📚 Static Electricity and Charge Questions | 静电与电荷问题
This revision guide covers the essential KS3 CIE questions on static electricity and electric charge. You will learn how charge builds up, how insulators and conductors behave, and how to explain common static effects using the idea of electron transfer. The examples and answers will help you prepare for Checkpoint tests and end-of-topic assessments.
本复习指南涵盖 KS3 CIE 静电与电荷的核心问题。你将学习电荷如何积累、绝缘体与导体的表现，以及如何用电子转移解释常见静电现象。例题和答案将帮助你为 Checkpoint 测试和章节评估做好准备。
1. What is electric charge? | 什么是电荷
Electric charge is a basic property of particles. There are two types of charge: positive and negative. Protons carry positive charge, electrons carry negative charge, and neutrons have no charge.
电荷是粒子的基本性质。电荷有两种：正电荷和负电荷。质子带正电，电子带负电，中子不带电。
The unit of electric charge is the coulomb, symbol C. A single electron carries a tiny charge of about 1.6 × 10⁻¹⁹ C.
电荷的单位是库仑，符号为 C。一个电子所带的电荷极小，约为 1.6 × 10⁻¹⁹ C。
Charge of one electron e = 1.6 × 10⁻¹⁹ C
An atom is normally neutral because it contains equal numbers of protons and electrons.
原子通常呈电中性，因为它含有相同数量的质子和电子。
2. How charging by friction works | 摩擦起电的原理
When two different insulating materials are rubbed together, electrons can be transferred from one surface to the other.
当两种不同的绝缘材料相互摩擦时，电子会从一个表面转移到另一个表面。
The material that gains electrons becomes negatively charged. The material that loses electrons becomes positively charged.
得到电子的材料带负电，失去电子的材料带正电。
For example, a polythene rod rubbed with wool gains electrons from the wool, so the rod becomes negative and the wool becomes positive.
例如，用羊毛摩擦聚乙烯棒时，聚乙烯棒从羊毛获得电子，因此棒带负电，羊毛带正电。
Only electrons move. Positive protons do not move because they are held tightly inside the nucleus.
只有电子会移动。正质子不会移动，因为它们被紧紧束缚在原子核内。
3. Conservation of charge | 电荷守恒
Electric charge cannot be created or destroyed. It can only be transferred from one object to another.
电荷不能被创造或消灭，只能从一个物体转移到另一个物体。
When a rod and cloth are rubbed together, the total charge before rubbing is zero. The total charge after rubbing is still zero, because equal positive and negative charges are produced.
当棒和布摩擦时，摩擦前的总电荷为零。摩擦后的总电荷仍然为零，因为产生了等量的正电荷和负电荷。
Total charge before = Total charge after
This idea is called the conservation of electric charge.
这一观点称为电荷守恒。
4. Conductors and insulators | 导体与绝缘体
Materials can be divided into electrical conductors and electrical insulators. Conductors allow electrons to flow through them easily. Insulators do not.
材料可分为导体和绝缘体。导体允许电子轻易通过，绝缘体则不允许。
Metals such as copper and aluminium are good conductors because they contain free electrons that can move.
铜和铝等金属是良导体，因为它们含有可以移动的自由电子。
Plastics, rubber, glass and dry wood are insulators. Their electrons are tightly bound to atoms, so charge cannot flow through them.
塑料、橡胶、玻璃和干木材是绝缘体。它们的电子被原子束缚得很紧，因此电荷不能通过。
Static charge builds up most easily on insulators because the charge cannot move away.
静电最容易在绝缘体上积累，因为电荷无法流走。
A charged conductor can be discharged by touching it with a conductor connected to the Earth. This is called earthing.
带电的导体可以通过用连接到地球的导体接触来放电。这称为接地。
5. Attraction and repulsion | 吸引与排斥
There is a simple rule for electric forces: like charges repel each other, and unlike charges attract each other.
电荷间的简单规则是：同种电荷互相排斥，异种电荷互相吸引。
Two positively charged objects push each other apart. Two negatively charged objects also push each other apart.
两个带正电的物体会互相推开。两个带负电的物体也会互相推开。
A positively charged object and a negatively charged object pull towards each other.
带正电的物体和带负电的物体会互相吸引。
A charged object can also attract a neutral object. This happens because the charged object induces a separation of charge on the neutral object.
带电物体也可以吸引中性物体。这是因为带电物体使中性物体上的电荷发生分离。
This explains why a charged balloon can stick to an uncharged wall or attract small pieces of paper.
这解释了为什么带电的气球能贴在未带电的墙上，或吸引小纸片。
6. Explaining common static effects | 常见静电现象解释
Hair standing on end: when you comb dry hair with a plastic comb, electrons move. Each hair gains the same charge, so the hairs repel each other and stand up.
头发竖立：用塑料梳子梳理干燥头发时，电子发生转移。每根头发带上同种电荷，因此头发相互排斥并竖立。
Balloon sticking to a wall: rubbing a balloon on a jumper transfers charge. The charged balloon induces an opposite charge on the wall surface, so they attract.
气球粘在墙上：在毛衣上摩擦气球会转移电荷。带电的气球使墙壁表面感应出相反电荷，因此相互吸引。
A spark from a door handle: charge builds up on your body after walking on a carpet. When your hand touches a metal handle, the charge jumps across the small air gap, producing a spark.
门把手产生电火花：在地毯上行走后，身体会积累电荷。当手接触金属把手时，电荷跳过微小的空气间隙，产生火花。
Lightning: clouds become charged by friction as ice particles move. A huge spark can jump between clouds and the ground.
闪电：云层中的冰粒运动通过摩擦带电。巨大的电火花可以在云层和地面之间跳跃。
7. Electric fields around charges | 电荷周围的电场
A charged object creates an electric field around itself. The field is a region where other charges feel a force.
带电物体周围会产生电场。电场是其他电荷会受到力的作用的区域。
The direction of an electric field is defined as the direction of the force on a small positive test charge.
电场方向定义为作用在小的正检验电荷上的力的方向。
Field lines point away from positive charges and towards negative charges.
电场线从正电荷出发，指向负电荷。
The closer the field lines, the stronger the electric field.
电场线越密集，电场越强。
You can see the effect of an electric field by bringing a charged rod close to a thin stream of water. The water bends towards the rod.
将带电棒靠近细水流，可以看到水向棒弯曲，这就是电场的作用。
8. Static electricity in everyday life | 生活中的静电
Useful applications include electrostatic paint spraying, photocopiers and laser printers, and electrostatic precipitators that clean smoke.
静电的有利应用包括静电喷涂、复印机和激光打印机，以及净化烟雾的静电除尘器。
In electrostatic paint spraying, the paint droplets and the object are given opposite charges. The paint is attracted evenly to the surface, reducing waste.
在静电喷涂中，油漆液滴和物体带相反电荷。油漆被均匀吸引到表面，减少浪费。
In a photocopier, a charged drum attracts toner particles to form an image, which is then transferred to paper.
在复印机中，带电的感光鼓吸引墨粉颗粒形成图像，然后转印到纸上。
Static electricity is also used in air purifiers to remove dust and pollen particles from the air.
静电还用于空气净化器中，以去除空气中的灰尘和花粉颗粒。
9. Dangers and safety | 静电危害与安全
Static electricity can be dangerous when it causes sparks near flammable gases or liquids. A spark at a petrol station could start a fire.
静电在易燃气体或液体附近产生火花时可能很危险。加油站的火花可能引发火灾。
Moving fuel through pipes can build up static charge. Tankers and aircraft are earthed to prevent dangerous sparks.
燃料在管道中流动会积累静电。油罐车和飞机会接地，以防止危险火花。
Lightning is a large natural static discharge. Lightning conductors on tall buildings safely carry the charge to the ground.
闪电是一种大规模的自然静电放电。高建筑上的避雷针将电荷安全导入地面。
In factories, workers may wear anti-static shoes and wrist straps to prevent charge building up on electronic components.
在工厂中，工人可能穿戴防静电鞋和腕带，以防止电子元件上积累电荷。
10. Exam-style questions and answers | 考试题型与答案
Q1: A polythene rod is rubbed with a woollen cloth. State which particles move and explain why the rod becomes negatively charged.
问题1：用羊毛布摩擦聚乙烯棒。说明哪种粒子移动，并解释为什么棒带负电。
Answer: Electrons move from the wool to the polythene rod. The rod gains electrons, and since electrons are negative, the rod becomes negatively charged. The wool loses electrons and becomes positively charged.
答案：电子从羊毛转移到聚乙烯棒上。棒得到电子，因为电子带负电，所以棒带负电。羊毛失去电子而带正电。
Q2: Explain why a charged balloon sticks to a wall.
问题2：解释为什么带电的气球会粘在墙上。
Answer: The charged balloon creates an electric field. It induces the opposite charge on the surface of the wall. The opposite charges attract, so the balloon sticks.
答案：带电气球产生电场。它使墙壁表面感应出相反电荷。异种电荷相互吸引，所以气球粘在墙上。
Q3: Describe one danger of static electricity and one way to reduce the risk.
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