Facts of the Matter: Earth teems with many kinds of electromagnetism

The connection between electricity and magnetism was discovered by accident.

In 1820, Hans Christian Oersted planned to demonstrate the heating of a wire by an electric current, and also to give demonstrations of magnetism, for which he had a compass needle mounted on a wooden stand. He noticed that whenever the current was switched on in the wire, the compass needle moved.

Oddly, the compass needle was neither attracted nor repelled by the wire. Instead, it was perpendicular to the wire and the magnetic influence was circular around the wire, only as long as current flowed through it.

Oersted’s discovery opened up a major field of scientific inquiry that became the subject of study all over Europe.

Michael Faraday, a brilliant English scientist, was part of this effort and in 1821 put it to work to invent electromagnetic rotation, the principle behind the electric motor.

Faraday was working on a number of other projects, and it was 10 years before he could return to the study of electricity and magnetism.

In 1831 he discovered that the magnetism generated by a coil of wire could generate an electric current in another coil, thereby building the first electrical transformer. A few months later he rotated a copper disc between the poles of a horseshoe magnet to generate a continuous direct current. This was the first generator. He had discovered that a changing electric field induces a magnetic field, and a changing magnetic field induces an electric field.

Faraday was not mathematically trained and had difficulty understanding the mathematical musings of Ampere and others who were studying the EM phenomenon.

Instead, he visualized a magnet as if there were lines of magnetic force emanating from it and curving around it to the magnet’s other pole.

He then expressed the electric current induced in the wire in terms of the number of lines of magnetic force that the wire “cut” through.

Most of the mathematical physicists of Europe rejected or openly ridiculed the “lines of force” concept, but it captured the attention of James Clerk Maxwell, a Scottish theoretical physicist.

In 1873 Maxwell published “Treatise on Electricity and Magnetism,” in which he summarized and synthesized the discoveries of Coloumb, Oersted, Ampere, Faraday and others in four equations that are used today as the basis of EM theory.

At the beginning of the treatise Maxwell wrote, “Before I began the study of electricity I resolved to read no mathematics on the subject until I had first read Faraday.”

This was a significant and brilliant move.

Faraday’s work had made little sense to mathematicians who could not visualize those imaginary lines of force. But Maxwell was a skilled and creative mathematician who saw a way to describe the field lines and their changes mathematically.

The equations predicted that a combined electric field and magnetic field could propagate perpendicular to one another through space by a process of mutual induction: A changing magnetic field induces a changing electric field, which induces a changing magnetic field, and so on.

His calculations showed that the mutual induction would have the form of undulations and could only sustain itself if it moved at the speed of light.

In the following decade Heinrich Hertz generated and detected EM waves, which led ultimately to the generation, transmission and proliferation of radio waves.

Today we live in a dense sea of EM radiation of all possible wavelengths, the vast majority of it as undetectable to our naked senses as water is to a fish. Some of them are naturally occurring, and some are man-made, but we are deeply immersed in them.

Some, like sunlight, are intense. Others, like the radio signals exchanged with a spacecraft 10 billion miles from Earth, are infinitesimally small.

Richard Brill is a retired professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.