📚 GCSE Edexcel Physics: Electric Current | GCSE Edexcel 物理：电流 考点精讲
Mastering electric current is fundamental to understanding circuits in GCSE Edexcel Physics. This guide breaks down the key concepts around charge, current, and the rules that govern series and parallel circuits. You will learn the definition of current, the equation I = Q / t, how to use an ammeter correctly, and how current behaves in different circuit layouts.
掌握电流是理解 GCSE Edexcel 物理电路内容的基础。本文精讲电荷、电流以及串并联电路法则等核心考点。你将学习电流的定义、公式 I = Q / t、正确使用安培表的方法，以及电流在不同电路结构中的行为规律。
1. The Atom and Charge Carriers | 原子与电荷载体
All matter is made up of atoms. An atom consists of a tiny central nucleus containing positively charged protons and neutral neutrons. Negatively charged electrons orbit the nucleus in shells. In a conductor, such as a copper wire, some of the outer electrons are only loosely bound to their atoms and can move freely throughout the material. These mobile electrons are known as free electrons or charge carriers.
所有物质都由原子构成。原子中央是一个微小的原子核，含有带正电的质子和不带电的中子。带负电的电子在核外的壳层中运动。在导体（如铜导线）中，部分外层电子受原子束缚较弱，可以在材料中自由移动。这些可移动的电子被称为自由电子或电荷载体。
An electric current is simply a flow of these charge carriers. In metals, current is due to the movement of electrons. In other materials, such as electrolytes, both positive and negative ions can act as charge carriers.
电流本质上就是这些电荷载体的流动。在金属中，电流源于电子的移动。而在其他材料（如电解质）中，正负离子均可充当电荷载体。
2. What is Electric Current? | 什么是电流？
Electric current is defined as the rate of flow of electric charge. If a large amount of charge passes a point in a circuit in a short time, the current is large. The size of the current tells you how many coulombs of charge pass each second.
电流被定义为单位时间内通过导体某一横截面的电荷量。如果在短时间内有大量电荷通过电路中的某一点，则电流较大。电流的大小反映了每秒钟通过多少库仑的电荷。
In a simple circuit, chemical energy from a cell pushes free electrons around the conducting path. The electrons drift slowly, but the electric effect travels almost instantly, causing all components to start working at nearly the same time.
在简单电路中，电池的化学能推动自由电子沿导线移动。电子本身漂移速度很慢，但电场效应几乎瞬间传递，使所有元件几乎同时开始工作。
3. Equation: I = Q / t | 公式 I = Q / t
The relationship between current, charge and time is given by the equation:
电流、电荷和时间的关系由以下公式给出：
I = Q / t
Where I is the current in amperes (A), Q is the charge in coulombs (C), and t is the time in seconds (s).
其中 I 是电流，单位安培（A）；Q 是电荷量，单位库仑（C）；t 是时间，单位秒（s）。
To find charge or time, simply rearrange the equation: Q = I × t and t = Q / I. A typical exam question might ask: A current of 0.4 A flows through a lamp for 5 minutes. How much charge passes through the lamp? (Remember to convert minutes to seconds: 5 minutes = 300 seconds, so Q = 0.4 × 300 = 120 C).
要求电荷或时间，只需变形公式：Q = I × t 以及 t = Q / I。典型考题：电流 0.4 A 流过灯泡 5 分钟，问通过灯泡的电荷量为多少？（注意时间换算成秒：5 min = 300 s，则 Q = 0.4 × 300 = 120 C）。
GCSE questions often test unit conversions and rearranging the equation, so practise using triangles or algebraic methods to become confident.
GCSE 考题经常考查单位换算和公式变形，因此要熟练运用公式三角或代数方法进行转换。
4. Units of Current: The Ampere | 电流单位：安培
The SI unit of electric current is the ampere, often shortened to amp (A). One ampere is defined as the current that flows when one coulomb of charge passes a point in one second. Smaller currents are measured in milliamperes (mA), where 1 A = 1000 mA.
电流的国际单位是安培，简写为 A。1 安培定义为每秒有 1 库仑的电荷通过导体某一横截面。较小的电流用毫安（mA）表示，1 A = 1000 mA。
Since the charge on a single electron is approximately 1.6 × 10⁻¹⁹ C, a current of 1 A corresponds to roughly 6.25 × 10¹⁸ electrons flowing past a point per second. This enormous number helps to show that even a small current involves a vast number of moving electrons.
由于单个电子的电荷量约为 1.6 × 10⁻¹⁹ C，1 A 的电流大约相当于每秒有 6.25 × 10¹⁸ 个电子通过某一点。这个巨大的数字说明，即使很小的电流也涉及海量电子的移动。
5. Direction of Current | 电流的方向
There are two ways to describe the direction of current: conventional current and electron flow. Conventional current is defined as flowing from the positive terminal to the negative terminal of a cell or battery. This convention was established before scientists discovered the electron and is still used in circuit diagrams and calculations.
描述电流方向有两种方式：传统电流方向和电子流方向。传统电流方向定义为从电池正极流向负极。这个规定是在科学家发现电子之前确立的，如今仍用于电路图和计算中。
Electron flow is the actual movement of electrons in a metal conductor. Because electrons are negatively charged, they are repelled by the negative terminal and attracted to the positive terminal. Therefore, electrons flow from negative to positive, opposite to the conventional direction. At GCSE level, you will usually use conventional current, but you should be aware of this historical detail.
电子流是金属导体中电子的实际运动方向。由于电子带负电，它们被负极排斥并被正极吸引，因此电子从负极流向正极，与传统方向相反。在 GCSE 阶段，你通常使用传统电流方向，但也应了解这一历史背景。
6. Measuring Current with an Ammeter | 用安培表测量电流
An ammeter is the instrument used to measure electric current. It must always be connected in series with the component whose current you wish to measure. This means the ammeter becomes part of the single conducting loop, and all the charge flowing through the component also flows through the ammeter.
安培表是用来测量电流的仪表。它必须始终与被测元件串联。这意味着安培表成为单一回路的一部分，流过元件的所有电荷也会流过安培表。
When connecting an ammeter, the positive (red) terminal should be connected towards the positive side of the cell, and the negative (black) terminal towards the negative side. Connecting an ammeter in parallel would create a very low-resistance path, causing a large current to flow and potentially damaging the meter.
连接安培表时，正接线柱（红）应朝向电池正极侧，负接线柱（黑）朝向负极侧。如果将安培表并联连接，会产生一条电阻极低的通路，导致大电流流过，可能损坏仪表。
In GCSE practicals, you will often use digital or moving‑coil ammeters. The reading is taken directly in amperes or milliamperes, depending on the scale selected.
在 GCSE 实验中，你经常会使用数字或磁电式安培表。根据所选量程，可直接读取安培或毫安数值。
7. Current in Series Circuits | 串联电路中的电流
In a series circuit, there is only one path for current to flow. Because of this, the electric current is the same at all points in the circuit. Whether you measure the current between the cell and a resistor, or between two resistors, the ammeter will give an identical reading.
在串联电路中，电流只有一条通路。因此，电路中各点的电流都相等。无论你在电池与电阻之间，还是在两个电阻之间测量电流，安培表的读数都完全相同。
This can be expressed as: I₁ = I₂ = I₃ = … where I₁, I₂, I₃ are the currents at different positions. The components share the total potential difference but the current remains constant throughout.
这可以表示为：I₁ = I₂ = I₃ = …，其中 I₁、I₂、I₃ 是不同位置的电流。元件分担总电势差，但电流处处恒定。
Even if you add more resistors or bulbs in series, the current through each component will still be identical, though its magnitude will decrease as the total resistance increases.
即使串联更多的电阻或灯泡，每个元件的电流仍然相等，只是其大小会随总电阻增加而减小。
8. Current in Parallel Circuits | 并联电路中的电流
A parallel circuit provides more than one path for current. The current splits at each junction, with some flowing through each branch. The total current leaving the source equals the sum of the currents in the separate branches. This is a consequence of the conservation of charge.
并联电路提供多条电流路径。电流在每个节点分流，部分电流流过各条支路。离开电源的总电流等于各支路电流之和，这是电荷守恒的结果。
This can be written as: Itotal = I₁ + I₂ + I₃ + … For example, if a main circuit carries 3 A and splits into two branches where one branch has 1.2 A, the other branch must have 3 A – 1.2 A = 1.8 A.
可以写为：Itotal = I₁ + I₂ + I₃ + … 例如，若干路电流为 3 A，分流进入两条支路，其中一条支路为 1.2 A，则另一条支路必定为 3 A – 1.2 A = 1.8 A。
In a parallel circuit, the current in each branch may be different depending on the resistance of that branch. The branch with lower resistance carries a larger current.
在并联电路中，各支路的电流可能因电阻不同而不同。电阻较小的支路通过的电流较大。
9. Current, Potential Difference and Resistance | 电流、电势差与电阻
The size of the current in a circuit is determined by two factors: the potential difference (voltage) provided by the cell, and the total resistance of the circuit. These quantities are linked by Ohm’s law: I = V / R, where V is the potential difference in volts (V) and R is the resistance in ohms (Ω).
电路中电流的大小取决于两个因素：电池提供的电势差（电压）和电路的总电阻。这些物理量通过欧姆定律关联：I = V / R，其中 V 是电势差（单位伏特 V），R 是电阻（单位欧姆 Ω）。
For a given resistance, increasing the potential difference drives a higher current. Conversely, for a fixed potential difference, a larger resistance reduces the current. This relationship is essential when analysing both series and parallel circuits.
对于给定的电阻，增大电势差会驱动更大的电流。反过来，当电势差固定时，电阻增大会使电流减小。在分析串并联电路时，这一关系至关重要。
10. Charge Conservation and Circuit Rules | 电荷守恒与电路法则
The rules for current in series and parallel circuits stem directly from the principle of conservation of electric charge. Charge cannot be created or destroyed, so the total amount of charge entering a junction each second must equal the total amount leaving it.
串并联电路中电流的规律直接源于电荷守恒原理。电荷不能被创造或消灭，所以每秒钟进入节点的总电荷量必定等于离开节点的总电荷量。
This is why the current before a junction equals the sum of the currents after it in a parallel circuit, and why the current is undiminished around a series loop. The charge carriers are not used up; they simply transfer energy to the components.
这就是为什么并联电路中节点前的电流等于节点后各支路电流之和，以及为什么串联环路中电流不会减小。电荷载体不会被消耗，它们只是将能量传递给元件。
Understanding this conservation principle helps you to avoid common mistakes, such as thinking that some current is lost after passing through a lamp. In reality, the same number of electrons flow out as flow in; they just have less energy.
理解这一守恒原理有助于避免常见误区，比如认为电流通过灯泡后会减少。事实上，流出的电子数量与流入的相同，只是它们的能量降低了。
Published by TutorHao | Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导