📚 GCSE WJEC Physics: Last-Minute Revision Notes | GCSE WJEC 物理：考前冲刺笔记
These concise notes cover the essential topics for the WJEC GCSE Physics exams. Use them to quickly review key equations, definitions, and concepts before your test. Focus on understanding the relationships between quantities and how to apply formulas in unfamiliar contexts. The notes are structured around the main units: Electricity, Energy and Waves (Unit 1), and Forces, Space and Radioactivity (Unit 2).
这份紧凑的笔记涵盖了 WJEC 物理会考的核心主题。考前使用它快速回顾关键公式、定义和概念。重点理解物理量之间的关系，并熟练在陌生情境中运用公式。内容围绕主要单元编排：电学、能量与波动（单元一），以及力学、空间与放射性（单元二）。
1. Electric Circuits | 电路基础
Current (I) is the rate of flow of charge, measured in amperes (A). In a series circuit, current is the same at all points. In parallel circuits, the total current is the sum of the currents in each branch.
电流（I）是电荷流动的速率，单位为安培（A）。串联电路中各处电流相等。并联电路中总电流等于各支路电流之和。
Potential difference (V), or voltage, is the energy transferred per unit charge, measured in volts (V). The total voltage across components in series equals the supply voltage. In parallel, each branch receives the full supply voltage.
电势差（V）即电压，是单位电荷转移的能量，单位为伏特（V）。串联元件两端的总电压等于电源电压。并联电路中各支路承受的电压与电源电压相同。
Resistance (R) opposes current. Ohm’s Law: V = IR (at constant temperature). Resistance is measured in ohms (Ω). For a filament lamp, resistance increases with temperature as ions vibrate more.
电阻（R）阻碍电流。欧姆定律：V = IR（温度恒定时）。电阻单位为欧姆（Ω）。对于灯丝灯泡，温度升高时离子振动加剧，电阻增大。
V = I × R
The total resistance in series is R_total = R₁ + R₂ + … In parallel, 1/R_total = 1/R₁ + 1/R₂ + …
串联总电阻：R总 = R₁ + R₂ + … 并联总电阻：1/R总 = 1/R₁ + 1/R₂ + …
Power (P) is the rate of energy transfer, in watts (W). P = IV, P = I²R, P = V²/R. Energy transferred E = Pt = IVt.
功率（P）是能量转移的速率，单位瓦特（W）。P = IV，P = I²R，P = V²/R。转移的能量 E = Pt = IVt。
2. Energy Transfers and Efficiency | 能量转移与效率
Energy is measured in joules (J). The principle of conservation of energy: energy cannot be created or destroyed, only transferred, stored or dissipated.
能量单位为焦耳（J）。能量守恒定律：能量不能被创造或消灭，只能被转移、储存或耗散。
Kinetic energy: E_k = ½mv². Gravitational potential energy: E_p = mgh (where g ≈ 10 N/kg on Earth). Elastic potential energy: E_e = ½kx².
动能：E_k = ½mv²。重力势能：E_p = mgh（地球表面 g ≈ 10 N/kg）。弹性势能：E_e = ½kx²。
E_k = ½mv² E_p = mgh
Work done (W) = force × distance moved in the direction of the force: W = Fd. Work done also transfers energy equal to the force times distance.
做功（W）= 力 × 沿力方向移动的距离：W = Fd。所做的功也等于力与距离的乘积对应的能量转移。
Efficiency = useful output energy transfer ÷ total input energy transfer (×100% for percentage). No device is 100% efficient; some energy is always dissipated as thermal energy.
效率 = 有用输出能量转移 ÷ 总输入能量转移（×100% 为百分比）。没有设备能达到 100% 效率，总有部分能量以热量形式耗散。
3. Domestic Electricity | 家庭用电
Mains electricity in the UK is an alternating current (a.c.) at 230 V, 50 Hz. Alternating current changes direction periodically; direct current (d.c.) flows in one direction only.
英国市电为交流电（a.c.），230 V，50 Hz。交流电周期性改变方向；直流电（d.c.）仅沿一个方向流动。
Live wire (brown) carries the alternating potential difference. Neutral wire (blue) completes the circuit. Earth wire (green/yellow) is a safety feature, providing a low-resistance path to the ground in case of a fault.
火线（棕色）携带交变电势差。零线（蓝色）构成回路。地线（绿/黄色）是安全保护，当发生故障时提供低电阻接地路径。
Fuses and circuit breakers prevent overheating and fires by breaking the circuit if current exceeds a safe level. The fuse rating should be slightly above the normal operating current of the appliance.
保险丝和断路器通过当电流超过安全值时断开电路，防止过热和火灾。保险丝的额定值应略高于用电器正常工作电流。
Power rating of an appliance: P = IV; energy used depends on power and time, shown on electricity bills in kilowatt-hours (kWh). 1 kWh = 3.6 × 10⁶ J.
用电器功率：P = IV；耗能取决于功率和使用时间，电费单以千瓦时（kWh）显示。1 kWh = 3.6 × 10⁶ J。
4. Waves: Properties and Types | 波的性质与类型
Waves transfer energy without transferring matter. In transverse waves, oscillations are perpendicular to the direction of energy transfer (e.g. light, water ripples, all electromagnetic waves). In longitudinal waves, oscillations are parallel to the direction of energy transfer (e.g. sound, seismic P-waves).
波传递能量而不传递物质。横波中，振动方向与能量传递方向垂直（如光、水波、所有电磁波）。纵波中，振动方向与能量传递方向平行（如声波、地震 P 波）。
Key wave measurements: amplitude (maximum displacement from rest), wavelength (λ, distance between two consecutive corresponding points), frequency (f, number of complete waves per second, in hertz Hz). Period T = 1/f.
波的关键测量：振幅（离开平衡位置的最大位移）、波长（λ，相邻两个对应点之间的距离）、频率（f，每秒完整波的数量，单位赫兹 Hz）。周期 T = 1/f。
The wave equation: wave speed v = f λ. Wave speed depends on the medium. For electromagnetic waves in a vacuum, v = c = 3.0 × 10⁸ m/s.
波速方程：波速 v = f λ。波速取决于介质。对于真空中的电磁波，v = c = 3.0 × 10⁸ m/s。
v = f λ T = 1/f
Reflection follows the law: angle of incidence = angle of reflection, measured from the normal. Refraction occurs when waves change speed at a boundary, causing a change in direction unless the wave enters along the normal.
反射定律：入射角等于反射角，均从法线测量。折射发生在波在交界处改变速度时，导致方向改变，除非波沿法线入射。
5. Electromagnetic Spectrum | 电磁波谱
The electromagnetic spectrum, in order of increasing wavelength (or decreasing frequency): gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, radio waves. All travel at the speed of light in a vacuum.
电磁波谱按波长增加（或频率降低）排序：γ 射线、X 射线、紫外线、可见光、红外线、微波、无线电波。所有电磁波在真空中均以光速传播。
Uses: Radio waves – broadcasting, communications; Microwaves – cooking, satellite transmissions; Infrared – thermal imaging, remote controls; Visible light – seeing, optical fibres; Ultraviolet – tanning, fluorescent lamps; X-rays – medical imaging, security; Gamma rays – cancer treatment, sterilisation.
用途：无线电波——广播、通讯；微波——烹饪、卫星传输；红外线——热成像、遥控器；可见光——视觉、光纤；紫外线——皮肤晒黑、荧光灯；X 射线——医疗影像、安检；γ 射线——癌症治疗、灭菌。
Dangers: Ultraviolet can cause skin cancer; X-rays and gamma rays are ionising and can mutate DNA. Higher frequency EM waves carry more energy per photon.
危害：紫外线可致皮肤癌；X 射线和 γ 射线具有电离性，可导致 DNA 突变。频率越高的电磁波，每个光子携带的能量越大。
6. Forces and Motion | 力与运动
A force is a push or pull measured in newtons (N). Contact forces (friction, tension, normal reaction) and non-contact forces (gravity, electrostatic, magnetic).
力是推或拉，单位为牛顿（N）。接触力（摩擦力、张力、法向反作用力）与非接触力（重力、静电力、磁力）。
Scalar quantities have magnitude only (e.g. speed, distance, mass, energy). Vector quantities have both magnitude and direction (e.g. velocity, displacement, force, acceleration).
标量仅有大小（如速率、路程、质量、能量）。矢量既有大小又有方向（如速度、位移、力、加速度）。
Speed (v) = distance ÷ time (m/s). Velocity is speed in a given direction. Acceleration a = change in velocity ÷ time. The gradient of a distance-time graph gives speed; gradient of a velocity-time graph gives acceleration. Area under velocity-time graph gives distance travelled.
速率（v）= 距离 ÷ 时间（m/s）。速度是给定方向上的速率。加速度 a = 速度变化量 ÷ 时间。距离-时间图的斜率代表速率；速度-时间图的斜率代表加速度。速度-时间图下的面积代表走过的距离。
a = (v – u) / t v² = u² + 2as
Newton’s First Law: An object remains at rest or at constant velocity unless acted upon by a resultant force. Newton’s Second Law: F = ma. Newton’s Third Law: For every action force there is an equal and opposite reaction force.
牛顿第一定律：物体若无合力作用，将保持静止或匀速直线运动。牛顿第二定律：F = ma。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。
7. Momentum and Stopping Distances | 动量与制动距离
Momentum p = mv (kg m/s). Momentum is a vector. In a closed system, total momentum before an interaction equals total momentum after (conservation of momentum).
动量 p = mv（kg m/s）。动量是矢量。在一个封闭系统中，相互作用前的总动量等于相互作用后的总动量（动量守恒）。
Force is equal to the rate of change of momentum: F = Δp / Δt. This explains why crumple zones and airbags increase impact time, reducing the force on occupants.
力等于动量变化率：F = Δp / Δt。这解释了为何溃缩区和安全气囊可延长碰撞时间，从而减小对乘员的冲击力。
Stopping distance = thinking distance + braking distance. Thinking distance depends on reaction time (affected by tiredness, alcohol, drugs). Braking distance depends on speed, road conditions, tyre condition, and mass of the vehicle. Braking force does work to reduce kinetic energy to zero.
停止距离 = 反应距离 + 制动距离。反应距离取决于反应时间（受疲劳、酒精、药物影响）。制动距离取决于车速、路面状况、轮胎状况和车辆质量。制动力做功将动能减为零。
8. Radioactivity | 放射性
Radioactive decay is the random process by which unstable atomic nuclei emit radiation to become more stable. Activity is the rate of decay, measured in becquerels (Bq).
放射性衰变是不稳定原子核随机发射辐射以变得更稳定的过程。活度是衰变速率，单位为贝克勒尔（Bq）。
Types of radiation: alpha (α) – helium nucleus (²₄He), highly ionising, stopped by paper, range of a few cm in air; beta (β) – fast electron (⁰₋₁e), moderately ionising, stopped by a few mm of aluminium; gamma (γ) – electromagnetic wave, weakly ionising, stopped by thick lead or concrete.
辐射类型：α 粒子——氦核（²₄He），电离能力强，能被纸阻挡，在空气中传播几厘米；β 粒子——高速电子（⁰₋₁e），电离能力中等，被几毫米铝挡住；γ 射线——电磁波，电离能力弱，需要厚铅或混凝土阻挡。
Nuclear equations must balance total mass number (top) and total atomic number (bottom). In alpha decay, mass number decreases by 4, atomic number by 2. In beta decay, a neutron turns into a proton and an electron; mass number unchanged, atomic number increases by 1.
核方程必须保持质量数（上标）和原子序数（下标）的总量平衡。α 衰变中，质量数减 4，原子序数减 2。β 衰变中，一个中子转变为质子和电子；质量数不变，原子序数加 1。
Half-life is the time taken for the number of radioactive nuclei in a sample to halve. It can be found from a decay graph or calculations. Background radiation comes from rocks, cosmic rays, medical uses, etc.
半衰期是样品中放射性原子核数量减半所需的时间。可通过衰变曲线图或计算求出。本底辐射来自岩石、宇宙射线、医疗应用等。
9. Nuclear Fission and Fusion | 核裂变与核聚变
Nuclear fission is the splitting of a large, unstable nucleus (e.g. uranium-235 or plutonium-239) after absorbing a neutron. It releases a large amount of energy and two or three more neutrons, which can trigger a chain reaction.
核裂变是大型不稳定原子核（如铀-235 或钚-239）吸收一个中子后分裂。释放大量能量和两到三个中子，可引发链式反应。
In a nuclear reactor, control rods (often boron) absorb excess neutrons to control the rate of fission. Moderators (e.g. water, graphite) slow down neutrons so they can be absorbed by further nuclei. The heat generated is used to produce steam that drives turbines to generate electricity.
在核反应堆中，控制棒（通常为硼）吸收多余中子以控制裂变速率。慢化剂（如水、石墨）减慢中子速度，使其能被其他核吸收。产生的热量用来制造蒸汽，驱动涡轮发电。
Nuclear fusion is the joining of two light nuclei (e.g. hydrogen isotopes) to form a heavier nucleus, releasing energy. Fusion happens in stars. It requires extremely high temperature and pressure to overcome electrostatic repulsion. Fusion on Earth is still at the research stage.
核聚变是两个轻原子核（如氢同位素）结合成较重的核，释放能量。聚变发生在恒星内部。它需要极高的温度和压力来克服静电排斥。地球上的受控聚变仍在研究阶段。
10. The Solar System and Universe | 太阳系与宇宙
The Solar System consists of the Sun, eight planets, dwarf planets, moons, asteroids and comets. Planets orbit the Sun in elliptical orbits. Gravity provides the centripetal force keeping objects in stable orbits.
太阳系包括太阳、八大行星、矮行星、卫星、小行星和彗星。行星以椭圆轨道绕太阳运行。引力提供维持稳定轨道所需的向心力。
The Big Bang theory states that the Universe began from an extremely hot, dense point about 13.8 billion years ago and has been expanding ever since. Evidence includes cosmic microwave background radiation (CMBR) and the redshift of light from distant galaxies.
大爆炸理论认为，宇宙起源于约 138 亿年前一个极热、极密的点，并一直在膨胀。证据包括宇宙微波背景辐射（CMBR）和遥远星系的光谱红移。
Redshift: when a galaxy moves away from us, the wavelength of light is stretched, shifting it towards the red end of the spectrum. The greater the redshift, the faster the galaxy is receding. This supports an expanding Universe.
红移：当星系远离我们时，光的波长被拉长，向光谱的红端移动。红移越大，星系退行速度越快。这支持了宇宙正在膨胀的观点。
A stable orbit requires that the gravitational force equals the required centripetal force. For a satellite or planet, orbital speed and radius are related: the closer to the central body, the faster it must move to stay in orbit.
稳定轨道要求引力等于所需的向心力。对于卫星或行星，轨道速度与半径相关：离中心天体越近，需移动得越快才能保持在轨。
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