Electric Current | 电流

📚 Electric Current | 电流

Electric current is the flow of electric charge. In a circuit, it is the rate at which charge passes a point, and understanding current is fundamental to explaining how circuits work. This article covers the key concepts of electric current for IGCSE Edexcel Physics, from charge carriers to current in series and parallel circuits.

电流是电荷的流动。在电路中，它是电荷通过某一点的速率，理解电流是解释电路工作原理的基础。本文涵盖了IGCSE Edexcel物理中电流的关键概念，从电荷载体到串联和并联电路中的电流。

1. What is Electric Current? | 什么是电流？

Electric current is the net flow of electric charge. In metal wires, the moving charges are electrons. A current exists when there is a potential difference (voltage) across a conductor, giving electrons the energy to drift in one direction. Although electrons move slowly, the electric signal travels almost at the speed of light.

电流是电荷的净流动。在金属导线中，移动的电荷是电子。当导体两端存在电势差（电压）时，就会产生电流，电压给电子提供能量使其向一个方向漂移。尽管电子移动缓慢，但电信号几乎以光速传播。

2. Charge Carriers | 电荷载体

In solid metal conductors, the charge carriers are free electrons that are not bound to any particular atom. These delocalised electrons can move through the lattice when an electric field is applied. In liquids and gases, both positive ions and negative ions or electrons can act as charge carriers, carrying current in opposite directions.

在固体金属导体中，电荷载体是不受任何特定原子束缚的自由电子。当施加电场时，这些离域电子可以在晶格中移动。在液体和气体中，正离子和负离子或电子都可以作为电荷载体，朝相反方向传导电流。

3. Definition of Current | 电流的定义

Current (I) is defined as the rate of flow of charge. If a charge Q passes a point in a time t, the current is given by the equation:

I = Q / t

where I is current in amperes (A), Q is charge in coulombs (C), and t is time in seconds (s). A current of 1 ampere means 1 coulomb of charge flows past a point every second.

电流（I）定义为电荷的流动速率。如果电荷Q在时间t内通过某一点，则电流由以下公式给出：

I = Q / t

其中I为电流，单位为安培（A）；Q为电荷，单位为库仑（C）；t为时间，单位为秒（s）。1安培的电流意味着每秒有1库仑的电荷通过某一点。

4. Unit of Current: The Ampere | 电流的单位：安培

The SI unit of current is the ampere, usually shortened to ‘amp’ (symbol A). One ampere is equivalent to one coulomb per second. In circuits, current is often measured in milliamperes (1 mA = 10⁻³ A) or microamperes (1 µA = 10⁻⁶ A) for small currents, or kiloamperes (1 kA = 10³ A) for very large currents.

电流的国际单位是安培，通常简称为“安”（符号A）。1安培等于每秒1库仑。在电路中，小电流通常用毫安（1 mA = 10⁻³ A）或微安（1 µA = 10⁻⁶ A）来度量，非常大的电流则用于千安（1 kA = 10³ A）。

5. Direction of Current | 电流的方向

Conventional current flows from the positive terminal to the negative terminal of a power supply. This convention was established before the discovery of the electron. In reality, electrons flow from negative to positive. In circuit analysis, we still use conventional current direction; the movement of electrons is called electron flow and is opposite to conventional current.

常规电流从电源的正极流向负极。这个惯例是在发现电子之前确立的。实际上，电子从负极流向正极。在电路分析中，我们仍然使用常规电流方向；电子的移动称为电子流，与常规电流方向相反。

6. Measuring Current with an Ammeter | 用安培表测量电流

Current is measured using an ammeter, which must be connected in series with the component through which the current is to be measured. The ammeter should have a very low resistance so that it does not significantly affect the circuit. Ideal ammeters have zero resistance. Make sure the positive terminal of the ammeter is connected towards the positive side of the supply for DC circuits.

电流使用安培表来测量，安培表必须与待测电流的元件串联连接。安培表的内阻应非常低，以免显著影响电路。理想的安培表电阻为零。对于直流电路，确保安培表的正极接线柱朝向电源的正极。

7. Current in Series Circuits | 串联电路中的电流

In a series circuit, the current is the same at all points. There is only one path for charge to flow, so the same number of charges per second pass through each component. If three bulbs are connected in series, an ammeter will read the same value before and after each bulb. The total current is not divided.

在串联电路中，各点的电流都相同。电荷只有一条路径流动，因此每秒通过每个元件的电荷数相同。如果三个灯泡串联，在每个灯泡前后安培表的读数都相同。总电流不会被分配。

8. Current in Parallel Circuits | 并联电路中的电流

In a parallel circuit, the total current from the source splits into the separate branches. The sum of the currents in the branches equals the total current entering the junction. This follows from the conservation of charge. If three identical branches are in parallel, the total current is three times the branch current, provided the branches are identical.

在并联电路中，源自电源的总电流分流到各支路中。各支路电流之和等于进入节点的总电流。这遵循电荷守恒定律。如果三个相同的支路并联，总电流是支路电流的三倍（假设支路完全相同）。

9. Conservation of Charge | 电荷守恒

Charge is conserved in all circuits. At any junction, the total current entering equals the total current leaving. This is Kirchhoff’s first law. It means charge cannot pile up or disappear. In a parallel circuit, the current through the battery is the sum of the currents in all parallel branches.

在所有电路中电荷都是守恒的。在任何节点处，流入的总电流等于流出的总电流。这就是基尔霍夫第一定律。这意味着电荷既不会堆积也不会消失。在并联电路中，通过电池的电流是所有并联支路电流的总和。

10. Calculating Charge | 电荷量的计算

Using I = Q / t, rearrangements give Q = I × t. If a current of 2 A flows for 30 s, the charge transferred is 2 × 30 = 60 C. If a current of 0.5 A flows for 5 minutes, convert time to seconds: t = 5 × 60 = 300 s; then Q = 0.5 × 300 = 150 C. These calculations are common in exams.

使用公式 I = Q / t，变形可得 Q = I × t。若2 A的电流流动30秒，则转移的电荷量为2 × 30 = 60 C。如果0.5 A的电流流动5分钟，则需将时间转换为秒：t = 5 × 60 = 300 s；于是 Q = 0.5 × 300 = 150 C。这类计算在考试中很常见。

11. Factors Affecting Current | 影响电流的因素

The current in a circuit depends on the voltage supplied and the total resistance of the circuit (Ohm’s Law: I = V / R). For a fixed resistance, a higher voltage produces a larger current. For a fixed voltage, a higher resistance reduces the current. Material, length, cross-sectional area and temperature of a wire all affect its resistance and therefore the current.

电路中的电流取决于提供的电压和电路的总电阻（欧姆定律：I = V / R）。对于固定电阻，较高的电压会产生较大的电流。对于固定电压，较高的电阻会减小电流。导线的材料、长度、横截面积和温度都会影响其电阻，从而影响电流。

12. Conductors, Insulators and Semiconductors | 导体、绝缘体和半导体

Conductors contain many free charge carriers, so a large current can flow with a small applied voltage (low resistance). Insulators have very few free charge carriers, so practically no current flows. Semiconductors have intermediate properties; their conductivity can be controlled by adding impurities (doping) or by applying light and heat, which makes them essential in electronics.

导体含有大量自由电荷载体，因此施加较小电压就能产生大电流（电阻小）。绝缘体中自由电荷载体极少，所以实际上没有电流流动。半导体的性质介于两者之间；其导电性可通过掺杂杂质或施加光照和加热来控制，这使它们在电子学中至关重要。

Published by TutorHao | Physics Revision Series | aleveler.com

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