📚 KS3 CIE Circuits and Symbols | KS3 CIE 电路与符号
Electric circuits are the foundation of modern technology. In KS3 CIE Science, you learn how to use standard symbols to represent components and how to predict the behaviour of simple circuits. This guide covers the key ideas, symbols and safety rules you need for the Checkpoint and beyond.
电路是现代技术的基础。在 KS3 CIE 科学课程中，你将学习如何使用标准符号表示元件，以及如何预测简单电路的行为。本指南涵盖 Checkpoint 考试及后续学习所需的关键概念、符号和安全规则。
1. What is an Electric Circuit? | 什么是电路？
An electric circuit is a complete, closed path through which electric charge can flow. For a circuit to work, it must include a source of energy, such as a cell or battery, and a load, such as a lamp or buzzer. If there is a break anywhere in the loop, charge cannot flow and the circuit is described as open or incomplete.
电路是电荷可以通过的完整闭合路径。电路要工作，必须包含能量源（例如电池或电池组）和负载（例如灯泡或蜂鸣器）。如果回路中任何位置出现断开，电荷就无法流动，这种电路称为开路或不完整电路。
Charge is carried by tiny particles called electrons. In a metal wire, electrons move from the negative terminal of the cell, around the circuit, and back to the positive terminal. This movement of charge is called an electric current.
电荷由称为电子的微小粒子携带。在金属导线中，电子从电池的负极出发，绕电路一周，回到正极。这种电荷的移动称为电流。
2. Common Circuit Symbols | 常见电路符号
Circuit diagrams use standard symbols so that anyone can read them. You must be able to recognise and draw the symbols for a cell, a battery, a lamp, a switch, a buzzer, a resistor, a variable resistor, an ammeter, a voltmeter and connecting wires.
电路图使用标准符号，以便任何人都能看懂。你必须能够识别并绘制电池、电池组、灯泡、开关、蜂鸣器、电阻、可变电阻、电流表、电压表和导线的符号。
| Component | Symbol description | 中文名称 |
|---|---|---|
| Cell | Long line (+) and short line (-) | 电池 |
| Battery | Two or more cells joined | 电池组 |
| Lamp | Circle with a cross inside | 灯泡 |
| Switch (open) | Break in the line with a small gap | 开关（断开） |
| Switch (closed) | Line connected across the gap | 开关（闭合） |
| Resistor | Rectangle | 电阻 |
| Variable resistor | Rectangle with an arrow | 可变电阻 |
| Ammeter | Circle with A inside | 电流表 |
| Voltmeter | Circle with V inside | 电压表 |
| Buzzer | Half-circle with two lines | 蜂鸣器 |
When drawing symbols, use a ruler and make clear, sharp lines. Do not sketch or use artistic pictures. The symbols must be connected by straight wires, and corners should be right angles.
画符号时，请使用直尺，画出清晰、锐利的线条。不要画草图或艺术图。符号之间必须用直线导线连接，转角应为直角。
3. Drawing Circuit Diagrams | 绘制电路图
A good circuit diagram is neat, rectangular and easy to follow. Start by placing the cell or battery on the left, then draw the rest of the components around a single loop. Avoid crossing wires unless absolutely necessary.
好的电路图应整洁、呈矩形且易于理解。先把电池或电池组放在左侧，然后围绕单一回路绘制其他元件。除非必要，避免导线交叉。
Use the correct symbols and label each component if the question asks. Remember that a closed switch allows current to flow, while an open switch stops the current. Circuit diagrams are read from the positive terminal of the cell, through the components, and back to the negative terminal.
使用正确的符号，如果题目要求就标注每个元件。记住闭合开关允许电流通过，而断开开关阻止电流。电路图从电池正极开始读，经过各元件，回到负极。
4. Series and Parallel Circuits | 串联和并联电路
In a series circuit, components are connected one after another in a single loop. If one component breaks, the whole circuit stops working because the loop is broken. The current is the same at every point in a series circuit.
在串联电路中，元件一个接一个连接在单一回路中。如果一个元件损坏，整个电路就会停止工作，因为回路断了。串联电路中各点的电流相同。
In a parallel circuit, components are connected in separate branches. Each branch has its own path for current. If one branch breaks, the other branches can still work. The total current from the cell is shared between the branches.
在并联电路中，元件连接在不同的支路中。每条支路都有自己的电流路径。如果一条支路断开，其他支路仍可工作。电池提供的总电流在各支路之间分配。
Series circuits are simple but less reliable. Parallel circuits are used in home lighting because one lamp failing does not make all the others go out.
串联电路简单但可靠性较低。家庭照明使用并联电路，因为一盏灯坏了不会导致其他灯都熄灭。
5. Current in a Circuit | 电路中的电流
Electric current is the rate of flow of electric charge. It is measured in amperes, or amps, with the symbol A. An ammeter is connected in series with the component so that the current passes through it.
电流是电荷流动的速率。电流以安培（简称安）为单位，符号为 A。电流表与元件串联连接，使电流通过它。
Current can be calculated using the equation:
电流可用以下公式计算：
I = Q ÷ t
Where I is current in amps (A), Q is charge in coulombs (C), and t is time in seconds (s).
其中 I 是电流（安培 A），Q 是电荷量（库仑 C），t 是时间（秒 s）。
In a series circuit, the current is the same everywhere. In a parallel circuit, the current from the cell equals the sum of the currents in all the branches.
在串联电路中，各处电流相同。在并联电路中，电池输出的电流等于所有支路电流之和。
6. Voltage and Energy | 电压与能量
Voltage is a measure of the energy transferred to or from the charges as they move around a circuit. It is measured in volts with the symbol V. A voltmeter is connected in parallel across a component to measure the voltage difference across it.
电压是电荷在电路中移动时获得或转移的能量的量度。电压以伏特为单位，符号为 V。电压表并联连接在元件两端，以测量该元件两端的电压差。
The voltage across a cell or battery is sometimes called its potential difference or electromotive force. In a series circuit, the voltages across the components add up to the voltage of the cell. In a parallel circuit, each branch has the same voltage as the cell.
电池或电池组两端的电压有时称为电势差或电动势。在串联电路中，各元件两端的电压之和等于电池电压。在并联电路中，每条支路两端的电压与电池电压相同。
Voltage can be linked to energy by the equation:
电压与能量的关系可用公式表示：
V = W ÷ Q
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