Electromagnetic Induction | 电磁感应

📚 Electromagnetic Induction | 电磁感应

Electromagnetic induction is a fundamental concept in IB Physics that describes how a changing magnetic field can generate an electromotive force (emf) in a conductor. This phenomenon forms the basis of generators, transformers, and many everyday technologies. In this revision guide, we will break down the core principles, equations, and exam strategies you need to master electromagnetic induction.

电磁感应是 IB 物理中的一个核心概念，它描述了变化的磁场如何在导体中产生电动势。这一现象是发电机、变压器以及许多日常技术的基础。在本复习指南中，我们将系统梳理电磁感应的核心原理、方程和考试策略，帮助你掌握这一板块。

1. Magnetic Flux and Magnetic Flux Density | 磁通量与磁通密度

Magnetic flux is a measure of the total magnetic field lines passing through a surface. For a uniform magnetic field of flux density B, on a plane area A with angle θ between the field direction and the normal to the plane, the flux is:

磁通量是穿过某一表面的磁场线总量的度量。对于磁感应强度大小为 B 的均匀磁场，面积为 A 的平面，当磁场方向与平面法线方向的夹角为 θ 时，磁通量为：

Φ = BA cosθ

In SI units, the magnetic flux is measured in webers (Wb), where 1 Wb = 1 T·m². The flux density B is therefore sometimes called magnetic induction, and it can be interpreted as the flux per unit area for a surface perpendicular to the field.

在国际单位制中，磁通量的单位是韦伯（Wb），1 Wb = 1 T·m²。因此磁感应强度 B 又可理解为垂直穿过单位面积的磁通量，即磁通密度。

When the angle θ changes, the flux changes. For example, if a coil rotates in a uniform magnetic field, the flux varies as Φ = BA cos(ωt), producing a sinusoidal emf in a generator.

当夹角 θ 改变时，磁通量也随之改变。例如，线圈在均匀磁场中旋转时，磁通量按 Φ = BA cos(ωt) 变化，从而在发电机中产生正弦式电动势。

2. Faraday’s Law of Induction | 法拉第电磁感应定律

Faraday’s law states that the magnitude of the induced emf in a circuit equals the rate of change of magnetic flux linkage through the circuit. The flux linkage is NΦ, where N is the number of turns. Mathematically:

法拉第定律表明，回路中感应电动势的大小等于穿过回路的

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