CHAPTER 16: MAINS ELECTRICITY

How does electricity get from the power station to your home? Why is it dangerous to touch a live wire? How much does it cost to run a 2 kW heater for 5 hours? This chapter answers these questions and more. Mains electricity is the lifeblood of modern society—it powers our homes, industries, and devices. Understanding how it is transmitted, distributed, and used safely is essential knowledge for every citizen and a fundamental part of physics.

16.1 THE NATIONAL GRID: POWER TRANSMISSION

The National Grid is the network of cables and transformers that distributes electricity from power stations to consumers (homes, factories, offices). It covers the entire country, ensuring that electricity is available wherever and whenever it is needed.

16.1.1 The Problem: Power Loss in Cables

When current flows through a transmission line, the cables have resistance. This resistance causes power to be lost as heat, given by the formula:

P_loss = I² × R

Where:

• P_loss = power lost as heat (watts, W)
• I = current flowing through the cable (amperes, A)
• R = resistance of the cable (ohms, Ω)

This power loss is wasted energy—it heats the cables but does no useful work. The goal of power transmission is to minimize this loss.

16.1.2 The Solution: High Voltage Transmission

From the formula P_loss = I²R, we see that power loss depends on the square of the current. If we can reduce the current, we dramatically reduce the loss.

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