History of Electromagnetism

The innovations of Andre Marie Ampere and Hans Christian Oersted.

Edmond Halley
Edmond Halley.

Electromagnetism is an area of physics which involves the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force usually produces electromagnetic fields, such as electric fields, magnetic fields and light. The electromagnetic force is one of the four fundamental interactions (commonly called forces) in nature.

The other three fundamental interactions are the strong interaction, the weak interaction and gravitation.

Until 1820, the only magnetism known was that of iron magnets and of "lodestones", natural magnets of iron-rich ore. It was believed that the inside of the Earth was magnetized in the same fashion, and scientists were greatly puzzled when they found that the direction of the compass needle at any place slowly shifted, decade by decade, suggesting a slow variation of the Earth's magnetic field.

Edmond Halley's Theories

How can an iron magnet produce such changes? Edmond Halley (of comet fame) ingeniously proposed that the Earth contained a number of spherical shells, one inside the other, each magnetized differently, each slowly rotating in relation to the others.

Hans Christian Oersted - Electromagnetism Experiments

Hans Christian Oersted was a professor of science at Copenhagen University.

In 1820 he arranged in his home a science demonstration to friends and students. He planned to demonstrate the heating of a wire by an electric current, and also to carry out demonstrations of magnetism, for which he provided a compass needle mounted on a wooden stand.

While performing his electric demonstration, Oersted noted to his surprise that every time the electric current was switched on, the compass needle moved.

He kept quiet and finished the demonstrations, but in the months that followed worked hard trying to make sense out of the new phenomenon.

However, Oersted could not explain why. The needle was neither attracted to the wire nor repelled from it. Instead, it tended to stand at right angles. In the end, he published his findings without any explanation.

Repeat Hans Christian Oersted's Experiment with Magnetic Fields
 

Andre Marie Ampere and Electromagnetism

Andre Marie Ampere in France felt that if a current in a wire exerted a magnetic force on a compass needle, two such wires also should interact magnetically. In a series of ingenious experiments Andre Marie Ampere showed that this interaction was simple and fundamental - parallel (straight) currents attract, anti-parallel currents repel. The force between two long straight parallel currents was inversely proportional to the distance between them and proportional to the intensity of the current flowing in each.

There thus existed two kinds of forces associated with electricity--electric and magnetic. In 1864, James Clerk Maxwell demonstrated a subtle connection between the two types of force, unexpectedly involving the velocity of light.

From this connection sprang the idea that light was an electric phenomenon, the discovery of radio waves, the theory of relativity and a great deal of present-day physics.

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