuclear force.
原子由包含质子和中子的致密小原子核以及处于能级中的电子组成。原子核由强核力束缚在一起。
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Their chemical properties are identical, but some isotopes are radioactive.
同位素是质子数相同但中子数不同的同种元素的原子。它们的化学性质相同，但有些同位素具有放射性。
Radioactive decay is a random process where unstable nuclei emit alpha, beta, or gamma radiation. Alpha particles are helium nuclei, beta particles are fast electrons, and gamma rays are electromagnetic waves.
放射性衰变是一个随机过程，不稳定的原子核会发射α、β或γ辐射。α粒子是氦核，β粒子是快速电子，γ射线是电磁波。
Activity is the number of decays per second, measured in becquerels (Bq). Half-life is the average time taken for the activity of a radioactive source to halve.
活度是每秒衰变次数，以贝克勒尔 (Bq) 为单位。半衰期是放射源活度减半所需的平均时间。
Background radiation comes from natural sources such as radon gas, cosmic rays, and rocks, as well as artificial sources. The dose received is measured in sieverts (Sv).
背景辐射来自天然源，如氡气、宇宙射线和岩石，以及人造源。接收的剂量以希沃特 (Sv) 为单位。
Uses of radiation include sterilising equipment (gamma), smoke detectors (alpha), thickness gauging (beta), and medical tracers (gamma or beta with short half-lives). Safety precautions include distance, shielding, and limiting exposure time.
辐射的用途包括设备消毒（γ）、烟雾探测器（α）、厚度测量（β）和医学示踪剂（短半衰期的γ或β）。安全措施包括保持距离、屏蔽和限制暴露时间。
Nuclear fission is the splitting of a large nucleus (e.g., uranium-235) after absorbing a neutron, releasing energy and more neutrons. Nuclear fusion is the joining of light nuclei (e.g., hydrogen) to form a heavier nucleus, releasing even more energy.
核裂变是大原子核（如铀-235）吸收中子后分裂，释放能量和更多中子。核聚变是轻核（如氢）结合形成更重的原子核，释放更多能量。
9. Space Physics | 太空物理学
The Solar System consists of the Sun, eight planets, their moons, and smaller bodies such as asteroids and comets. Planets orbit the Sun in elliptical paths.
太阳系由太阳、八大行星、它们的卫星以及小行星和彗星等较小天体组成。行星以椭圆轨道绕太阳运行。
Gravitational force provides the centripetal force that keeps planets and satellites in orbit. The orbital speed of a planet decreases with increasing distance from the Sun.
引力提供维持行星和卫星沿轨道运行的向心力。行星的轨道速度随与太阳距离的增加而减小。
v = 2πr ÷ T
A galaxy is a vast collection of billions of stars, gas, and dust. The Milky Way is our galaxy. The Universe contains billions of galaxies, and it began with the Big Bang about 13.8 billion years ago.
星系是由数十亿颗恒星、气体和尘埃组成的庞大集合。银河系是我们的星系。宇宙包含数十亿个星系，它始于约138亿年前的大爆炸。
Evidence for the Big Bang includes the redshift of light from distant galaxies, showing they are moving away, and the cosmic microwave background radiation. The greater the redshift, the faster a galaxy is receding.
大爆炸的证据包括来自遥远星系的光发生红移，表明它们正在远离，以及宇宙微波背景辐射。红移越大，星系远离的速度越快。
10. Key Equations and Final Tips | 关键方程与最后提示
Memorise the main equations, but also understand how to rearrange them. The table below summarises the most frequently examined relationships.
记住主要方程，但也要理解如何移项。下表总结了最常考查的关系。
| Quantity | Equation | Units |
|---|---|---|
| Speed | v = d ÷ t | m/s |
| Acceleration | a = (v – u) ÷ t | m/s² |
| Force | F = m × a | N |
| Momentum | p = m × v | kg m/s |
| Kinetic Energy | KE = ½ m v² | J |
| Work Done | W = F × d | J |
| Power | P = E ÷ t | W |
| Electrical Power | P = I × V | W |
| Ohm’s Law | V = I × R | V, A, Ω |
| Wave Speed | v = f × λ | m/s |
| Transformer | Vₚ / Vₛ = Nₚ / Nₛ | – |
Always show your working, include units, and check the number of significant figures. For calculation questions, begin by writing the formula, then substitute values before calculating the answer.
始终展示解题步骤，注明单位，并检查有效数字。对于计算题，先写出公式，然后代入数值再算出答案。
In practical-based questions, be ready to describe how to reduce errors (e.g., repeating measurements, using fiducial markers, checking zero errors).
在实验类题目中，准备好描述如何减少误差（例如，重复测量、使用基准标记、检查零误差）。
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