📚 Static Electricity and Charge Mark Scheme | 静电与电荷评分标准
This article covers the key ideas and mark scheme points for KS3 CIE static electricity and charge. It explains how objects become charged, how charges interact, and how examiners award marks for explanations.
本文涵盖 KS3 CIE 静电与电荷的核心概念和评分标准要点，解释物体如何带电、电荷如何相互作用，以及阅卷人如何给解释性答案打分。
1. Charge Basics | 电荷基础
All matter is made of atoms. Atoms contain protons, neutrons and electrons. Protons have a positive charge, electrons have a negative charge, and neutrons have no charge.
所有物质都由原子组成。原子包含质子、中子和电子。质子带正电荷，电子带负电荷，中子不带电。
An object is neutral when it has equal numbers of protons and electrons. An object becomes charged only when electrons are transferred from one object to another.
当质子数和电子数相等时，物体呈电中性。物体带电仅发生在电子从一个物体转移到另一个物体时。
In the mark scheme, a key point is that positive charge is caused by losing electrons, not by gaining protons. Protons remain fixed in the nucleus.
评分标准中的关键点是：带正电是因为失去电子，而不是获得质子。质子固定在原子核内。
2. Charging by Friction | 摩擦起电
Rubbing two insulators together transfers electrons from one material to the other. The material that gains electrons becomes negatively charged; the material that loses electrons becomes positively charged.
两种绝缘体相互摩擦会使电子从一种材料转移到另一种材料。获得电子的材料带负电；失去电子的材料带正电。
Mark schemes often require you to name a specific example, such as a polythene rod rubbed with a cloth. The polythene rod becomes negatively charged because electrons move from the cloth to the rod.
评分标准常要求举出具体例子，例如用布摩擦聚乙烯棒。聚乙烯棒带负电，因为电子从布转移到棒上。
When an acetate rod is rubbed with a cloth, the acetate rod becomes positively charged because it loses electrons to the cloth.
用布摩擦醋酸纤维棒时，醋酸纤维棒带正电，因为它将电子转移给了布。
3. Attraction and Repulsion | 吸引与排斥
Objects with like charges repel each other. Objects with opposite charges attract each other.
带同种电荷的物体相互排斥。带异种电荷的物体相互吸引。
A charged object can also attract a neutral object. The charged object induces a separation of charge on the surface of the neutral object.
带电物体也能吸引中性物体。带电物体使中性物体表面产生电荷分离，这种现象称为静电感应。
In an exam answer, avoid saying ‘charges attract’ without saying ‘opposite charges’. Examiners expect the exact phrase ‘opposite charges attract’ or ‘like charges repel’.
在考试答案中，不要只写“电荷吸引”而不说明“异种电荷”。阅卷人要求准确表述“异种电荷相互吸引”或“同种电荷相互排斥”。
4. Conductors and Insulators | 导体与绝缘体
Conductors, such as metals, allow electrons to move through them. Insulators, such as plastic and glass, do not allow electrons to move easily.
导体（如金属）允许电子在其中移动。绝缘体（如塑料和玻璃）不允许电子轻易移动。
Static charge builds up on insulators because the charge cannot flow away. A conductor must be insulated from the ground to hold a static charge.
静电在绝缘体上积累，因为电荷无法流走。导体必须与地面绝缘才能保持静电。
Mark schemes often award marks for saying that metals contain free electrons, whereas insulators do not have free electrons available for conduction.
评分标准通常给分点包括：金属含有自由电子，而绝缘体没有可导电的自由电子。
5. Electric Fields | 电场
A charged object creates an electric field around it. The field is strongest near the charged object and becomes weaker further away.
带电物体周围产生电场。电场在带电物体附近最强，离得越远越弱。
Electric field lines show the direction of force on a small positive test charge. Field lines point away from positive charges and towards negative charges.
电场线表示小正试探电荷所受力的方向。电场线从正电荷出发指向负电荷。
KS3 mark schemes usually accept a simple description: an electric field is a region where a force acts on another charged object without touching it.
KS3 评分标准通常接受简单描述：电场是一种区域，其中带电物体不接触也会受到力的作用。
6. Sparks and Earthing | 火花与接地
If the charge on an object becomes large enough, electrons can jump across a gap to a nearby conductor. This produces a spark.
如果物体上的电荷足够大，电子会跨越间隙跳到附近导体上，从而产生火花。
Earthing means connecting a charged object to the ground with a conductor. Electrons flow to or from the earth to discharge the object.
接地是指用导体将带电物体与大地相连。电子流向或流自大地，使物体放电。
Mark schemes award marks for stating that earthing removes excess charge. A spark is evidence that charge is moving through the air.
评分标准给分点包括：接地能移除多余电荷。火花表明电荷正在空气中移动。
7. Common Mark Scheme Points | 常见评分点
Use precise language. Say ‘electrons are transferred’, not ‘charge is transferred’ when explaining how an insulator becomes charged.
使用准确语言。解释绝缘体如何带电时，说“电子转移”，而不是“电荷转移”。
If an object gains electrons, it becomes negatively charged. If an object loses electrons, it becomes positively charged. The total charge before and after remains conserved.
如果物体获得电子，它带负电。如果物体失去电子，它带正电。摩擦前后总电荷守恒。
When explaining attraction between a charged and a neutral object, say the charged object induces charge separation, then opposite charges attract.
解释带电物体与中性物体吸引时，说明带电物体引起电荷分离，然后异种电荷相互吸引。
For discharge, say electrons move through the conductor to earth. For a spark, say electrons jump through air because the electric field is strong enough to ionise the air.
对于放电，说明电子通过导体流向大地。对于火花，说明电子穿过空气，因为电场强到足以使空气电离。
8. Common Mistakes | 常见错误
Many students say ‘protons move to make an object positive’. This is wrong because protons are fixed in the nucleus. Only electrons move.
许多学生说“质子移动使物体带正电”。这是错误的，因为质子固定在原子核中。只有电子能移动。
Saying ‘the object gains positive charge’ without explaining the loss of electrons may lose a mark. You should link positive charge to a loss of electrons.
说“物体获得正电荷”而不说明失去电子，可能会丢分。应将正电荷与失去电子联系起来。
Confusing attraction with repulsion is another common error. Remember: opposite charges attract, like charges repel.
混淆吸引和排斥是另一个常见错误。记住：异种电荷相吸，同种电荷相斥。
Some students say insulators do not allow any charge to move. More accurate is: insulators do not allow electrons to move freely through them.
有些学生说绝缘体不允许任何电荷移动。更准确的说法是：绝缘体不允许电子在其中自由移动。
9. Worked Examples | 例题解析
Example 1: A polythene rod is rubbed with a cloth and then brought near a neutral piece of paper. State why the paper is attracted.
例 1：用布摩擦聚乙烯棒，然后靠近中性纸片。说明纸片为何被吸引。
Model answer: The rod becomes negatively charged because electrons move from the cloth to the rod. The negative rod repels electrons on the paper surface, making the near side positive. Opposite charges attract, so the paper is attracted.
参考答案：聚乙烯棒因电子从布转移到棒而带负电。负电棒排斥纸片表面的电子，使近端带正电。异种电荷相互吸引，因此纸片被吸引。
Example 2: Explain how a charged person becomes discharged when touching a metal door handle.
例 2：解释带电的人接触金属门把手时如何放电。
Model answer: Excess electrons on the person flow through the metal handle to the earth because the handle is a conductor. This removes the excess charge, so the person becomes neutral.
参考答案：人身上多余的电子通过金属把手流向大地，因为把手是导体。这移除了多余电荷，人恢复电中性。
Example 3: Explain why a charged balloon sticks to a wall.
例 3：解释为什么带电气球会粘在墙上。
Model answer: The charged balloon induces charge separation on the wall surface. The opposite charge is pulled towards the balloon, causing attraction. The balloon sticks because opposite charges attract.
参考答案：带电气球使墙面产生电荷分离。异种电荷被拉向气球，产生吸引力。气球因异种电荷相吸而粘住。
10. Exam Technique | 考试技巧
Always read the number of marks. A one-mark question usually needs one point; a two-mark question needs an explanation with a cause and an effect.
始终注意分值。1 分题通常只需一个要点；2 分题需要包含原因和结果的解释。
Use key words such as electron, transfer, repel, attract, conductor, insulator, earth, discharge. These are often on the mark scheme.
使用关键词，如电子、转移、排斥、吸引、导体、绝缘体、接地、放电。这些通常出现在评分标准中。
If the question says ‘explain’, do not just state the result. Give a reason using electron movement. For example, ‘The rod becomes negative because it gains electrons.’
如果题目要求“解释”，不要只陈述结果。要用电子移动给出原因。例如，“棒带负电是因为它获得了电子。”
Check your spelling of science words. In CIE mark schemes, a misspelt key term can sometimes cost clarity marks if the meaning is unclear.
检查科学词汇的拼写。在 CIE 评分标准中，如果关键术语拼写错误导致意思不清，可能失去清晰度分数。
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