📚 Transformers: Voltage and Turns Ratio | 变压器：电压与匝数比
Transformers are essential devices in the electrical power grid. They allow high-voltage transmission over long distances and low-voltage use in homes. For Edexcel IGCSE Science, you need to know the structure, the principle of operation, and the key transformer equation.
变压器是电网中至关重要的设备，既能实现高压远程输电，又能把电压降到家庭用电水平。在爱德思 IGCSE 科学课程中，你需要掌握其结构、工作原理以及核心公式。
1. What Is a Transformer? | 什么是变压器？
A transformer is a device that changes the size of an alternating voltage. It has no moving parts and works by electromagnetic induction.
变压器是一种改变交流电压大小的装置。它没有活动部件，依靠电磁感应工作。
A transformer can increase the voltage.
变压器可以升高电压。
A transformer can decrease the voltage.
变压器也可以降低电压。
The coil connected to the input is called the primary coil.
连接输入端、通入交流电的线圈称为初级线圈。
The coil connected to the output is called the secondary coil.
连接输出端、产生感应电压的线圈称为次级线圈。
2. Why Transformers Only Work with Alternating Current | 为什么变压器只能使用交流电
A transformer needs a changing magnetic field to induce a voltage in the secondary coil. Alternating current changes direction many times per second, so it creates a continuously changing magnetic field.
变压器需要变化的磁场才能在次级线圈中感应出电压。交流电每秒多次改变方向，因此能产生持续变化的磁场。
Direct current flows in one direction and produces a steady magnetic field. A steady field does not induce a continuous voltage in the secondary coil, so a transformer does not work with d.c.
直流电只沿一个方向流动，产生的是恒定磁场。恒定磁场不能在次级线圈中持续感应出电压，所以变压器不能用直流电工作。
3. Structure of a Transformer | 变压器的结构
A simple transformer consists of a primary coil and a secondary coil wound around a soft iron core.
一个简单的变压器由初级线圈、次级线圈和软铁芯组成。
| Component | Function | 作用 |
| Primary coil | The input coil that carries alternating current. | 输入线圈，通入交流电。 |
| Secondary coil | The output coil where induced voltage appears. | 输出线圈，产生感应电压。 |
| Soft iron core | Concentrates and links the magnetic field between the coils. | 集中磁场并把磁场耦合到两个线圈之间。 |
4. How a Transformer Works |
Published by TutorHao | IGCSE Science Revision Series | aleveler.com
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