📚 6.03 Electromagnetic Effects: Motor Effect and Electromagnetic Induction | 6.03 电磁效应：电动机效应与电磁感应
In this article, we explore the key ideas behind electromagnetic effects as covered in Edexcel IGCSE Science (Physics, Section 6.03). We will look at the motor effect, the DC motor, electromagnetic induction, the AC generator and the transformer. These concepts show how electricity and magnetism are closely linked, and they are regularly tested in the IGCSE examinations.
本文将深入探讨 Edexcel IGCSE 科学（物理部分 6.03）中的电磁效应核心概念。我们将学习电动机效应、直流电动机、电磁感应、交流发电机以及变压器。这些概念展示了电与磁之间的紧密联系，是 IGCSE 考试中的高频考点。
1. Magnetic Fields and Field Lines | 磁场与磁感线
A magnetic field is a region where a magnetic force is exerted on a magnetic material or a moving charge. It is represented by field lines that point from the north pole to the south pole outside a magnet.
磁场是指对磁性材料或运动电荷施加磁力的区域。磁场可以用磁感线来表示，在磁体外部，磁感线从北极指向南极。
- Field lines never cross and their density indicates the strength of the field.
- 磁感线永不相交，其疏密程度表示磁场的强弱。
- In a uniform magnetic field, the field lines are parallel and equally spaced.
- 在匀强磁场中，磁感线相互平行且间距相等。
The direction of the field line gives the direction of the force on a small north pole placed in the field.
磁感线的方向表示放置在磁场中的小磁针北极所受力的方向。
2. The Motor Effect | 电动机效应
A current-carrying wire placed in a magnetic field experiences a force. This is called the motor effect. The wire must be perpendicular to (or have a component perpendicular to) the magnetic field for a force to be produced.
当载流导线被置于磁场中时，导线会受到力的作用，这一现象称为电动机效应。导线必须与磁场方向垂直（或至少有一个垂直分量），才会受到力。
F = B × I × L
Where F is the force (N), B is the magnetic flux density (T), I is the current (A) and L is the length of wire in the field (m).
其中，F 是力（单位：N），B 是磁感应强度（单位：T），I 是电流（单位：A），L 是导线在磁场中的长度（单位：m）。
The size of the force can be increased by increasing the current, using a stronger magnet, or placing more wire inside the magnetic field.
增大电流、使用更强的磁铁或增加处于磁场中导线的长度/匝数，都可以增大这个力。
3. Fleming’s Left-Hand Rule | 弗莱明左手定则
Fleming’s left-hand rule gives the direction of the force on a current-carrying conductor in a magnetic field. Hold the thumb, first finger and second finger of your left hand at right angles to each other.
弗莱明左手定则用于判断磁场中载流导线所受力的方向。将左手的大拇指、食指和中指互相垂直伸直。
- First finger: direction of the magnetic Field (N to S).
- 食指：指向磁场方向（从 N 到 S）。
- Second finger: direction of the Current (conventional current from + to −).
- 中指：指向电流方向（正电荷移动方向，即从 + 到 −）。
- Thumb: direction of the Force (motion).
- 大拇指：指向力的方向（运动方向）。
Remember the order: Field → Current → Force (F, C, F).
记住顺序：磁场 → 电流 → 力（F、C、F）。
4. Forces on a Current-Carrying Coil | 载流线圈受到的力
If a rectangular coil is placed in a magnetic field and a current flows through it, two opposite sides of the coil experience forces in opposite directions. This creates a turning effect, or a couple.
如果矩形线圈被置于磁场中并通有电流，线圈的两条对边将受到方向相反的两个力，从而产生转动效果（力偶）。
Turning effect = Force × perpendicular distance
转动效果 = 力 × 力的作用线之间的垂直距离
The coil rotates until the plane of the coil is perpendicular to the magnetic field. In a simple DC motor, the split-ring commutator reverses the current every half turn so the coil continues rotating in the same direction.
线圈会一直转动到线圈平面与磁场方向垂直。在简单的直流电动机中，换向器（半环）每半圈改变一次电流方向，从而使线圈沿同一方向持续转动。
5. The Direct Current (DC) Motor | 直流电动机
A DC motor uses the motor effect to convert electrical energy into kinetic energy. Key parts include a coil, a magnet, two brushes and a split-ring commutator.
直流电动机利用电动机效应将电能转化为动能。其关键部件包括线圈、磁铁、两个电刷以及一个换向器（半环形铜片）。
| Part / 部件 | Function / 作用 |
| Coil / 线圈 | Rotates in the magnetic field when current flows. / 电流通过时，在磁场中转动。 |
| Split-ring commutator / 换向器 | Reverses the current every half turn so the coil keeps turning. / 每半圈改变电流方向，使线圈持续转动。 |
| Brushes / 电刷 | Maintain electrical contact between the external circuit and the rotating coil. / 保持外部电路与旋转线圈之间的电接触。 |
| Magnet / 磁铁 | Provides the magnetic field needed for the motor effect. / 提供电动机效应所需的磁场。 |
To increase the speed of the motor, increase the current, use a stronger magnet, or increase the number of turns of the coil.
为了增大电动机的转速，可以增大电流、使用更强的磁铁或增加线圈匝数。
6. Electromagnetic Induction | 电磁感应
When a conductor moves relative to a magnetic field (or when the magnetic field around a stationary conductor changes), a potential difference is induced across the ends of the conductor. This is called electromagnetic induction.
当导体相对于磁场运动（或静止导体周围的磁场发生变化）时，导体两端会感应出电势差，这种现象称为电磁感应。
If the conductor is part of a complete circuit, an induced current is produced. The induced current always opposes the change that caused it (Lenz’s Law).
如果导体连接成闭合回路，则会产生感应电流。感应电流的方向总是阻碍引起它的变化（楞次定律）。
e.m.f. = rate of change of magnetic flux linkage
感应电动势 = 磁通链的变化率
This formula is qualitative; in IGCSE you only need to understand the factors that affect the size of the induced e.m.f.
该公式仅作定性理解；在 IGCSE 中，你只需要掌握影响感应电动势大小的因素。
7. Factors Affecting Induced E.M.F. | 影响感应电动势的因素
The size of the induced e.m.f. can be increased by increasing the speed of movement, using a stronger magnet, increasing the number of turns on the coil, or increasing the area of the coil cutting the field lines.
感应电动势的大小可以通过以下方式增大：增大运动速度、使用更强的磁铁、增加线圈匝数、或增大线圈切割磁感线的有效面积。
| Change / 改变 | Effect on induced e.m.f. / 对感应电动势的影响 |
| Move wire faster / 导线移动更快 | E.m.f. increases / 电动势增大 |
| Stronger magnet / 更强的磁铁 | E.m.f. increases / 电动势增大 |
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