📚 IGCSE CCEA Science: Electricity and Magnetism Key Points Review | IGCSE CCEA 科学：电与磁 考点精讲
Welcome to this comprehensive review of the Electricity and Magnetism topics for the IGCSE CCEA Science specification. These concepts form a core part of physics and are essential for understanding how modern technology works, from household wiring to generating electricity. This article summarises the key learning points, definitions, laws and applications you must know for the examination.
欢迎阅读这篇针对 IGCSE CCEA 科学大纲中电与磁部分的全面复习。这些概念是物理学的核心，对于从家庭电路到发电的现代技术理解至关重要。本文总结了考试必须掌握的关键知识点、定义、定律和应用。
1. Electric Charge and Static Electricity | 电荷与静电
All matter is made of atoms that contain protons (+), neutrons (neutral) and electrons (-).
所有物质由原子组成，原子包含带正电的质子、不带电的中子和带负电的电子。
An object becomes charged by gaining or losing electrons. Gaining electrons gives a negative charge; losing electrons gives a positive charge.
物体通过得到或失去电子而带电。得到电子带负电；失去电子带正电。
Like charges repel, unlike charges attract. This electrostatic force acts without contact.
同种电荷相斥，异种电荷相吸。这种静电力无需接触就能作用。
Static electricity is generated by friction when insulating materials are rubbed together, e.g. a polythene rod rubbed with a cloth becomes negatively charged because it gains electrons.
静电荷通过摩擦产生，当绝缘材料相互摩擦时，例如用布摩擦聚乙烯棒，棒因获得电子而带负电。
Common applications include electrostatic paint spraying and photocopiers. Dangers include sparks causing fires or explosions when refuelling aircraft.
常见应用包括静电喷涂和复印机。危险包括飞机加油时火花引起火灾或爆炸。
Earthing (connecting to ground) allows charge to flow away safely, preventing build-up.
接地（连至大地）使电荷安全导走，防止积聚。
2. Current, Voltage and Resistance | 电流、电压与电阻
Electric current (I) is the rate of flow of electric charge. It is measured in amperes (A) using an ammeter connected in series.
电流 (I) 是电荷流动的速率。用安培计串联测量，单位为安培 (A)。
Voltage (V), or potential difference, is the energy transferred per unit charge. It is measured in volts (V) using a voltmeter connected in parallel.
电压 (V) 或电势差是单位电荷转移的能量。用电压表并联测量，单位为伏特 (V)。
Resistance (R) is the opposition to current flow, measured in ohms (Ω). A resistor’s resistance depends on its length (longer = higher R), cross-sectional area (larger area = lower R), material and temperature.
电阻 (R) 是对电流的阻碍，以欧姆 (Ω) 为单位。电阻取决于长度（越长电阻越大）、横截面积（面积越大电阻越小）、材料和温度。
For a metallic conductor, resistance increases with temperature. For a thermistor, resistance decreases with temperature. An LDR (light-dependent resistor) decreases resistance as light intensity increases.
对于金属导体，电阻随温度升高而增大；对于热敏电阻，电阻随温度升高而减小；光敏电阻 (LDR) 在光照增强时电阻减小。
3. Ohm’s Law and V=IR | 欧姆定律与 V=IR
Ohm’s Law states that for a metallic conductor at constant temperature, the current through it is directly proportional to the potential difference across it.
欧姆定律指出，对于恒温下的金属导体，通过它的电流与两端电势差成正比。
V = I × R
V: voltage (V), I: current (A), R: resistance (Ω)
V：电压 (V)，I：电流 (A)，R：电阻 (Ω)
An ohmic conductor (e.g. a fixed resistor at constant temperature) gives a straight-line I-V graph passing through the origin.
欧姆导体（如恒温下的固定电阻）的 I-V 图是一条过原点的直线。
Non-ohmic conductors include a filament lamp (curve flattens as resistance increases with heat) and a diode (current flows only in one direction, high resistance in reverse).
非欧姆导体包括灯丝灯泡（曲线变平，因发热电阻增大）和二极管（电流仅单向导通，反向电阻极高）。
4. Series and Parallel Circuits | 串联与并联电路
In a series circuit, there is only one path for the current. In a parallel circuit, there are multiple paths.
在串联电路中，电流只有一条路径；在并联电路中，有多条路径。
The following table compares the key properties.
下表比较了关键特性。
| Feature | Series Circuit | Parallel Circuit |
|---|---|---|
| Current | Same everywhere | Total current = sum of branch currents |
| Voltage | Shared across components | Same across each branch |
| Resistance | R_total = R₁ + R₂ + … | 1/R_total = 1/R₁ + 1/R₂ + … |
| 特性 | 串联电路 | 并联电路 |
|---|---|---|
| 电流 | 处处相等 | 总电流 = 各支路电流之和 |
| 电压 | 各元件分压 | 各支路电压相等 |
| 电阻 | R总 = R₁ + R₂ + … | 1/R总 = 1/R₁ + 1/R₂ + … |
Adding more resistors in series increases total resistance; adding more in parallel decreases total resistance because extra paths are provided for current.
串联增加电阻会增大总电阻；并联增加电阻会减小总电阻，因为提供了更多电流路径。
5. Electrical Power and Energy | 电功率与电能
Power (P) is the rate of energy transfer, measured in watts (W). 1 W = 1 J/s.
功率 (P) 是能量转移的速率，以瓦特 (W) 为单位，1 W = 1 J/s。
The following equations link power, current, voltage and resistance.
以下公式将功率、电流、电压和电阻联系起来。
P = I × V
P = I² R
P = V² ÷ R
Energy transferred (E) is given by E = P × t, where t is time in seconds. Energy is measured in joules (J).
转移的能量 (E) 由 E = P × t 给出，其中 t 为时间（秒），能量单位为焦耳 (J)。
In domestic electricity, energy is often measured in kilowatt-hours (kWh). 1 kWh = 3.6 × 10⁶ J.
在家庭用电中，能量常用千瓦时 (kWh) 计量。1 kWh = 3.6 × 10⁶ J。
6. Magnetism and Magnetic Fields | 磁性及磁场
A magnet has a north pole (N) and a south pole (S). Like poles repel, unlike poles attract.
磁体有北极 (N) 和南极 (S)。同名磁极相斥，异名磁极相吸。
A magnetic field is the region around a magnet where a magnetic force is experienced. Field lines go from N to S outside the magnet.
磁场是磁体周围能感受到磁力的区域。磁体外部磁感线从 N 极指向 S 极。
Magnetic materials include iron, steel, cobalt and nickel. Steel is used for permanent magnets; iron is used for temporary electromagnets because it easily magnetises and demagnetises.
磁性材料包括铁、钢、钴和镍。钢用于制造永久磁体；铁用于临时电磁铁，因其易磁化和退磁。
The Earth has a magnetic field similar to a bar magnet, with its magnetic south pole near the geographic North Pole. A compass aligns with this field.
地球有一个类似条形磁体的磁场，其磁南极位于地理北极附近。指南针根据该磁场指向。
7. Electromagnetism | 电磁铁
A current-carrying wire produces a magnetic field consisting of concentric circles around the wire. The direction can be found using the right-hand grip rule: thumb points in direction of current, fingers curl in direction of magnetic field.
载流导线周围产生环形磁场。方向可用右手螺旋定则判断：拇指指向电流方向，四指弯曲指向磁场方向。
A solenoid (coil of wire) produces a magnetic field similar to a bar magnet, with a north and south pole. The strength can be increased by increasing the current, increasing the number of turns, or inserting a soft iron core.
螺线管（线圈）产生的磁场类似条形磁体，具有北极和南极。增强磁场的方法：增大电流、增加匝数或插入软铁芯。
Electromagnets are used in relays, electric bells, circuit breakers and magnetic lifting devices.
电磁铁应用于继电器、电铃、断路
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