Mains Electricity | 市电与家庭用电

📚 Mains Electricity | 市电与家庭用电

Mains electricity is the alternating current (AC) supply that powers homes, schools and businesses. In this article, we will explore the nature of mains electricity, the wiring inside a plug, the safety devices that protect us, and the calculations that connect power, current and energy.

市电（家庭用电）是为家庭、学校及商业场所供电的交流电。本文将探讨市电的本质、插头内部的接线、保护我们安全的装置，以及联系功率、电流与电能的计算方法。

1. Alternating Current vs Direct Current | 交流电与直流电

In a direct current (DC) supply, the charge flows continuously in one direction. Batteries and cells produce direct current, and the voltage remains constant with time.

在直流电（DC）电源中，电荷持续沿一个方向流动。电池和电芯产生直流电，其电压随时间保持恒定。

In an alternating current (AC) supply, the direction of the charge flow reverses periodically. The voltage rises and falls, and its polarity swaps at regular intervals. The mains supply is an example of alternating current.

在交流电（AC）电源中，电荷流动方向周期性反转。电压不断升高和降低，其极性按固定时间间隔互换。市电就是交流电的典型例子。

DC: constant voltage → current flows in one direction only

交流电：电压恒定 → 电流仅沿一个方向流动

AC: alternating voltage → current reverses direction periodically

交流电：电压交替变化 → 电流周期性改变方向

The frequency of the UK mains supply is 50 Hz, which means the current completes 50 full cycles every second.

英国市电的频率为50 Hz，这意味着电流每秒完成50个完整周期。

2. The UK Mains Supply | 英国市电规格

In the United Kingdom, the mains electricity supply is rated at 230 V with a frequency of 50 Hz. The live wire alternates between a positive and a negative potential difference relative to the neutral wire at 50 cycles per second.

在英国，市电的额定电压为230 V，频率为50 Hz。火线相对于零线以每秒50个周期的速率在正负电势差之间交替变化。

The stated value of 230 V is the root-mean-square (r.m.s.) value, which represents the equivalent direct voltage that would dissipate the same power in a resistor. The actual peak voltage is considerably higher, around 325 V.

230 V的标注值是均方根（r.m.s.）值，它表示能在电阻上产生相同功率的等效直流电压。实际峰值电压要高得多，约为325 V。

For IGCSE examination purposes, the key fact to remember is simple: the UK mains supply is 230 V alternating current with a frequency of 50 Hz.

就IGCSE考试而言，需要记住的关键事实很简洁：英国市电为230 V交流电，频率为50 Hz。

3. Live, Neutral and Earth Wires | 火线、零线与地线

Every mains circuit has three wires connected to the appliance: the live wire, the neutral wire and, in most cases, the earth wire. Each has a distinct colour and function.

每个市电电路都有三根导线连接到电器：火线、零线，在大多数情况下还有地线。每根导线都有不同的颜色和功能。

The live wire is the most dangerous one. If you touch it, you could become part of the circuit and receive a severe electric shock, because your body provides a path to the ground.

火线是最危险的导线。如果你触碰火线，就可能成为电路的一部分，因身体与大地构成通路而遭受严重电击。

4. Wiring a Three-Pin Plug | 三脚插头的接线

A standard three-pin plug contains three pins: the live pin connected to the brown wire, the neutral pin connected to the blue wire, and the earth pin connected to the green-and-yellow wire. The earth pin is slightly longer than the other two, which ensures that the earth connection is made before the live and neutral connections when the plug is inserted into a socket.

标准三脚插头包含三个引脚：连接棕色导线的火线引脚、连接蓝色导线的零线引脚，以及连接绿

Published by TutorHao | IGCSE Physics Revision Series | aleveler.com

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