📚 IGCSE OCR Physics: Last-Minute Revision Notes | IGCSE OCR 物理：考前冲刺笔记
These concise revision notes cover the essential topics for IGCSE OCR Physics, designed to help you quickly recall key definitions, formulas, and concepts before the exam. Each section pairs an English explanation with a Chinese version, so you can reinforce your understanding in both languages.
这份精炼的考前冲刺笔记涵盖 IGCSE OCR 物理的核心内容，旨在帮助你快速回顾重要定义、公式和概念。每个小节都采用英中对照的方式，方便你在两种语言中巩固理解。
1. Motion | 运动
Speed is the distance travelled per unit time. It is a scalar quantity, meaning it has magnitude only.
速率是单位时间内经过的距离，是标量，只有大小没有方向。
Velocity is speed in a given direction. It is a vector quantity, so both magnitude and direction matter.
速度是给定方向上的速率，是矢量，因此大小和方向都很重要。
Acceleration is the rate of change of velocity: a = (v – u) / t, where u is initial velocity, v is final velocity, and t is the time taken.
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，t 为所用时间。
v = u + at s = ut + ½at² v² = u² + 2as
The gradient of a distance-time graph gives speed. The gradient of a velocity-time graph gives acceleration, and the area under the graph gives displacement.
距离-时间图的斜率表示速率；速度-时间图的斜率表示加速度，图线下的面积表示位移。
2. Forces | 力
A force can change an object’s shape, speed, or direction. Forces are vectors measured in newtons (N).
力可以改变物体的形状、速率或运动方向。力是矢量，单位为牛顿 (N)。
Newton’s second law: F = ma, where F is the resultant force, m is mass, and a is acceleration.
牛顿第二定律：F = ma，其中 F 为合力，m 为质量，a 为加速度。
Mass is the amount of matter in an object (kg), while weight is the force due to gravity (N), given by W = mg on Earth g ≈ 9.8 m/s².
质量是物体所含物质的多少 (kg)，而重力是地球引力产生的力 (N)，由 W = mg 计算，地表 g ≈ 9.8 m/s²。
Inertia is the tendency of an object to resist changes in its motion. Stopping distance = thinking distance + braking distance.
惯性是物体抵抗运动状态变化的趋势。停车距离 = 反应距离 + 制动距离。
Momentum p = mv. In a closed system, total momentum before a collision equals total momentum after (conservation of momentum).
动量 p = mv。在封闭系统中，碰撞前的总动量等于碰撞后的总动量（动量守恒）。
3. Energy | 能量
Energy is measured in joules (J). Forms include kinetic, gravitational potential, elastic, thermal, chemical, nuclear, and more.
能量的单位是焦耳 (J)，形式包括动能、重力势能、弹性势能、热能、化学能、核能等。
KE = ½mv² GPE = mgh
Work done W = Fd, where F is force and d is distance moved in the direction of the force. Power P = W/t or P = E/t (watts, W).
做功 W = Fd，F 为力，d 为沿力方向移动的距离。功率 P = W/t 或 P = E/t，单位为瓦特 (W)。
Efficiency = useful output energy ÷ total input energy × 100%. No device can be more than 100% efficient due to energy dissipated as heat.
效率 = 有用输出能量 ÷ 总输入能量 × 100%。由于能量会以热的形式耗散，任何设备的效率都不可能超过 100%。
Energy cannot be created or destroyed, only transferred, stored, or dissipated. This is the principle of conservation of energy.
能量不能被创造或消灭，只能被转移、储存或耗散。这就是能量守恒定律。
4. Waves | 波
Waves transfer energy without transferring matter. Transverse waves (e.g., light, water ripples) oscillate perpendicular to the direction of energy transfer; longitudinal waves (e.g., sound) oscillate parallel to it.
波传递能量而不传递物质。横波（如光、水波）的振动方向与能量传播方向垂直；纵波（如声波）的振动方向与传播方向平行。
v = fλ
Here v is wave speed (m/s), f is frequency (Hz), and λ (lambda) is wavelength (m). The period T = 1/f.
式中 v 为波速 (m/s)，f 为频率 (Hz)，λ 为波长 (m)。周期 T = 1/f。
The electromagnetic spectrum, in order of decreasing wavelength: radio, microwave, infrared, visible light, ultraviolet, X-ray, gamma ray. All travel at 3.0×10&sup8; m/s in a vacuum.
电磁波谱按波长递减排列：无线电波、微波、红外线、可见光、紫外线、X 射线、伽马射线。所有电磁波在真空中的传播速度均为 3.0×10&sup8; m/s。
Reflection, refraction, and diffraction are wave behaviours. Refraction occurs when waves change speed at a boundary, causing a change in direction unless they strike the boundary along the normal.
反射、折射和衍射属于波动现象。波在界面处改变速度时会发生折射，除非波沿着法线入射，否则传播方向会改变。
5. Electricity | 电学
Current I is the rate of flow of charge, measured in amperes (A). Charge Q = I t, measured in coulombs (C).
电流 I 是电荷流动的速率，单位安培 (A)。电荷 Q = I t，单位库仑 (C)。
V = IR P = IV E = Pt
V is potential difference (volts, V), R is resistance (ohms, Ω). Power P (W) = I V. Energy E (J) = P t.
V 为电势差（伏特，V），R 为电阻（欧姆，Ω）。功率 P (W) = I V，能量 E (J) = P t。
In series circuits: current is the same everywhere; total resistance Rtotal = R1 + R2 + … ; the sum of p.d.s equals the supply p.d.
串联电路中各处电流相等；总电阻 R总 = R1 + R2 + …；各用电器两端电压之和等于电源电压。
In parallel circuits: p.d. is the same across each branch; total current is the sum of branch currents; total resistance is less than the smallest individual resistance.
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支路电阻。
| Component | Graph characteristic |
|---|---|
| Fixed resistor | Straight line through origin (ohmic) |
| Filament lamp | Curve, as resistance increases with temperature |
| Diode | Forward bias: current flows above threshold; reverse bias: near zero |
表：常见元件的 I-V 特性
LDR (light-dependent resistor): resistance decreases as light intensity increases. Thermistor: resistance decreases as temperature increases. Both are used in sensing circuits.
光敏电阻 (LDR)：光照增强时电阻减小。热敏电阻：温度升高时电阻减小。两者都常用于传感电路。
6. Magnetism and Electromagnetism | 磁学与电磁学
A magnet has a north and a south pole. Like poles repel, unlike poles attract. Magnetic field lines go from north to south.
磁体有 N 极和 S 极。同名磁极相互排斥，异名磁极相互吸引。磁感线从 N 极指向 S 极。
An electromagnet is a solenoid with a soft iron core; the magnetic field strength increases with more turns, larger current, or an iron core.
电磁铁是带有软铁芯的螺线管；增加匝数、增大电流或加入铁芯均可增强磁场强度。
The motor effect: a current-carrying wire in a magnetic field experiences a force. Fleming’s left-hand rule gives direction: thumb = force, first finger = field, second finger = current.
电动机效应：置于磁场中的载流导体会受到力的作用。弗莱明左手定则判断方向：拇指—力，食指—磁场，中指—电流。
A d.c. motor uses a split-ring commutator to reverse current direction every half turn, keeping the coil spinning in one direction.
直流电动机利用换向器每半圈改变电流方向，从而使线圈持续朝同一方向转动。
Electromagnetic induction: a changing magnetic field induces a p.d. across a conductor. For a generator, moving a coil in a magnetic field produces a.c.; slip rings maintain a.c. output.
电磁感应：变化的磁场会使导体两端产生感应电压。在发电机中，线圈在磁场中转动产生交流电，集电环保持交流输出。
Transformers change the voltage of an a.c. supply: Vp/Vs = Np/Ns. A step-up transformer has more turns on the secondary coil and increases voltage.
变压器改变交流电压：Vp/Vs = Np/Ns。升压变压器的副线圈匝数更多，用于升高电压。
7. Thermal Physics | 热物理学
Temperature (measured in °C or K) reflects the average kinetic energy of particles. Heat is thermal energy transferred due to a temperature difference.
温度（单位为 °C 或 K）反映了粒子平均动能的大小。热量是因温度差而传递的热能。
Heat transfer methods: conduction (mainly in solids, via particles or free electrons), convection (fluids, via density changes), and radiation (infrared, does not need a medium).
热传递的方式：热传导（主要发生在固体中，通过粒子振动或自由电子），热对流（流体中，因密度差异而流动），热辐射（通过红外线，不需要介质）。
Specific heat capacity c: energy needed to raise 1 kg of a substance by 1 °C. ΔE = m c Δθ. Water has a high specific heat capacity (4200 J/kg°C).
比热容 c：使 1 kg 物质升高 1 °C 所需的能量。ΔE = m c Δθ。水的比热容很高 (4200 J/kg°C)。
Specific latent heat L: energy needed to change the state of 1 kg of a substance without temperature change. E = m L. Latent heat of fusion (melting) and vaporisation (boiling) are key values.
比潜热 L：使 1 kg 物质在不改变温度的情况下发生状态变化所需的能量。E = m L。熔化潜热和汽化潜热是重要的常数。
Gas pressure is caused by particles colliding with container walls. Increasing temperature at constant volume raises pressure because particles move faster and hit walls harder and more often.
气体压强是由粒子碰撞容器壁产生的。在体积不变时，温度升高会使粒子运动更快，碰撞更有力、更频繁，因此压强增大。
8. Atomic Physics | 原子物理
An atom consists of a nucleus containing protons and neutrons, surrounded by electrons in energy levels. Proton number Z = atomic number, nucleon number A = mass number.
原子由包含质子和中子的原子核以及分层排布的电子组成。质子数 Z = 原子序数，核子数 A = 质量数。
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, e.g., ¹⁴₆C and ¹²₆C.
同位素是具有相同质子数但中子数不同的同种元素原子，例如 ¹⁴₆C 和 ¹²₆C。
Radioactive decay: unstable nuclei emit alpha (α, ⁴₂He), beta (β⁻, electron), or gamma (γ, electromagnetic wave) radiation. Alpha is the most ionising but least penetrating; gamma is the most penetrating.
放射性衰变：不稳定的原子核发射 α 粒子（⁴₂He）、β⁻ 粒子（电子）或 γ 射线（电磁波）。α 电离能力最强但穿透力最弱，γ 穿透力最强。
Half-life is the time taken for half the radioactive nuclei in a sample to decay. It is constant for a given isotope and is used in carbon dating.
半衰期是样本中一半的放射性原子核发生衰变所需的时间。对于特定同位素，半衰期是恒定的，可用于碳年代测定。
Nuclear fission: a heavy nucleus (e.g., U-235) splits into two smaller nuclei, releasing energy and neutrons, which can trigger a chain reaction.
核裂变：重核（如铀-235）分裂成两个较小的核，释放能量和中子，可能引发链式反应。
Nuclear fusion: two light nuclei (e.g., hydrogen isotopes) join to form a heavier nucleus, releasing vast energy. It occurs in stars.
核聚变：两个轻核（如氢的同位素）结合成一个较重的核，释放巨大能量。聚变发生在恒星内部。
9. Space Physics | 空间物理
Our Solar System contains the Sun, eight planets, dwarf planets, moons, asteroids, and comets. Orbital period depends on distance from the Sun; planets sweep out equal areas in equal times under gravity.
太阳系包括太阳、八大行星、矮行星、卫星、小行星和彗星。公转周期取决于与太阳的距离；在引力作用下，行星在相等时间内扫过相等面积。
The life cycle of a star depends on its mass. A star like the Sun: nebula → protostar → main sequence → red giant → planetary nebula → white dwarf. More massive stars become red supergiants and may end as supernovae, leaving behind neutron stars or black holes.
恒星的生命周期取决于质量。类似太阳的恒星：星云 → 原恒星 → 主序星 → 红巨星 → 行星状星云 → 白矮星。更大质量的恒星成为红超巨星，可能以超新星爆发结束，留下中子星或黑洞。
Red-shift: light from distant galaxies is shifted toward the red end of the spectrum, indicating they are moving away from us. More distant galaxies show greater red-shift, evidence for an expanding Universe.
红移：来自遥远星系的光谱向红端移动，表明它们正在远离我们。越远的星系红移越大，这为宇宙膨胀提供了证据。
The Big Bang theory states the Universe began from a hot, dense point and has been expanding ever since. Cosmic microwave background radiation supports this.
大爆炸理论认为宇宙起源于一个极热、极密的点，并一直在膨胀。宇宙微波背景辐射为该理论提供了支持。
10. Practical Skills | 实验技能
Always record measurements with appropriate units and to an appropriate precision. Use a ruler to measure length, a stopwatch for time, an ammeter in series for current, and a voltmeter in parallel for p.d.
始终记录带有正确单位和适当精度的测量值。用刻度尺测量长度，秒表测时间，电流表串联测电流，电压表并联测电压。
Avoid parallax error by reading the scale with your eye directly perpendicular to the pointer. Repeat readings and calculate a mean to reduce random error.
读数时视线应与刻度垂直，以避免视差。通过重复测量并计算平均值来减小随机误差。
Plot graphs with labelled axes, sensible scales, and plot points as small crosses. Draw a line of best fit; if it passes through the origin, it suggests a direct proportionality.
绘制图表时应标记坐标轴、选用合理的刻度，并用小十字标出数据点。画出最佳拟合线；如果该线通过原点，则表明存在正比关系。
When describing an investigation, clearly state the independent variable (you change), dependent variable (you measure), and control variables (keep constant).
描述探究实验时，应明确说明自变量（你改变的）、因变量（你测量的）和控制变量（保持不变的）。
Understand the use of standard circuit tests: measuring resistance via V/I, investigating factors affecting resistance, or determining the half-life from a decay curve using a Geiger-Müller tube.
理解常用电路测试：通过 V/I 测量电阻、探究影响电阻的因素，或使用盖革-米勒计数管从衰变曲线图中确定半衰期。
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