📚 Mains Electricity Explained | 市电详解
Mains electricity is the alternating current (ac) supply delivered to homes and businesses. In IGCSE Physics, understanding its features, safety mechanisms, and calculations is essential. This article covers the difference between ac and dc, UK mains specifications, plug wiring, safety devices (fuses, earth wires, circuit breakers, double insulation), power and energy equations, and how to calculate electricity costs.
市电是输送到家庭和企业的交流电。在IGCSE物理中，理解其特性、安全机制和相关计算至关重要。本文将涵盖交流与直流的区别、英国市电规格、插头接线、安全装置（保险丝、地线、断路器和双重绝缘）、功率与能量公式以及电费计算方法。
1. AC vs DC Current | 交流电与直流电流
Electric current can be either direct or alternating. Direct current (dc) flows steadily in one direction, as from a battery. Alternating current (ac) reverses direction periodically. The mains electricity supply delivers ac because it can be easily transformed to high voltages for efficient long-distance transmission and then stepped down for safe home use.
电流可以是直流或交流。直流电（dc）沿一个方向稳定流动，例如来自电池。交流电（ac）周期性地改变方向。市电供应提供交流电，因为它可以方便地升压以实现高效远距离传输，然后再降压以供家庭安全使用。
2. The UK Mains Supply | 英国市电
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