📚 Electric Charge: Definition, Charge Carriers and Electric Fields | 电荷：定义、电荷载体与电场
Electric charge is one of the most fundamental properties of matter, and it explains a huge range of phenomena - from the lightning that flashes inside a thundercloud to the tiny current flowing through a torch bulb. In the IGCSE Edexcel Physics specification, charge is the starting point for understanding current, static electricity, electric fields and even the structure of the atom itself. This article covers the nature of charge, the atomic structure behind charge carriers, conductors and insulators, the three ways of charging an object, electric fields, and the quantitative link between charge and current.
电荷是物质最基本的一种属性，它可以解释从雷雨云中的闪电到手电筒灯泡里微小电流等大量现象。在 IGCSE 爱德思物理大纲中，电荷是理解电流、静电、电场乃至原子结构本身的起点。本文涵盖电荷的本质、电荷载体背后的原子结构、导体与绝缘体、使物体带电的三种方式、电场，以及电荷与电流之间的定量关系。
1. What is Electric Charge? | 什么是电荷？
Electric charge is a fundamental property of particles that makes them experience a force when they are placed in an electric field. Charge is measured in coulombs (C), a unit named after the French physicist Charles-Augustin de Coulomb, and it is given the symbol Q. There are only two types of charge in nature: positive charge and negative charge.
电荷是粒子的一种基本属性，它使粒子处于电场中时受到力的作用。电荷的单位是库仑（C），这一单位以法国物理学家查尔斯-奥古斯丁·德·库仑命名，符号为 Q。自然界中只有两种电荷：正电荷和负电荷。
Charged objects interact with one another in a very simple way: two objects carrying the same type of charge repel each other, while two objects carrying opposite types of charge attract each other. In an atom, protons carry positive charge, electrons carry negative charge, and neutrons carry no charge at all.
带电物体之间的相互作用规律非常简单：带同种电荷的两个物体相互排斥，而带异种电荷的两个物体相互吸引。在原子中，质子带正电，电子带负电，中子则完全不带电。
me magnitude of charge but with a positive sign, that is +1.6 × 10⁻¹⁹ C. A neutral object contains equal numbers of protons and electrons, so the total positive charge cancels the total negative charge and the net charge is zero.
单个电子所带电荷的大小为 1.6 × 10⁻¹⁹ C，这是能够独立存在的最小电荷量。质子所带电荷的大小与电子完全相同，但符号为正，即 +1.6 × 10⁻¹⁹ C。中性物体含有数量相等的质子和电子，因此正电荷总量与负电荷总量相互抵消，净电荷为零。
e = 1.6 × 10⁻¹⁹ C (elementary charge, symbol e)
Remember that a charged object also attracts a small neutral object, such as a charged rod attracting tiny scraps of paper. This attraction happens because the charged rod polarises the neutral scraps, pulling opposite charges closer and pushing like charges away. It is a common exam trap to think that attraction always means the two objects must have opposite charges.
请记住，带电物体也会吸引小型的中性物体，例如带电的棒吸引小纸屑。这种吸引之所以发生，是因为带电棒使中性纸屑发生极化，把异种电荷拉近、把同种电荷推远。认为"相互吸引就一定意味着两个物体带异种电荷"是一个常见的考试陷阱。
2. Atomic Structure and Charge Carriers | 原子结构与电荷载体
All matter consists of atoms. Each atom has a tiny, dense nucleus containing protons (positive) and neutrons (neutral), surrounded by electrons (negative) that occupy energy levels or shells around the nucleus. Nearly all of the mass of an atom is concentrated in the nucleus, because a proton is about 1836 times more massive than an electron.
所有物质都由原子组成。每个原子都有一个极小、极密的原子核，其中包含质子（带正电）和中子（不带电），核外有占据能级或壳层的电子（带负电）绕核运动。原子几乎全部的质量都集中在原子核内，因为一个质子的质量大约是电子的 1836 倍。
Protons are fixed inside the nucleus and cannot move from one atom to another in ordinary physical and chemical processes. Electrons, especially the outer ones, are relatively free to move, so it is electrons that are responsible for transferring charge from one place to another. This is why we say that the electron is the mobile negative charge carrier in most situations.
在普通的物理和化学过程中，质子被固定在原子核内，不能从一个原子移动到另一个原子；而电子，特别是外层电子，相对自由，因此负责把电荷从一个地方转移到另一个地方。这就是为什么我们说，在大多数情况下电子是可移动的负电荷载体。
The identity of the charge carriers depends on the material:
电荷载体的种类取决于材料：
- In solid metal conductors, free (delocalised) electrons drift through the metal lattice and carry the charge. In solid conductors, free electrons are the main charge carriers.
- 在固态金属导体中，自由（离域）电子在金属晶格中漂移并携带电荷。在固态导体中，自由电子是主要的电荷载体。
- In liquids such as salt solution or molten ionic compounds, positive and negative ions move towards the electrodes and carry the charge.
- 在盐水或熔融离子化合物等液体中，正离子和负离子分别向电极移动并携带电荷。
- In gases such as neon in a discharge tube, ions and electrons produced by ionisation both act as charge carriers.
- 在放电管中的氖气等气体里，电离产生的离子和电子都可以充当电荷载体。
In each case, the material must contain particles that are free to move, which is exactly what separates a conductor from an insulator.
在每一种情况下，材料中都必须含有可以自由运动的粒子，而这正是区分导体与绝缘体的关键。
3. Positive and Negative Charges | 正电荷与负电荷
There are two types of charge, called positive charge and negative charge. Objects carrying the same type of charge repel one another, while objects carrying different types of charge attract one another. This single rule explains almost all electrostatic behaviour you will meet in the IGCSE course.
电荷有两种类型，称为正电荷和负电荷。带有同种电荷的物体相互排斥，而带有异种电荷的物体相互吸引。这一条简单的规则几乎可以解释你在 IGCSE 课程中遇到的绝大多数静电现象。
Whether an object becomes positive or negative depends entirely on electrons. When an object gains electrons it becomes negatively charged, because it now has more electrons than protons. When an object loses electrons it becomes positively charged, because the number of protons then exceeds the number of electrons. Neutrons are never transferred, and in solid materials protons never move.
一个物体带正电还是带负电，完全取决于电子。物体获得电子时带负电，因为此时它的电子数多于质子数；物体失去电子时带正电，因为此时质子数多于电子数。中子永远不会被转移，而在固体材料中质子也永远不移动。
An important sign convention follows from this. Because the electron itself carries a negative charge, the statement "an object gains electrons" and the statement "an object becomes negatively charged" mean exactly the same thing. Always check the direction of electron transfer before writing your answer in an exam.
由此可以得出一个重要的符号约定。由于电子本身带负电，"物体获得电子"和"物体带负电"这两句话的含义完全相同。考试作答前，务必先确认电子转移的方向。
A charged object can also attract a neutral object, as described in Section 1, but two charged objects can only repel each other if they carry the same type of charge. Repulsion between two charged objects is therefore the only reliable test that they both carry the same charge type.
如第 1 节所述，带电物体也能吸引中性物体，但两个带电物体只有在带同种电荷时才会相互排斥。因此，两个带电物体之间的排斥是判断它们带同种电荷的唯一可靠依据。
4. Quantisation and Conservation of Charge | 电荷的量子化与守恒
In other words, charge comes in discrete packets, and you can never have half an electron's worth of charge. This property is called the quantisation of charge.
任何电荷的大小总是基本电荷 e = 1.6 × 10⁻¹⁹ C 的整数倍。换句话说，电荷以离散的"份额"存在，你永远不可能有半个电子的电荷量。这一性质称为电荷的量子化。
Q = n × e = n × 1.6 × 10⁻¹⁹ C
This discrete nature is very important at the atomic scale, where we deal with single electrons and ions. However, for most macroscopic phenomena - such as the charge on a rubbed polythene rod, which may involve billions of electrons - the individual steps are far too small to notice, so we treat charge as if it were continuous.
这种离散性在原子尺度上非常重要，因为我们处理的正是单个电子和离子。然而，对于大多数宏观现象——例如因摩擦而带电的聚乙烯棒，其电荷可能涉及数十亿个电子——单个台阶实在太小而无法察觉，因此我们就把电荷当作连续量来处理。
Charge is also conserved. Charge can never be created or destroyed; it can only be transferred from one object to another. When a polythene rod is rubbed with a cloth, the rod gains electrons and becomes negative, while the cloth loses exactly the same number of electrons and becomes positive by an equal amount. The total charge of the rod-cloth system stays at zero.
电荷还是守恒的。电荷既不能被创造，也不能被消灭，只能从一个物体转移到另一个物体。当聚乙烯棒与布摩擦时，棒获得电子而带负电，布则失去同样数量的电子，并因此带等量的正电。棒与布这一系统的总电荷仍为零。
Conservation of charge is a universal law. It applies in chemical reactions, in nuclear decay, and even when a particle and its antiparticle annihilate - the net charge before and after the event is always identical.
电荷守恒是一条普适定律。它适用于化学反应、核衰变，甚至适用于粒子与反粒子湮灭的情形——事件前后的净电荷始终相同。
5. Conductors and Insulators | 导体与绝缘体
Materials are divided into conductors and insulators according to how easily charge can move through them. In a conductor, some electrons are free to move throughout the material, so charge can flow easily from one end to the other. In an insulator, all the electrons are tightly bound to their own atoms, so charge cannot flow through the material.
材料根据电荷在其中移动的难易程度被分为导体与绝缘体。在导体中，部分电子可以在整个材料内自由移动，因此电荷可以轻易地从一端流向另一端。在绝缘体中，所有电子都被紧紧地束缚在自己的原子上，因此电荷无法在材料中流动。
| Feature | 特征 | Conductor | 导体 | Insulator | 绝缘体 |
| Free electrons | 自由电子 | Many free (delocalised) electrons | 有大量自由（离域）电子 | Electrons tightly bound to atoms | 电子被紧紧束缚在原子中 |
| Charge flow | 电荷流动 | Charge flows easily | 电荷容易流动 | Charge cannot flow through the bulk | 电荷无法在材料内部流动 |
| Can be charged by friction? | 可通过摩擦带电？ | Difficult - charge leaks away, needs earthing of the rest of the circuit | 较难——电荷会泄漏，需将其他部分接地 | Yes - charge stays where it is deposited | 可以——电荷停留在沉积处 |
| Examples | 例子 | Copper, aluminium, silver, graphite, salt solution | 铜、铝、银、石墨、盐溶液 | Polythene, Perspex, glass, rubber, dry air, plastic | 聚乙烯、有机玻璃、玻璃、橡胶、干燥空气、塑料 |
It is worth noting that insulators are actually excellent for demonstrating static electricity precisely because the charge they gain from friction cannot escape. A metal rod rubbed with a cloth will not stay charged for long, because the charge flows away through the rod and through your hand to earth.
值得一提的是，绝缘体恰恰因为摩擦所获得的电荷无法逃逸，所以非常适合用来演示静电现象。用布摩擦金属棒则无法长时间带电，因为电荷会通过金属棒、再经过你的手流向大地。
6. Methods of Charging an Object | 使物体带电的方法
There are three ways of charging an object that you need to know: charging by friction, charging by contact (conduction), and charging by induction. All three work by moving electrons, never protons.
你需要掌握三种使物体带电的方法：摩擦起电、接触（传导）起电和感应起电。这三种方法都是通过移动电子实现的，而不是移动质子。
Charging by friction happens when two insulators are rubbed together. Electrons are transferred from the material that holds them less tightly to the material that holds them more tightly. The two objects end up with equal and opposite charges. A polythene rod rubbed with a dry cloth becomes negative; a Perspex rod rubbed with the same cloth becomes positive.
当两种绝缘体相互摩擦时就会发生摩擦起电。电子会从束缚较弱的材料转移到束缚较强的材料上。两个物体最终带上等量异种电荷。用干布摩擦的聚乙烯棒带负电；用同一块布摩擦的有机玻璃棒则带正电。
Charging by contact, also called charging by conduction, happens when a charged conductor touches an uncharged conductor. Electrons flow from the object with the higher electron concentration to the other one, so both objects end up with the same type of charge as the original charged object.
接触起电，也叫传导起电，发生在带电导体与不带电导体接触时。电子会从电子浓度较高的一方流向另一方，因此两个物体最终都带上与原来带电物体同种的电荷。
Charging by induction happens without any contact at all. A charged rod brought near a neutral conductor pushes or pulls electrons within the conductor, causing a temporary separation of charge. If the conductor is earthed while the rod is still nearby and the earth connection is removed before the rod is taken away, the conductor is left with a permanent charge of the opposite sign to the rod.
感应起电完全不需要接触。把带电棒靠近中性导体时，棒会排斥或吸引导体内部的电子，使导体内的电荷暂时分离。如果在带电棒仍然靠近时把导体接地，并在移开带电棒之前先断开接地线，那么导体就会留下与带电棒相反的永久电荷。
Charging by heating or by the photoelectric effect also transfers electrons, but these are outside the main IGCSE specification and are usually only mentioned as extensions.
加热起电或光电效应也会转移电子，但这些内容超出了 IGCSE 主体大纲，通常只作为拓展提及。
7. Static Electricity in Everyday Life | 生活中的静电
Static electricity is charge that has built up on an insulator and cannot flow away. It is useful in some technologies and dangerous in others, and exam questions often ask you to identify the mechanism behind a real-life example.
静电是积累在绝缘体上、无法流走的电荷。它在某些技术中十分有用，在另一些场合却很危险，考试题目常常要求你指出某个生活实例背后的原理。
d becomes highly charged. When the electric field between the cloud and the ground becomes large enough (roughly 3 × 10⁶ V m⁻¹), air stops being an insulator and breaks down. A giant spark - lightning - discharges the cloud, and the rapid heating of the air along the path produces thunder.
闪电是最引人注目的例子。雷雨云中的冰粒与水滴之间的摩擦转移了电子，使云层带上大量电荷。当云层与地面之间的电场强到足以（约 3 × 10⁶ V m⁻¹）使空气击穿时，空气就不再是绝缘体。一个巨大的火花——闪电——使云层放电，沿途空气被迅速加热，从而产生雷声。
Other everyday examples include the small shock you feel when you touch a metal door handle after walking on a synthetic carpet, and the spark that can occur when a car or aircraft is refuelled. For this reason, fuel tankers have a metal earthing chain that drags on the road, and aircraft are earthed before refuelling, so that any charge flows safely to the ground instead of producing a spark near the fuel vapour.
其他日常例子包括：走过化纤地毯后触碰金属门把手时感到的小电击，以及汽车或飞机加油时可能出现的火花。因此，油罐车会拖一条金属接地链与路面接触，飞机在加油前也要接地，以便任何电荷都能安全地流入大地，而不是在燃油蒸气附近产生火花。
Static electricity is also put to good use. Electrostatic dust precipitators charge smoke particles and collect them on oppositely charged plates, reducing pollution from power stations. Electrostatic paint spraying charges paint droplets so that they are attracted to the car body, which wastes much less paint than ordinary spraying.
静电也有很好的用途。静电除尘器使烟尘颗粒带电，再让它们吸附到带相反电荷的极板上，从而减少发电厂的污染。静电喷漆使油漆液滴带电，从而被吸引到车身表面，比普通喷涂浪费的油漆少得多。
8. Electric Fields | 电场
An electric field is a region of space in which a charged particle experiences an electric force. Every charged object is surrounded by its own electric field, and the field is what allows a charged object to exert a force on another charged object without the two ever touching.
电场是空间中带电粒子会受到电力的区域。每个带电物体周围都存在自己的电场，正是电场使得带电物体无需接触就能对另一个带电物体施加力的作用。
The strength of an electric field at a point is defined as the force per unit positive charge placed at that point. The unit of electric field strength is the newton per coulomb (N C⁻¹), which is equivalent to the volt per metre (V m⁻¹).
某一点的电场强度定义为放在该点的单位正电荷所受到的力。电场强度的单位是牛顿每库仑（N C⁻¹），它与伏特每米（V m⁻¹）等价。
E = F ÷ Q (electric field strength = force ÷ charge)
Electric field lines are drawn to show the direction and relative strength of the field. By convention, field lines point away from positive charge and towards negative charge, so they always run from positive to negative. Lines that are close together indicate a strong field, and lines that are widely spaced indicate a weak field. Field lines never cross one another.
电场线用于表示电场的方向和相对强弱。按约定，电场线从正电荷出发、指向负电荷，因此总是由正指向负。电场线越密表示电场越强，越疏表示电场越弱。电场线永远不会相交。
Around an isolated point charge the field is radial. Between two parallel charged plates the field is uniform: the field lines are parallel, equally spaced straight lines running from the positive plate to the negative plate. The uniform field between parallel plates is the standard model used in IGCSE questions, and it is also the situation found inside a cathode ray tube or an inkjet printer nozzle.
在孤立点电荷周围，电场是辐射状的。在两块平行的带电板之间，电场是匀强电场：电场线是平行、等间距的直线，从正极板指向负极板。平行板之间的匀强电场是 IGCSE 题目中使用的标准模型，也是阴极射线管或喷墨打印机喷嘴内部的情形。
A sharp point concentrates charge and therefore creates a very strong electric field around itself. This is why lightning conductors have sharp spikes, and why spark plugs and Van de Graaff generators are designed with pointed electrodes.
尖端会聚集电荷，因此其周围会形成非常强的电场。这就是避雷针带有尖刺的原因，也是火花塞和范德格拉夫起电机采用尖端电极的原因。
9. Charge and Current | 电荷与电流
When charge flows, we call it an electric current. Current is defined as the rate of flow of charge, and the relationship between charge, current and time is one of the most frequently examined equations in the whole specification.
当电荷流动时，我们称之为电流。电流定义为电荷流动的速率，而电荷、电流与时间之间的关系是整个大纲中最常考的公式之一。
Q = I × t (charge = current × time)
oulomb per second. One coulomb is the charge carried by approximately 6.25 × 10¹⁸ electrons.
在该式中，Q 是电荷量，单位为库仑（C）；I 是电流，单位为安培（A）；t 是时间，单位为秒（s）。因此，1 安培等于每秒 1 库仑。1 库仑约等于 6.25 × 10¹⁸ 个电子所携带的电荷量。
| Quantity | 物理量 | Symbol | 符号 | Unit | 单位 |
| Charge | 电荷量 | Q | coulomb (C) | 库仑（C） |
| Current | 电流 | I | style="border:1px solid #ccc;padding:8
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