📚 IGCSE OCR Physics: High-Frequency Topic Summary | IGCSE OCR 物理：高频考点总结
Welcome to this comprehensive revision guide covering the most frequently tested topics in IGCSE OCR Physics. These key concepts are essential for exam success, from motion and forces to electricity and waves. Each section provides concise explanations in both English and Chinese, key formulas, and important exam tips.
欢迎阅读这份全面复习指南，涵盖IGCSE OCR物理中最常考的主题。从运动与力到电学与波动，这些关键概念对于考试成功至关重要。每个部分都提供了简洁的中英双语解释、关键公式和重要的应试提示。
1. Motion | 运动学
Speed is the distance travelled per unit time: speed = distance / time (v = d / t). It is a scalar quantity. Velocity is speed in a given direction and is a vector. Acceleration is the rate of change of velocity: a = (v – u) / t, where u is the initial velocity, v is the final velocity, and t is the time taken.
速率是单位时间内移动的距离：速率 = 距离 / 时间 (v = d / t)，是标量。速度是带有方向的速率，是矢量。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 为时间。
Distance-time graphs: gradient = speed; a horizontal line means the object is stationary. Velocity-time graphs: gradient = acceleration; area under the graph = displacement. Be able to calculate acceleration from a velocity-time graph and total distance travelled from the area.
距离-时间图：斜率 = 速率；水平线代表物体静止。速度-时间图：斜率 = 加速度；图线下方面积 = 位移。要能根据速度-时间图计算加速度，并根据面积求出总路程。
v = d / t; a = (v – u) / t
2. Forces and Newton’s Laws | 力与牛顿定律
A force can change an object’s shape, speed or direction. Newton’s First Law states that an object remains at rest or moves with constant velocity unless acted on by a resultant force. Newton’s Second Law links force, mass and acceleration: F = m × a (resultant force = mass × acceleration).
力可以改变物体的形状、速度或方向。牛顿第一定律指出，若不受合力作用，物体将保持静止或匀速直线运动。牛顿第二定律将力、质量和加速度联系起来：F = m × a (合力 = 质量 × 加速度)。
Newton’s Third Law: when two objects interact, they exert equal and opposite forces on each other. These forces act on different objects. Example: a book on a table – the book pushes down on the table, and the table pushes up on the book with an equal force.
牛顿第三定律：两个物体相互作用时，彼此施加的力大小相等、方向相反，且作用在不同物体上。示例：放在桌上的书——书向下压桌子，桌子以同样大小的力向上支持书。
Weight is the force of gravity on a mass: W = m × g (g ≈ 10 N/kg on Earth). Mass is measured in kg, weight in newtons (N).
重量是重力对物体质量的拉力：W = m × g (地球表面 g ≈ 10 N/kg)。质量单位为 kg，重量单位为牛 (N)。
3. Momentum | 动量
Momentum p is defined as p = m × v. It is a vector quantity, so direction matters. In a closed system, total momentum before a collision or explosion equals total momentum after (conservation of momentum).
动量 p 定义为 p = m × v，是矢量，方向不可忽略。在封闭系统内，碰撞或爆炸前的总动量等于碰撞后的总动量（动量守恒）。
The change in momentum is related to impulse: impulse = F × t = Δp. Force is the rate of change of momentum. Safety features like airbags and crumple zones increase the impact time, reducing the force on occupants.
动量变化与冲量的关系为：冲量 = F × t = Δp。力等于动量的变化率。安全气囊和溃缩区等设计通过延长碰撞时间，减小乘客所受的力。
p = m × v; F × t = m × (v – u)
4. Energy, Work and Power | 能量、功与功率
Energy cannot be created or destroyed, only transferred or stored. Main energy stores: kinetic, gravitational potential, chemical, elastic, nuclear, thermal. Energy can be transferred by forces (work), heating, or waves.
能量既不会凭空产生也不会消灭，只能转移或储存。主要能量储存形式：动能、重力势能、化学能、弹性势能、核能和热能。能量可通过力（做功）、加热或波的方式进行转移。
Work done = force × distance moved in the direction of the force: W = F × d. Power is the rate of doing work: P = W / t. Efficiency = (useful energy output / total energy input) × 100%.
做功 = 力 × 沿力方向移动的距离：W = F × d。功率是做功的速率：P = W / t。效率 = (有用能量输出 / 总能量输入) × 100%。
Gravitational potential energy: GPE = m × g × h. Kinetic energy: KE = ½ × m × v². You must be able to apply these equations in problems involving energy transfers, such as falling objects or roller coasters.
重力势能：GPE = m × g × h。动能：KE = ½ × m × v²。需要能运用这些方程解决诸如落体运动或过山车中的能量转化问题。
5. Pressure | 压强
Pressure is defined as force per unit area: P = F / A. The unit is pascal (Pa), where 1 Pa = 1 N/m². A small force over a small area can produce high pressure (e.g., a sharp nail).
压强定义为单位面积上的力：P = F / A。单位是帕斯卡 (Pa)，1 Pa = 1 N/m²。在小面积上施加较小的力也可以产生高压 (如尖钉)。
In a fluid (liquid or gas), pressure increases with depth: pressure due to a column of liquid = h × ρ × g, where h is depth, ρ is density of the fluid, and g is gravitational field strength. Atmospheric pressure decreases with altitude.
在流体（液体或气体）中，压强随深度增加而增大：液柱压强 = h × ρ × g，其中 h 为深度，ρ 为流体密度，g 为重力场强度。大气压随海拔升高而减小。
Hydraulic systems use the transmission of pressure in an incompressible liquid to multiply force: P₁ = P₂ gives F₁ / A₁ = F₂ / A₂.
液压系统利用不可压缩液体中压强的传递来放大力量：由 P₁ = P₂ 可得 F₁ / A₁ = F₂ / A₂。
6. Waves | 波
Waves transfer energy without transferring matter. There are two main types: transverse waves (e.g., light, water ripples) where oscillations are perpendicular to the direction of energy transfer, and longitudinal waves (e.g., sound) where oscillations are parallel.
波传播能量而不传播物质。主要有两类：横波（如光、水波），振动方向与能量传播方向垂直；纵波（如声波），振动方向与能量传播方向平行。
The wave equation links speed, frequency and wavelength: v = f × λ. Frequency f is measured in hertz (Hz), wavelength λ in metres, and speed v in m/s. The period T = 1 / f.
波速方程将波速、频率和波长联系起来：v = f × λ。频率 f 的单位是赫兹 (Hz)，波长 λ 单位为米，波速 v 单位是 m/s。周期 T = 1 / f。
Reflection: angle of incidence = angle of reflection. Refraction occurs when waves change speed at a boundary, causing a change in direction if the wave enters at an angle. Snell’s Law: n = sin i / sin r. Total internal reflection occurs when the angle of incidence exceeds the critical angle.
反射：入射角 = 反射角。当波在界面处改变速度时发生折射，若以一定角度入射，传播方向发生改变。斯涅尔定律：n = sin i / sin r。当入射角大于临界角时发生全内反射。
7. Electromagnetic Spectrum | 电磁波谱
The electromagnetic spectrum, in order of increasing frequency and decreasing wavelength: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. All travel at the same speed in a vacuum, c = 3.0 × 10⁸ m/s.
电磁波谱按频率递增、波长递减的顺序为：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传播速度相同，c = 3.0 × 10⁸ m/s。
Uses depend on wavelength and energy: radio for communication; microwaves for cooking and satellite signals; infrared for thermal imaging and remote controls; visible light for vision; ultraviolet for fluorescent lamps and sterilisation; X-rays for medical imaging; gamma rays for cancer treatment and sterilising equipment.
不同波段的用途取决于波长和能量：无线电波用于通信；微波用于烹饪和卫星信号；红外线用于热成像和遥控；可见光用于视觉；紫外线用于日光灯和消毒；X 射线用于医学影像；伽马射线用于癌症治疗和器械灭菌。
Higher-frequency EM radiation also carries more photon energy, which can be dangerous: UV can cause skin cancer, X-rays and gamma rays are ionising and can damage cells.
频率越高的电磁辐射光子能量越大，可能具有危害：紫外线可致皮肤癌，X 射线和伽马射线具有电离能力，能损伤细胞。
8. Electricity Basics | 电学基础
Electric current is the rate of flow of charge: I = Q / t, where Q is charge in coulombs (C) and t is time in seconds. By convention, current flows from positive to negative. In metals, current is due to the movement of electrons.
电流是电荷的流动速率：I = Q / t，其中 Q 为电荷量 (C)，t 为时间 (s)。通常规定电流方向为正电荷的移动方向；在金属中，电流源于电子的定向移动。
Potential difference (voltage) is the energy transferred per unit charge: V = E / Q. Resistance is the opposition to current: R = V / I (Ohm’s Law). Resistance of a wire depends on its length, cross-sectional area and material: R = ρ × L / A.
电势差（电压）是单位电荷转移的能量：V = E / Q。电阻是对电流的阻碍作用：R = V / I (欧姆定律)。导线的电阻取决于长度、横截面积和材料：R = ρ × L / A。
Electrical power can be expressed in several ways: P = I × V, P = I² × R, P = V² / R. Energy transferred: E = P × t = I × V × t.
电功率有多种表达形式：P = I × V，P = I² × R，P = V² / R。能量转移：E = P × t = I × V × t。
9. Circuit Analysis | 电路分析
In a series circuit, current is the same at all points. The total resistance is the sum of individual resistances: R_total = R₁ + R₂ + … The supply voltage is shared: V_total = V₁ + V₂ + … Adding more resistors increases total resistance and reduces current.
在串联电路中，各处电流相等。总电阻等于各电阻之和：R_total = R₁ + R₂ + … 电源电压由各元件分担：V_total = V₁ + V₂ + … 增加电阻会增大总电阻，减小电流。
In a parallel circuit, the voltage across each branch is the same as the supply voltage. The total current is the sum of branch currents: I_total = I₁ + I₂ + … Total resistance is less than the smallest individual resistance: 1/R_total = 1/R₁ + 1/R₂ + … Adding more parallel branches decreases total resistance and increases total current.
在并联电路中，各支路两端电压相等，且等于电源电压。总电流等于各支路电流之和：I_total = I₁ + I₂ + … 总电阻小于任一单独电阻：1/R_total = 1/R₁ + 1/R₂ + … 增加并联支路会降低总电阻，增大总电流。
Be able to design circuits with ammeters (in series) and voltmeters (in parallel). LDRs and thermistors are variable resistors: an LDR’s resistance decreases with light intensity; a thermistor’s resistance typically decreases as temperature rises.
要能设计含有电流表（串联）和电压表（并联）的电路。光敏电阻 (LDR) 和热敏电阻是可变电阻：LDR 的电阻随光照增强而减小；热敏电阻的电阻通常随温度升高而减小。
10. Magnetism and Electromagnetism | 磁与电磁
Permanent magnets have north and south poles; like poles repel, unlike poles attract. A magnetic field line shows the direction of force on a north pole, going from north to south outside the magnet.
永磁体有 N 极和 S 极；同名极相斥，异名极相吸。磁感线表示 N 极受力的方向，在磁体外部从 N 指向 S。
An electric current produces a magnetic field – this is the motor effect. The force on a current-carrying conductor in a magnetic field is given by Fleming’s left-hand rule. The force is largest when the current is perpendicular to the field: F = B × I × L (for a straight wire at right angles).
电流能产生磁场——这是电动机效应。磁场中通电导体受力的方向可由弗莱明左手定则判断。当电流方向与磁场垂直时受力最大：F = B × I × L（适用于直导线垂直切割磁感线的情况）。
Electromagnetic induction: a changing magnetic field can induce a voltage in a conductor. This is the generator effect. A transformer uses this to change alternating voltages: V_p / V_s = N_p / N_s, for an ideal transformer the input power equals output power: V_p × I_p = V_s × I_s.
电磁感应：变化的磁场可以在导体中产生感应电压，即发电机效应。变压器利用此原理改变交流电压：V_p / V_s = N_p / N_s，对于理想变压器，输入功率等于输出功率：V_p × I_p = V_s × I_s。
11. Thermal Physics | 热物理学
Heat can be transferred by conduction (mainly in solids, through vibrating particles and free electrons), convection (in fluids, by movement of the fluid itself), and radiation (via infrared waves, can travel through vacuum).
热量可通过传导（主要在固体中，通过粒子振动和自由电子传递）、对流（在流体中，通过流体自身的运动）和辐射（以红外波形式，可在真空中传播）进行传递。
When a substance is heated, its temperature rise depends on its mass, specific heat capacity c, and energy supplied: Q = m × c × Δθ. A material with a high specific heat capacity requires more energy to raise its temperature.
物质受热后，其升高的温度取决于质量、比热容 c 和提供的能量：Q = m × c × Δθ。比热容较大的物质升温需要更多的能量。
During a change of state (melting, boiling), temperature remains constant while energy is absorbed or released. The energy needed for a change of state is given by latent heat: Q = m × L (L_f for fusion, L_v for vaporisation).
在状态变化（熔化、沸腾）过程中，温度保持不变，同时能量被吸收或释放。状态变化所需的能量由潜热公式给出：Q = m × L（熔化潜热 L_f，汽化潜热 L_v）。
12. Radioactivity | 放射性
Atoms consist of a nucleus (protons + neutrons) surrounded by electrons. Unstable nuclei emit radiation to become more stable. There are three main types: alpha (α) particles – helium nuclei, strongly ionising, stopped by paper; beta (β) particles – fast electrons, moderately ionising, stopped by a few mm of aluminium; gamma (γ) rays – electromagnetic waves, weakly ionising, reduced by thick lead or concrete.
原子由原子核（质子+中子）和绕核运动的电子组成。不稳定的原子核通过释放辐射变得稳定。主要有三种辐射：α 粒子——氦核，电离能力最强，可被纸张挡住；β 粒子——高速电子，电离能力中等，几毫米铝板即可阻挡；γ 射线——电磁波，电离能力最弱，需厚铅板或混凝土才能减弱。
Radioactive decay is random, but the half-life t½ is the time taken for half the radioactive nuclei in a sample to decay. After n half-lives, the remaining fraction is (½)ⁿ. Be able to interpret decay curves.
放射性衰变是随机的，但半衰期 t½ 指样品中一半的放射性原子核发生衰变所需的时间。经过 n 个半衰期后，剩余比例为 (½)ⁿ。要能解读衰变曲线。
Background radiation comes from natural sources (rocks, cosmic rays) and artificial sources (medical, nuclear power). Safety precautions include using tongs, keeping sources at a distance, and shielding.
背景辐射来自天然来源（岩石、宇宙射线）和人造来源（医疗、核能）。安全措施包括使用镊子操作、远距离存放放射源以及屏蔽。
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