📚 Electricity: Charge, Current and Circuits | 电学：电荷、电流与电路
In the Edexcel IGCSE (9-1) Physics specification, the topic of electricity is central to understanding how charge moves in circuits and how electrical energy is transferred. This article covers the key concepts from the Student Book by Brian Arnold, Penny Johnson and Steve Woolley, including charge, current, potential difference, resistance, circuit rules, power and electrical safety.
在 Edexcel IGCSE（9-1）物理考纲中，电学是理解电荷如何在电路中移动以及电能如何转化的核心内容。本文涵盖《学生用书》中的关键概念，包括电荷、电流、电势差、电阻、电路规则、电功率和用电安全。
1. Electric Charge and Current | 电荷与电流
Electric charge is a fundamental property of matter. The unit of charge is the coulomb (C). An electric current is the rate of flow of charge. In a metal wire, current is carried by negatively charged electrons, but conventional current is defined as the flow of positive charge, so it points in the opposite direction to electron flow.
电荷是物质的基本属性。电荷的单位是库仑（C）。电流是电荷流动的速率。在金属导线中，电流由带负电的电子携带，但常规电流被定义为正电荷的流动方向，因此它与电子流动的方向相反。
Current, charge and time are linked by the equation:
电流、电荷和时间的关系式为：
Q = I × t
where Q is charge in coulombs, I is current in amperes (A), and t is time in seconds (s). In metals, the electrons move slowly in one direction, but the electric signal travels close to the speed of light.
其中 Q 是电荷（库仑），I 是电流（安培 A），t 是时间（秒 s）。在金属中，电子沿一个方向缓慢漂移，但电场信号以接近光速传播。
2. Circuit Symbols and Diagrams | 电路符号与电路图
Circuit diagrams use standard symbols so that everyone can understand them. You need to recognise and draw the symbols for a cell, battery, switch, lamp, resistor, variable resistor, ammeter, voltmeter, fuse and diode.
电路图使用标准符号，以便所有人都能理解。你需要识别并画出电池、单节电池、开关、灯泡、电阻器、可变电阻器、电流表、电压表、保险丝和二极管的符号。
- Ammeters are always connected in series so that they measure the current through a component.
- 电流表总是串联连接，以便测量通过元件的电流。
- Voltmeters are always connected in parallel so that they measure the potential difference across a component.
- 电压表总是并联连接，以便测量元件两端的电势差。
A correct circuit diagram is neat, uses straight lines for wires and does not show components overlapping.
正确的电路图应整洁，导线用直线表示，并且元件不重叠。
3. Potential Difference and EMF | 电势差与电动势
Potential difference (p.d.) is the work done per unit charge as charge moves between two points in a circuit. It is measured in volts (V). One volt means one joule of energy is transferred per coulomb of charge.
电势差（p.d.）是单位电荷在电路中两点之间移动时所做的功。它用伏特（V）测量。1 伏表示每库仑电荷转移 1 焦耳能量。
V = W ÷ Q
where V is potential difference, W is work done or energy transferred in joules, and Q is charge in coulombs.
其中 V 是电势差，W 是做功或转移能量（焦耳），Q 是电荷（库仑）。
EMF (electromotive force) is the energy supplied by a source such as a battery per unit charge. It is also measured in volts. In an ideal circuit with no internal resistance, the terminal p.d. equals the EMF.
电动势（EMF）是电池等电源提供给每单位电荷的能量，也用伏特测量。在无内阻的理想电路中，路端电压等于电动势。
4. Resistance and Ohm's Law | 电阻与欧姆定律
Resistance is the opposition to current flow. The unit of resistance is the ohm (Ω). Resistance is defined by the ratio of potential difference to current.
电阻是对电流的阻碍作用。电阻的单位是欧姆（Ω）。电阻由电势差与电流的比值定义。
R = V ÷ I
A component obeys Ohm's law if its resistance remains constant when temperature is constant. For an ohmic conductor, the current is directly proportional to the potential difference, so the I-V graph is a straight line through the origin.
如果元件的电阻在温度不变时保持恒定，则该元件遵循欧姆定律。对于欧姆导体，电流与电势差成正比，因此 I-V 图是一条过原点的直线。
Resistance depends on the material, length, cross-sectional area and temperature of a wire. Longer wires have greater resistance; thicker wires have less resistance.
电阻取决于导线的材料、长度、横截面积和温度。导线越长，电阻越大；导线越粗，电阻越小。
5. I-V Characteristics | 电流-电压特性
Different components have different I-V graphs. A fixed resistor at constant temperature is ohmic and gives a straight line through the origin. A filament lamp has a curved graph because its resistance increases as the filament heats up.
不同元件的 I-V 图不同。温度恒定的定值电阻是欧姆导体，给出过原点的直线。白炽灯的曲线是弯曲的，因为灯丝受热后电阻增大。
A diode only allows current to pass in one direction. Its I-V graph shows almost no current in reverse bias, and a sharp increase in current in forward bias once the threshold voltage is exceeded.
二极管只允许电流沿一个方向通过。它的 I-V 图显示反向偏置时几乎没有电流，正向偏置超过阈值电压后电流急剧增大。
For a filament lamp, the increasing resistance can be explained by the metal ions vibrating more at higher temperature, so electrons collide more often.
对于白炽灯，电阻增大可解释为温度升高时金属离子振动更剧烈，使电子碰撞更频繁。
6. Series Circuits | 串联电路
In a series circuit, components are connected end to end in one loop. The current is the same at all points because there is only one path for the charge to flow.
在串联电路中，各元件首尾相连形成单一回路。因为电荷只有一条路径可走，所以电路中各处的电流相同。
The total potential difference across the circuit is shared between the components. The sum of the p.d.s across the components equals the supply p.d.
电路两端的总电势差被各元件分担。各元件两端电势差之和等于电源电势差。
The total resistance in a series
Published by TutorHao | IB Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图