Electric Charge | 电荷

📚 Electric Charge | 电荷

Electric charge is a fundamental property of matter that governs how particles interact with electromagnetic fields. In your IGCSE Edexcel Physics exams, understanding charge is crucial, as it underpins topics like current electricity, magnetism, and electronics. This revision guide breaks down the key concepts into clear, exam-focused sections.

电荷是物质的一种基本属性，它决定了粒子与电磁场之间的相互作用方式。在 IGCSE Edexcel 物理考试中，理解电荷至关重要，因为它是电流、磁学和电子学等主题的基础。本复习指南将关键概念分解为清晰、紧扣考点的各个部分。

1. The Nature of Charge – Protons and Electrons | 电荷的性质 – 质子和电子

Atoms are the building blocks of matter and are composed of three main subatomic particles: protons, neutrons, and electrons. Protons reside in the nucleus and carry a positive charge. Electrons orbit the nucleus and carry an identical magnitude of negative charge. Neutrons, as their name implies, are electrically neutral. An atom becomes an ion when it gains or loses electrons, thus acquiring a net electrical charge.

原子是物质的基本组成单位，由三种主要的亚原子粒子构成：质子、中子和电子。质子位于原子核内，带正电荷。电子绕原子核运动，带等量的负电荷。中子则如其名，呈电中性。当原子获得或失去电子时，它就成为离子，从而带上净电荷。

Particle 粒子	Relative Charge 相对电荷	Relative Mass 相对质量
Proton 质子	+1	1
Neutron 中子	0	1
Electron 电子	-1	1/2000

2. The Law of Charges – Attraction and Repulsion | 电荷定律 – 同性相斥，异性相吸

The fundamental law of electrostatics is that like charges repel, and unlike charges attract. This force acts through space without direct contact. The closer the charges are, the stronger the force. The larger the magnitudes of the charges, the stronger the force. This principle explains everything from why a balloon sticks to a wall to how a lightning conductor works.

静电学的基本定律是：同性电荷相互排斥，异性电荷相互吸引。这种力可以在没有直接接触的情况下作用于空间。电荷间距离越近，作用力越强。电荷量越大，作用力也越强。这个原理解释了从气球吸附在墙上到避雷针如何工作等一切现象。

Positive and positive repel. 正电荷与正电荷相互排斥。
Negative and negative repel. 负电荷与负电荷相互排斥。
Positive and negative attract. 正电荷与负电荷相互吸引。

3. Quantisation of Charge | 电荷的量子化

Charge is quantised, meaning it exists in discrete packets. The fundamental unit of charge is the magnitude of the charge carried by a single proton or electron, denoted by e. Any object’s charge is an integer multiple of e. This means you cannot have a fraction of an electron’s worth of charge; it always comes in whole-number multiples.

电荷是量子化的，这意味着它只能以离散的包形式存在。电荷的基本单元是单个质子或电子所携带的电荷量，记为 e。任何物体的带电量都是 e 的整数倍。这意味着你不可能拥有几分之一电子电荷的量；电荷总是以整数倍的形式出现。

e = 1.6 × 10⁻¹⁹ C

Here, C stands for coulombs, the unit of charge. When solving problems, remember that a body with a deficit of electrons has a positive charge, while a body with a surplus of electrons has a negative charge.

在这里，C 代表库仑，是电荷的单位。解题时请记住，缺少电子的物体带正电，而电子过剩的物体带负电。

4. Conductors and Insulators | 导体与绝缘体

Materials differ in their ability to allow electric charge to flow. Conductors, such as metals and graphite, have free electrons that can move easily, allowing charge to flow through them. Insulators, such as glass, rubber, and plastic, have electrons that are tightly bound to their atoms, preventing the flow of charge. Semiconductors like silicon fall in between, exhibiting moderate conductivity under certain conditions.

不同材料传导电荷的能力不同。导体（如金属和石墨）具有可自由移动的电子，使电荷能够在其内部流动。绝缘体（如玻璃、橡胶和塑料）的电子被原子紧紧束缚，从而阻止电荷流动。半导体（如硅）的性能介于两者之间，在特定条件下表现出适中的导电性。

Conductors are used in wires and electrical circuits because they easily transmit charge. 导体用于导线和电路中，因为它们容易传导电荷。
Insulators are used as protective coatings on cables to prevent electric shocks. 绝缘体用作电缆的保护层，以防止触电。

5. Charging by Friction | 摩擦起电

When two different insulating materials are rubbed together, electrons can be transferred from one material to another. The material that loses electrons becomes positively charged, while the material that gains electrons becomes negatively charged. For example, rubbing a polythene rod with a cloth transfers electrons from the cloth to the rod, giving the rod a negative charge.

当两种不同的绝缘材料相互摩擦时，电子可以从一种材料转移到另一种材料。失去电子的材料带正电，而获得电子的材料带负电。例如，用布摩擦聚乙烯棒，电子会从布转移到棒上，使棒带负电。

cloth → electrons → polythene rod

Similarly, rubbing a glass rod with silk causes the glass to lose electrons and become positively charged. The material that gains electrons becomes negatively charged. A common exam question asks which material becomes positive and which becomes negative based on the electron transfer.

类似地，用丝绸摩擦玻璃棒，玻璃棒会失去电子而带正电。获得电子的材料带负电。一个常见的考题是，根据电子转移方向判断哪种材料带正电，哪种材料带负电。

6. Charging by Induction | 感应起电

Induction is the process of charging an object without direct contact. If a negatively charged rod is brought near a neutral metal sphere, electrons in the sphere are repelled to the far side, leaving the near side positively charged. If the sphere is then earthed, electrons flow away, leaving the sphere with a net positive charge even after the rod is removed.

感应起电是一种无需直接接触就能使物体带电的过程。如果将一根带负电的棒靠近一个不带电的金属球，球中的电子会被排斥到远端，使近端带正电。如果此时将球接地，电子会流走，即使移走棒后，球仍会带净正电荷。

Bring a charged object close to a conductor without touching it. 将带电物体靠近导体，但不接触。
Earth the conductor to remove or provide charges. 将导体接地以移走或提供电荷。
Remove the earthing connection, then remove the charged object. 先移除接地连接，再移走带电物体。

7. Electric Fields and Field Lines | 电场与电场线

An electric field is a region of space in which a charged object experiences an electric force. Electric field lines are used to represent this field visually. By convention, lines point from positive charges to negative charges. The closer the lines, the stronger the field. Field lines never cross each other, and they show the direction of the force on a positive test charge placed in the field.

电场是空间中带电物体能感受到电场力的一个区域。电场线用于可视化地表示这种场。按照惯例，电场线从正电荷指向负电荷。电场线越密，表示电场越强。电场线永不相交，它们表示放置在电场中的正检验电荷所受力的方向。

For a positive point charge, field lines radiate outward. 对于正点电荷，电场线向外辐射。
For a negative point charge, field lines point inward. 对于负点电荷，电场线指向内部。
Between two parallel plates with opposite charges, the field lines are parallel and evenly spaced, creating a uniform electric field. 在两块带异种电荷的平行板之间，电场线是平行且等距的，形成匀强电场。

8. Applications of Electrostatics | 静电的应用

Electrostatics has many practical applications. In electrostatic painting, paint particles are charged and attracted to the earthed metal object, creating an even coat and reducing waste. Similarly, in photocopiers, a charged drum attracts toner particles to form an image, which is then transferred to paper. Electrostatic precipitators are used in chimneys to remove smoke particles, reducing air pollution.

静电有许多实际应用。在静电喷涂中，涂料微粒带电荷后被吸引到接地的金属物体上，从而形成均匀涂层并减少浪费。类似地，在复印机中，带电的硒鼓吸附碳粉颗粒形成图像，然后将图像转印到纸上。静电除尘器用于烟囱中去除烟雾颗粒，减少空气污染。

Spray painting: paint particles are charged to attract to the object.

静电喷涂：涂料颗粒带电后被吸引到物体表面。

9. Hazards and Control of Electrostatics | 静电的危害与控制

While useful, static electricity can be dangerous. In hospitals, static discharge can affect sensitive electronics or ignite flammable anaesthetics. Lightning is a dramatic example of static discharge, where large separations of charge in clouds result in a high-voltage discharge. To control these hazards, we use earthing/grounding, anti-static sprays, and surge protectors. Aircraft and fuel trucks are earthed to prevent sparks that could ignite fuel vapours.

虽然静电很有用，但也可能带来危险。在医院，静电放电可能影响精密电子设备或引燃易燃的麻醉剂。闪电是静电放电的典型例子，云层中大量的电荷分离导致高压放电。为控制这些危害，我们使用接地、防静电喷雾和电涌保护器。飞机和油罐车必须接地以防止产生火花，避免引燃燃油蒸气。

Lightning conductors provide a safe path for charge to flow into the ground, protecting buildings. 避雷针为电荷流入地面提供了一条安全路径，从而保护建筑物。
Earthing (grounding) neutralises excess charge by allowing electrons to flow to or from the Earth. 接地通过允许电子流入或流出大地来中和多余的电荷。

10. The Gold-Leaf Electroscope | 金箔验电器

The gold-leaf electroscope is a classic instrument for detecting and testing charge. It consists of a metal cap connected to a metal rod with a gold leaf attached. When a charged object touches the cap, the charge travels down the rod, causing the leaf to repel away from the rod. This indicates the presence of charge. The angle of deflection gives a rough indication of the amount of charge.

金箔验电器是一种用于检测和测试电荷的经典仪器。它由一个金属球、一根金属杆和一片金箔组成。当带电物体接触金属球时，电荷会传导到金属杆上，导致金箔与金属杆相互排斥而张开。这表明电荷的存在。张开的程度可以粗略反映电荷量的多少。

leaf repels → charge detected

金箔张开 → 检测到电荷

This device can also be used to determine the sign of a charge by first charging it with a known charge and observing whether the leaf rises or falls when a test charge is brought near.

该仪器还可用于判断电荷的正负：先用已知电荷给验电器充电，然后观察当测试电荷靠近时金箔是张开更大还是闭合减小。

Published by TutorHao | Physics Revision Series | aleveler.com

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Electric Charge | 电荷