📚 KS3 CIE Electrical Circuits Exam Questions | KS3 CIE 电路考试题精讲
This revision guide covers the key ideas, skills and question types you will meet in KS3 CIE electrical circuits tests. Use it to check your understanding and practise exam-style questions.
本复习指南涵盖 KS3 CIE 电路测试中的核心概念、技能与常见题型。用它来检查理解并练习考试风格的题目。
1. Circuit Symbols and Basic Ideas | 电路符号与基本概念
You need to recognise and draw the standard circuit symbols used in CIE diagrams. A complete circuit must have a source of energy, a closed conducting path and a component that uses the energy.
你需要认识并画出 CIE 电路图中使用的标准符号。一个完整电路必须有能量源、闭合的导电路径以及消耗能量的元件。
Common symbols include a battery with long and short lines, a lamp as a circle with a cross, a switch as a break in the line that can open or close, and a resistor as a rectangle. An ammeter is a circle with the letter A, and a voltmeter is a circle with the letter V.
常见符号包括：电池用长短线表示，灯泡用带交叉线的圆圈表示，开关用可断开或闭合的线段表示，电阻用矩形表示。电流表是圆圈内写字母 A，电压表是圆圈内写字母 V。
| Component | 元件 | Symbol description | 符号说明 |
|---|---|
| Battery | 电池 | Long line and short line | 长线和短线 |
| Lamp | 灯泡 | Circle with a cross inside | 圆圈内画交叉线 |
| Switch | 开关 | Break in a line with a movable contact | 导线断开处有可动触点 |
| Resistor | 电阻 | Rectangle | 矩形 |
| Ammeter | 电流表 | Circle with A | 圆圈内写 A |
| Voltmeter | 电压表 | Circle with V | 圆圈内写 V |
Always label components clearly when drawing. A gap in the circuit with an open switch means no current flows.
画图时务必清晰标注元件。电路中有断开或开关打开时，电流无法流动。
2. Current, Voltage and Resistance | 电流、电压与电阻
Electric current is the flow of electric charge around a circuit. It is measured in amperes (A) using an ammeter connected in series.
电流是电荷在电路中的流动。它用安培 (A) 为单位，通过串联的电流表测量。
Voltage is the energy transferred per unit charge. It is measured in volts (V) using a voltmeter connected in parallel across a component.
电压是每单位电荷传递的能量。它用伏特 (V) 为单位，通过并联在元件两端的电压表测量。
Resistance opposes the flow of current. It is measured in ohms (Ω). A higher resistance gives a smaller current for the same voltage.
电阻阻碍电流的流动。它用欧姆 (Ω) 为单位。在电压相同时，电阻越大，电流越小。
V = I × R
This equation links voltage, current and resistance. In words, voltage equals current multiplied by resistance.
该公式将电压、电流和电阻联系起来。用文字表达就是电压等于电流乘以电阻。
If you know two quantities, you can find the third by rearranging the equation.
如果已知两个量，可以通过变形公式求出第三个量。
3. Series Circuits | 串联电路
In a series circuit, components are connected one after another in a single loop. The same current flows through every component.
在串联电路中，元件一个接一个地连接在单一回路中。通过每个元件的电流相同。
If one bulb breaks or the switch is opened, the whole circuit stops working because the loop is broken.
如果其中一个灯泡损坏或开关断开，整个电路停止工作，因为回路被切断。
The total resistance in series is the sum of the individual resistances.
串联电路的总电阻等于各电阻之和。
Rₜ = R₁ + R₂ + R₃
The supply voltage is shared between the components in series. Each component receives a portion of the total voltage.
电源电压在串联元件之间分配。每个元件获得总电压的一部分。
Example: two identical lamps in series with a 6 V battery each get about 3 V, and they glow dimmer than a single lamp would.
例如：两个相同灯泡串联在 6 V 电池上，每个灯泡约得到 3 V，比单个灯泡发光更暗。
4. Parallel Circuits | 并联电路
In a parallel circuit, components are connected on separate branches. Each branch gets the full supply voltage.
在并联电路中，元件连接在独立的支路上。每条支路都获得完整的电源电压。
The current from the source splits between the branches. The total current is the sum of the branch currents.
来自电源的电流在支路之间分配。总电流等于各支路电流之和。
If one branch is broken, the other branches can keep working. This is why household circuits are parallel.
如果一条支路断开，其他支路仍可继续工作。这就是家庭电路采用并联方式的原因。
1/Rₜ = 1/R₁ + 1/R₂
Adding more branches in parallel decreases the total resistance and increases the total current from the supply.
并联增加更多支路会减小总电阻并增大来自电源的总电流。
In a parallel circuit, bulbs are usually brighter than in series because each bulb receives the full supply voltage.
在并联电路中，灯泡通常比串联时更亮，因为每个灯泡都获得完整的电源电压。
5. Drawing and Reading Circuit Diagrams | 电路图的绘制与识别
Circuit diagrams should be drawn with straight lines for wires and neat symbols. Avoid unnecessary crossing lines.
电路图应使用直线表示导线，符号要整洁。避免不必要的交叉线。
To identify series and parallel, look for a single loop or multiple loops. Series has one loop; parallel has more than one branch.
识别串联和并联要看是单一回路还是多个回路。串联只有一个回路，并联有多个支路。
When a question gives a diagram, first trace the path from the positive terminal back to the negative terminal. This helps you see which components share the same current or voltage.
当题目给出电路图时，先从正极出发沿路径回到负极。这能帮助你判断哪些元件共享相同的电流或电压。
If two components are on the same wire with no junction between them, they are in series. If they are on separate loops connected to the same two points, they are in parallel.
如果两个元件在同一导线上且中间没有分支点，它们是串联的。如果它们在不同回路但连接在相同两点之间，则是并联的。
6. Ohm's Law Calculations | 欧姆定律计算
be rearranged to I = V ÷ R and R = V ÷ I. Use the correct units: volts, amperes and ohms.
公式 V = I × R 可以变形为 I = V ÷ R 和 R = V ÷ I。使用正确的单位：伏特、安培和欧姆。
Example 1: A 6 V battery is connected across a 3 Ω resistor. Calculate the current.
例题 1：一个 6 V 电池连接一个 3 Ω 电阻。计算电流。
I = V ÷ R = 6 V ÷ 3 Ω = 2 A
Example 2: A lamp has a current of 0.5 A when 4 V is applied. Find its resistance.
例题 2：一个灯泡在 4 V 电压下通过 0.5 A 电流。求它的电阻。
R = V ÷ I = 4 V ÷ 0.5 A = 8 Ω
Example 3: A 9 V battery is connected to a resistor, and the current is 0.3 A. Find the resistance.
例题 3：一个 9 V 电池连接一个电阻，电流为 0.3 A。求电阻。
R = 9 V ÷ 0.3 A = 30 Ω
Always show the formula, substitution and answer with the unit in exam questions. This earns method marks even if the final answer is wrong.
考试中务必写出公式、代入过程和带单位的答案。即使最终答案错误，也能获得步骤分。
7. Measuring Current and Voltage | 电流与电压的测量
An ammeter must be connected in series so the current passes through it. A voltmeter must be connected in parallel across the component being measured.
电流表必须串联连接，让电流通过它。电压表必须并联在被测元件两端。
Connecting an ammeter in parallel or a voltmeter in series is a common error. This can damage the meter or give a false reading.
将电流表并联或
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