IGCSE Cambridge Physics | 剑桥 IGCSE 物理核心概念复习

📚 IGCSE Cambridge Physics | 剑桥 IGCSE 物理核心概念复习

This revision guide covers the essential topics for the Cambridge IGCSE Physics syllabus (0625), including measurement, mechanics, thermal physics, waves, electricity, magnetism, and atomic physics. It is designed to help you consolidate key ideas, memorise important formulas, and avoid common mistakes before your exam.

本复习指南覆盖剑桥 IGCSE 物理大纲（0625）的核心主题，包括测量、力学、热学、波、电学、磁学与原子物理。它帮助你整合关键概念、记忆重要公式，并在考前避开常见错误。

1. Measurement & Units | 测量与单位

Physics starts with measurement. The Cambridge IGCSE syllabus uses the International System of units (SI). You must be able to choose the correct instrument for a given measurement:

物理始于测量。剑桥 IGCSE 大纲采用国际单位制（SI）。你必须能为给定测量选择正确的仪器：

Length: metre rule (short distances), vernier callipers (to 0.1 mm), micrometer (to 0.01 mm).
长度：米尺测短距离，游标卡尺精确到 0.1 mm，千分尺精确到 0.01 mm。
Mass: electronic balance; Time: stopwatch; Volume: measuring cylinder.
质量用电子天平；时间用秒表；体积用量筒。
An electronic stopwatch has a typical human reaction error of about 0.1 s to 0.5 s.
电子秒表存在约 0.1 s 至 0.5 s 的人体反应误差。

Average speed = total distance / total time

平均速度 = 总路程 / 总时间

For very small lengths, use micrometres (µm) and nanometres (nm). Conversion: 1 cm = 10⁻² m, 1 mm = 10⁻³ m, 1 µm = 10⁻⁶ m, 1 nm = 10⁻⁹ m.

对于微小长度，使用微米（µm）和纳米（nm）。换算关系：1 cm = 10⁻² m，1 mm = 10⁻³ m，1 µm = 10⁻⁶ m，1 nm = 10⁻⁹ m。

Quantity 物理量	Unit 单位	Symbol 符号
Mass 质量	kilogram 千克	kg
Length 长度	metre 米	m
Time 时间	second 秒	s
Current 电流	ampere 安培	A
Temperature 温度	kelvin 开尔文	K

2. Mechanics – Motion & Forces | 力学：运动与力

Motion is described using distance, displacement, speed, velocity, and acceleration. Displacement is a vector (has direction); distance is a scalar (magnitude only).

运动用距离、位移、速度、速率和加速度来描述。位移是矢量（有方向），距离是标量（仅有大小）。

v = s / t, a = (v – u) / t

v = s / t，a = (v – u) / t

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 distance.

在位移-时间图中，斜率表示速度；在速度-时间图中，斜率表示加速度，图线与坐标轴围成的面积表示距离。

Newton’s three laws are central:

牛顿三大定律是核心内容：

First law: an object stays at rest or moves at constant velocity unless acted on by a resultant force.
第一定律：若不受合力作用，物体保持静止或匀速直线运动。
Second law: F = m a, where F is the resultant force in newtons.
第二定律：F = m a，式中 F 为合力，单位牛顿。
Third law: every action has an equal and opposite reaction.
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。

Resultant force = mass × acceleration

合力 = 质量 × 加速度

Weight is the force of gravity on an object: W = m g. On Earth, g ≈ 10 N/kg or 10 m/s².

重力是地球对物体的引力：W = m g。地球上，g ≈ 10 N/kg 或 10 m/s²。

3. Work, Energy & Power | 功、能与功率

Work is done when a force moves an object over a distance in the direction of the force.

当力使物体沿力的方向移动一段距离时，力就做了功。

W = F s, P = W / t

W = F s，P = W / t

Energy is measured in joules (J). The main forms of mechanical energy you need are kinetic energy and gravitational potential energy:

能量单位是焦耳（J）。你需要掌握的两种主要机械能是动能和重力势能：

Eₖ = ½ m v², Eₚ = m g h

Eₖ = ½ m v²，Eₚ = m g h

The principle of conservation of energy states: energy cannot be created or destroyed, only converted from one form to another. In ideal cases, loss of Eₚ equals gain of Eₖ.

能量守恒定律指出：能量既不会凭空产生，也不会凭空消失，只能从一种形式转化为另一种形式。在理想情况下，重力势能的减少等于动能的增加。

Power is the rate of work done:

功率是做功的快慢：

P = W / t = F v

Efficiency is always less than 100% in real machines. Efficiency = (useful output energy / total input energy) × 100%.

实际机器的效率总是小于 100%。效率 =（有用输出能量 / 总输入能量）× 100%。

4. Thermal Physics | 热学

Heating changes the internal energy of a material, which is related to the kinetic and potential energy of its particles.

加热会改变物体的内能，内能与粒子动能和势能有关。

Q = m c ΔT

Here Q is thermal energy (J), m is mass, c is specific heat capacity, and ΔT is the temperature change.

其中 Q 是热量（J），m 是质量，c 是比热容，ΔT 是温度变化量。

The three states of matter are solid, liquid and gas. During a change of state, temperature stays constant because energy is used to break or form intermolecular bonds.

物质的三种状态是固态、液态和气态。在状态变化过程中，温度保持不变，因为能量用于破坏或形成分子间作用力。

Process 过程	Direction 方向	Energy 能量
Melting 熔化	Solid → Liquid	Absorbed 吸热
Boiling 沸腾	Liquid → Gas	Absorbed 吸热
Condensation 液化	Gas → Liquid	Released 放热
Freezing 凝固	Liquid → Solid	Released 放热

5. Waves & Light | 波与光

Waves transfer energy without transferring matter. They can be transverse or longitudinal. Light is a transverse wave; sound is a longitudinal wave.

波传递能量但不传递物质。波分为横波和纵波。光是横波，声音是纵波。

v = f λ

v is wave speed (m/s), f is frequency (Hz), λ is wavelength (m). For electromagnetic waves in vacuum, v = 3.0 × 10⁸ m/s.

v 是波速（m/s），f 是频率（Hz），λ 是波长（m）。电磁波在真空中速度 v = 3.0 × 10⁸ m/s。

Reflection and refraction are key for light. Snell’s law links angles and refractive index:

反射和折射是光学的关键内容。斯涅耳定律联系了角度和折射率：

n = sin i / sin r

When light passes from glass to air and the angle of incidence exceeds the critical angle, total internal reflection occurs. This is used in optical fibres.

当光从玻璃射入空气且入射角大于临界角时，会发生全内反射。这一原理用于光纤通信。

The electromagnetic spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. Higher frequency means higher energy.

电磁波谱包括无线电波、微波、红外线、可见光、紫外线、X 射线和伽马射线。频率越高，能量越大。

6. Electricity & Circuits | 电学与电路

Electric current is the rate of flow of charge. Charge is measured in coulombs (C), current in amperes (A), and potential difference in volts (V).

电流是电荷流动的速率。电荷单位是库仑（C），电流单位是安培（A），电压单位是伏特（V）。

Q = I t, V = I R, P = V I

Q = I t，V = I R，P = V I

In a series circuit, current is the same everywhere and voltages add. In a parallel circuit, voltage is the same across each branch and currents add.

在串联电路中，电流处处相等，电压相加；在并联电路中，各支路电压相等，电流相加。

Resistors in series and parallel:

串并联电阻计算：

R = R₁ + R₂; 1/R = 1/R₁ + 1/R₂

R = R₁ + R₂；1/R = 1/R₁ + 1/R₂

For electrical safety, a fuse is a thin wire that melts and breaks the circuit if current is too high. A double insulation prevents live wires touching the case.

为保证用电安全，保险丝是在电流过大时熔断并切断电路的细导线；双重绝缘防止火线接触外壳。

7. Magnetism & Electromagnetism | 磁与电磁

Magnets have two poles, north (N) and south (S), and attract magnetic materials such as iron and steel. Opposites attract; like poles repel.

磁体有两个磁极：北极（N）和南极（S），能吸引铁、钢等磁性材料。异名磁极相互吸引，同名磁极相互排斥。

An electric current produces a magnetic field. Increasing the current or number of turns in a coil strengthens the electromagnet.

电流会产生磁场。增大电流或增加线圈匝数可以增强电磁铁。

Electromagnetic induction: when a conductor cuts magnetic field lines, a potential difference is induced. The direction of the induced current opposes the change producing it (Lenz’s law).

电磁感应：当导体切割磁感线时，会产生感应电压。感应电流的方向总是阻碍引起它的磁通量变化（楞次定律）。

Vₚ / Vₛ = Nₚ / Nₛ

Transformers use alternating current (a.c.) to step voltage up or down. They only work with a.c. because a changing magnetic field is required.

变压器利用交流电（a.c.）来升压或降压。它只能使用交流电，因为需要变化的磁场。

8. Atomic Physics & Radioactivity | 原子物理与放射性

An atom has a small, dense nucleus containing protons and neutrons, surrounded by electrons. The atomic number is the number of protons; the mass number is protons plus neutrons.

原子由微小的致密原子核（含质子和中子）及核外电子构成。原子序数是质子数，质量数是质子数加中子数。

Radioactive decay is random and spontaneous. There are three main types:

放射性衰变是随机、自发的。主要有三种辐射类型：

Alpha (α): helium nucleus, molar mass 4, stopped by paper or skin, strong ionising power.
阿尔法（α）：氦核，质量数 4，可被纸张或皮肤阻挡，电离能力强。
Beta (β): electron, stopped by aluminium, medium ionising power.
贝塔（β）：电子，可被铝板阻挡，电离能力中等。
Gamma (γ): electromagnetic wave, needs thick lead or concrete, weak ionising power.
伽马（γ）：电磁波，需要厚铅或混凝土阻挡，电离能力弱。

Half-life is the time taken for half of the unstable nuclei to decay.

半衰期是放射性核数量减少一半所需的时间。

N = N₀ (½)^(t / T½)

Nuclear fission is the splitting of a large nucleus, releasing energy. Nuclear fusion joins small nuclei, releasing even more energy.

核裂变是重核分裂并释放能量的过程；核聚变是轻核结合并释放更多能量的过程。

9. Exam Strategies | 应考策略

Read every command word carefully. ‘State’ requires a short answer; ‘explain’ needs a reason; ‘calculate’ needs a full working and correct unit.

仔细阅读每一个指令词。”State（写出）” 只需简短回答；”Explain（解释）” 需要理由；”Calculate（计算）” 需要完整过程和正确单位。

Always include units in your final answer. Missing units lose marks.
答案务必包含单位。漏写单位会失分。
Show every step of your working in calculations, even if the final answer is wrong, you can still earn method marks.
计算题要写出每一步过程，即使最终答案错误，仍可能获得步骤分。
Draw circuit diagrams and force diagrams with a ruler. A straight line represents a wire; a rectangle represents a resistor.
绘制电路图和受力图时必须使用直尺。直线代表导线，矩形代表电阻。
For graph questions, label axes with quantities, units, and use a sharp pencil.
做图题时，坐标轴要标注物理量和单位，并削尖铅笔作图。

Time management: allocate about 1.5 minutes per mark. Do not spend too long on one question.

时间管理：大约每分 1.5 分钟。不要在一道题上停留太久。

10. Common Mistakes to Avoid | 常见错误对照

Many candidates lose marks because of careless errors. Check the table below before your exam.

很多考生因粗心错误而失分。考前请检查下面这张表格。

Common Mistake 常见错误	Correct Approach 正确做法
Confusing mass and weight	Mass is kg; weight is N, W = mg
混淆质量与重力	质量单位 kg；重力单位 N，W = mg
Forgetting that sound cannot travel in vacuum	Sound needs a medium; light does not
忘记声音不能在真空中传播	声音需要介质；光不需要
Using V = I R for a.c. transformers	Use turns ratio for transformers
在变压器题中套用 V = I R	变压器用匝数比公式
Omitting direction in vector answers	Write both magnitude and direction
矢量答案漏写方向	要同时写出大小和方向

Finally, keep a clear formula list on your revision sheet and practise past papers under timed conditions.

最后，在复习薄上整理一份清晰的公式清单，并在限时条件下练习历年真题。

Good luck with your Cambridge IGCSE Physics exam!

祝你剑桥 IGCSE 物理考试顺利！

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IGCSE Cambridge Physics | 剑桥 IGCSE 物理核心概念复习