📚 Current and Voltage: KS3 CIE Mark Scheme Guide | 电流与电压：KS3 CIE 评分方案指南
This revision guide explains how marks are typically awarded for KS3 CIE questions on current and voltage. It covers the key definitions, circuit rules, measuring techniques and the exact wording that examiners expect in mark schemes. Use this guide to check your answers against the style and precision required by mark schemes.
本复习指南解释 KS3 CIE 关于电流和电压的题目通常如何给分。它涵盖关键定义、电路规律、测量方法以及评分方案中阅卷老师期望的精确表述。使用本指南来检查你的答案是否符合评分方案要求的风格和准确性。
1. Current: Definition and Unit | 电流：定义与单位
Electric current is the rate of flow of electric charge around a circuit. In a metal wire, the moving charges are electrons.
电流是电荷在电路中流动的速率。在金属导线中，移动的电荷是电子。
The unit of current is the ampere, usually shortened to amp, with the symbol A. In equations, current is represented by the letter I.
电流的单位是安培，通常简称为安，符号为 A。在公式中，电流用字母 I 表示。
Mark schemes often award one mark for stating that current is measured in amperes and one mark for identifying that electrons are the charge carriers in a metal.
评分方案通常给一分用于说明电流以安培为单位，再给一分用于指出电子是金属中的电荷载体。
= Q ÷ t, where Q is charge in coulombs, I is current in amperes and t is time in seconds.
电荷、电流和时间的关系为 I = Q ÷ t，其中 Q 是电荷（单位库仑），I 是电流（单位安培），t 是时间（单位秒）。
For KS3 mark schemes, a simple definition such as 'current is the flow of charge' often gains full marks, but adding 'per second' or 'rate of flow' can make the answer more precise.
对于 KS3 评分方案，像“电流是电荷的流动”这样的简单定义通常就能得满分，但加上“每秒”或“流动速率”会让答案更精确。
2. Voltage: Definition and Unit | 电压：定义与单位
Voltage, also called potential difference, measures the energy transferred per unit charge between two points in a circuit.
电压，也叫电势差，测量电路中两点之间每单位电荷转移的能量。
The unit of voltage is the volt, symbol V. In equations, voltage is usually represented by V.
电压的单位是伏特，符号为 V。在公式中，电压通常用 V 表示。
A common mark scheme answer is that voltage is the energy transferred per coulomb of charge. Examiners look for the phrase 'energy per unit charge' rather than 'force' or 'speed of electrons'.
常见的评分方案答案是电压是每库仑电荷转移的能量。阅卷老师寻找的是“每单位电荷的能量”这一表述，而不是“力”或“电子速度”。
A cell or battery provides voltage to push electrons around a complete circuit. Without a source of voltage, no current flows.
电池或电源提供电压以推动电子在闭合电路中流动。没有电压源，就不会有电流。
Some students confuse voltage with current. A mark scheme answer that says 'voltage pushes current around the circuit' can still gain partial credit, but 'voltage is the energy per unit charge' is the precise wording.
一些学生混淆电压和电流。如果答案说“电压推动电流在电路中流动”，评分方案可能仍给予部分分数，但“电压是每单位电荷的能量”才是精确表述。
3. Measuring Current with an Ammeter | 用安培计测量电流
An ammeter is used to measure current. It must be connected in series with the component being tested, so that the same current passes through both.
安培计用于测量电流。它必须与被测元件串联，这样相同的电流才会通过两者。
A mark scheme typically gives one mark for 'series connection' and one mark for 'ammeter' if the symbol or name is required.
评分方案通常给一分给“串联连接”，如果要求符号或名称，再给一分给“安培计”。
The ideal ammeter has zero resistance so it does not reduce the current it is measuring. In KS3 answers, saying 'low resistance' is acceptable.
理想安培计的电阻为零，因此不会减小它正在测量的电流。在 KS3 答案中，说“低电阻”是可以接受的。
Common error: placing the ammeter in parallel. This could create a short circuit or give an incorrect reading, so mark schemes penalise this.
常见错误：将安培计并联。这可能造成短路或读数错误，因此评分方案会扣分。
When drawing a circuit diagram, the ammeter symbol should be a circle with the letter A inside. A mark is often awarded only if the symbol is drawn clearly and in series with the rest of the loop.
绘制电路图时，安培计符号应为一个圆圈，内部写有字母 A。通常只有符号画得清晰且串联在回路中，才能得分。
4. Measuring Voltage with a Voltmeter | 用伏特计测量电压
A voltmeter measures the potential difference across a component. It must be connected in parallel with the component.
伏特计测量元件两端的电势差。它必须与元件并联。
In mark schemes, one mark is usually awarded for 'parallel connection' and another for naming the instrument 'voltmeter'.
在评分方案中，通常给一分给“并联连接”，再给一分给说出仪器名称“伏特计”。
The ideal voltmeter has very high resistance so that very little current passes through it. This prevents the voltmeter from changing the circuit behaviour.
理想伏特计的电阻非常大，因此几乎没有电流通过它。这可以防止伏特计改变电路行为。
Common error: connecting the voltmeter in series. This would increase the total resistance and can stop the circuit from working normally.
常见错误：将伏特计串联。这会增加总电阻，并可能使电路无法正常工作。
The voltmeter symbol is a circle with a V inside. In mark schemes, it must be drawn with two clearly separate connections across the component, not in line with it.
伏特计符号是圆圈内有 V。在评分方案中，它必须画成与元件两端清晰连接，而不是与元件在同一条线上。
5. Current in Series Circuits | 串联电路中的电流
In a series circuit, there is only one loop for charge to flow around. The current is the same at every point in the circuit.
在串联电路中，电荷只有一条回路可流动。电路中各点的电流都相同。
A mark scheme answer may state: 'The current is the same everywhere in a series circuit.' One mark is awarded for this idea.
评分方案答案可能是：“串联电路中各处的电流相同。”这个观点给一分。
Adding more cells in series increases the total voltage, which increases the current if the resistance stays the same.
串联更多电池会增加总电压，如果电阻不变，电流会增大。
Adding more bulbs in series increases the total resistance, so the current decreases and all bulbs become dimmer.
串联更多灯泡会增加总电阻，因此电流减小，所有灯泡都变暗。
If an ammeter is placed before or after a bulb in a series circuit, it will read the same value. Mark schemes expect candidates to know that position does not affect the reading.
在串联电路中，安培计放在灯泡之前或之后读数相同。评分方案期望考生知道位置不影响读数。
6. Current in Parallel Circuits | 并联电路中的电流
In a parallel circuit, the current splits at each junction and rejoins later. The total current from the cell equals the sum of the currents in the separate branches.
在并联电路中，电流在每个节点处分流，之后重新汇合。电池流出的总电流等于各支路电流之和。
Mark schemes often give one mark for 'current splits' and one mark for 'sum of branch currents equals total current'.
评分方案通常给一分给“电流分流”，再给一分给“各支路电流之和等于总电流”。
If two identical bulbs are connected in parallel, the current through each bulb is half of the total current supplied by the cell.
如果两个相同的灯泡并联，则通过每个灯泡的电流是电池提供总电流的一半。
Removing one branch in a parallel circuit increases the total resistance, so the total current from the battery decreases, but the remaining branch is unaffected.
在并联电路中移除一条支路会增加总电阻，因此电池提供的总电流减小，但其余支路不受影响。
In mark schemes, a statement like 'the current is shared between the branches' is acceptable, but adding that 'the total current is conserved' makes the answer stronger.
在评分方案中，像“电流在支路之间分配”这样的表述是可以接受的，但加上“总电流守恒”会让答案更有力。
7. Voltage in Series Circuits | 串联电路中的电压
In a series circuit, the total voltage from the cell is shared between the components. The sum of the voltages across each component equals the cell voltage.
在串联电路中，电池的总电压在元件之间分配。每个元件两端的电压之和等于电池电压。
A mark scheme answer might be: 'The supply voltage is divided between the components in series.' This gains one mark.
评分方案答案可能是：“电源电压在串联的元件之间分配。”这可得一分。
If two identical bulbs are in series with a 6 V cell, each bulb receives 3 V because the voltage is shared equally.
如果两个相同的灯泡与 6 V 电池串联，每个灯泡得到 3 V，因为电压平均分配。
If one component has a higher resistance than another in series, it will receive a larger share of the voltage.
如果串联的一个元件比另一个电阻大，它将获得更大的电压份额。
Mark schemes often expect students to use the phrase 'voltage is shared' rather than 'voltage is used up' because the energy is transferred, not destroyed.
评分方案通常期望学生使用“电压被分配”而不是“电压被用尽”，因为能量是转移的，不是消失的。
8. Voltage in Parallel Circuits | 并联电路中的电压
In a parallel circuit, each branch receives the full voltage of the cell. The voltage across each branch is the same.
在并联电路中，每条支路都获得电池的全部电压。各支路两端的电压相同。
Mark schemes often award one mark for stating that 'the voltage is the same across all branches in parallel'.
评分方案通常给一分给“并联电路中所有支路两端的电压相同”。
This explains why household appliances are connected in parallel: each appliance receives the full mains voltage regardless of others being switched on or off.
这解释了为什么家用电器采用并联连接：每台电器都获得完整的电源电压，而不管其他电器是否开关。
A common exam question asks why bulbs in parallel are brighter than in series. Acceptable answer: in parallel each bulb gets the full cell voltage, so it operates at full brightness.
常见考题问为什么并联的灯泡比串联的更亮。可接受的答案：并联时每个灯泡获得电池的全部电压，因此以最大亮度工作。
If a cell is 9 V and one branch has a single bulb, that bulb has 9 V across it. Adding more branches does not reduce this voltage.
如果电池是 9 V，一条支路中只有一个灯泡，则该灯泡两端为 9 V。增加更多支路不会降低这个电压。
9. Circuit Symbols and Common Mark Scheme Errors | 电路符号与常见评分错误
Students must be able to draw and recognise standard circuit symbols for cell, battery, switch, lamp, ammeter, voltmeter, resistor and connecting wire.
学生必须能够绘制和识别电池、电源、开关、灯泡、安培计、伏特计、电阻和导线的标准电路符号。
In mark schemes, a symbol is only awarded the mark if it is drawn correctly. For example, an ammeter symbol should be a circle with an A inside, not a box labelled 'ammeter'.
在评分方案中，只有符号画正确才能得分。例如，安培计符号应是圆圈内有 A，而不是标有
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