History of Electromagnetism

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 Earths magnetic field. Edmond Halleys 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. 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.