What induction is

In the last section we studied how electricity can make things move. Next we turn to making an electric current with a conductor that moves in a magnetic field.

When a current passes through a conductor placed in a magnetic field, a force acts on the conductor and pushes it to move. Electromagnetic induction is the reverse process: an electromotive force is set up across the ends of a conductor when it moves in a magnetic field.

Electromagnetic induction was first made known to the world by Michael Faraday. In 1831 he put forward an important law about it, Faraday's law.

The magnetic cards used to enter buildings and offices, and the magnetic cards used to pay (credit and debit cards), work by electromagnetic induction. Electrical energy, essential to the modern world, is mostly produced by converting energy from sources such as oil, coal and nuclear energy into electrical energy by electromagnetic induction.

Why this changed the world

Before Faraday, the only steady source of current was a chemical cell, which is expensive and soon runs down. Induction means that anything that can turn a shaft — falling water, steam from burning coal or oil, the wind — can be used to make electricity, by turning coils past magnets. In Sri Lanka, the hydroelectric stations on the Mahaweli and the coal power station at Norochcholai both end in the same machine: a generator that works by electromagnetic induction. The motor of the last pages and the generator of these pages are the same idea run in opposite directions.