Electric Current | 电流

📚 Electric Current | 电流

Electric current is the rate of flow of electric charge through a conductor. This article covers definitions, charge carriers, drift velocity, potential difference, resistance, resistivity, DC circuits, electromotive force, internal resistance, Kirchhoff’s laws, and electrical power for the CIE A-Level Physics syllabus.

电流是电荷通过导体的流动速率。本文覆盖电流定义、载流子、漂移速度、电势差、电阻、电阻率、直流电路、电动势、内阻、基尔霍夫定律和电功率，符合 CIE A-Level 物理考纲。

1. Electric Charge and Current | 电荷与电流

Electric charge Q is measured in coulombs (C). The elementary charge is e = 1.60 × 10⁻¹⁹ C, so an electron carries −e and a proton carries +e. In a conductor, current is defined as the rate of charge flow past a cross-section.

电荷 Q 的单位是库仑（C）。基本电荷 e = 1.60 × 10⁻¹⁹ C，因此电子带 −e，质子带 +e。在导体中，电流定义为单位时间通过某一横截面的电荷量。

I = ΔQ / Δt

For a steady current this becomes I = Q / t. One ampere is one coulomb per second, so 1 A = 1 C s⁻¹. Because charge is conserved, current is the same at all points in a single loop with no branches.

对于稳定电流，公式可写成 I = Q / t。1 安培等于 1 库仑每秒，即 1 A = 1 C s⁻¹。由于电荷守恒，在无分支的单一回路中，各处电流相同。

2. Conventional Current and Electron Flow | 常规电流与电子流

Conventional current is defined as the direction in which positive charge would move. In metallic conductors, positive ions are fixed in the lattice, and only free electrons move. Therefore electron flow is opposite to conventional current, from negative to positive terminal.

常规电流定义为正电荷流动的方向。在金属导体中，正离子固定在晶格中，只有自由电子移动，因此电子流方向与常规电流相反，从负极到正极。

When circuit diagrams show an arrow for current, that arrow always represents conventional current from the positive terminal, through the external circuit, to the negative terminal. Electrons in the wire move in the opposite direction.

电路图中的电流箭头始终表示常规电流，从正极经过外电路流向负极。导线中的电子实际运动方向与之相反。

3. Measuring Current and the Ampere | 电流的测量与安培

An ammeter measures current and must be placed in series with the component, so the same charge passes through both. An ideal ammeter has zero resistance so it does not change the current it is measuring.

电流表测量电流，必须与元件串联，使相同的电荷通过两者。理想电流表电阻为零，因此不会改变被测电流。

The SI definition of the ampere is based on the force between two parallel current-carrying conductors. For A-Level calculations it is sufficient to use 1 A = 1 C s⁻¹. Digital ammeters often have very low resistance, but not exactly zero.

安培的国际单位制定义基于两根平行载流导体之间的力。在 A-Level 计算中只需使用 1 A = 1 C s⁻¹。数字电流表通常电阻很小，但不完全为零。

4. Charge Carriers and Drift Velocity | 载流子与漂移速度

In a metal, the charge carriers are free electrons. In an electrolyte, both positive and negative ions carry charge. In a semiconductor, electrons and holes both contribute to current.

金属中载流子是自由电子；

Published by TutorHao | A-Level Physics Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）