Title: ELECTROMAGNETIC THEORY
Course: THE MIST€RY OF ELECTRICITY.I > Section: 3. A BRIEF HISTORY OF ELECTROMAGNETIC THEORY (1)

Originally electricity and magnetism were thought of as two separate forces. This view changed when:

While preparing for an evening lecture on 21 April 1820, Hans Christian Oersted made a surprising observation. As he was setting up his materials, he noticed a compass needle deflected from magnetic north when the electric current from the battery he was using was switched on and off. This deflection convinced him that magnetic fields radiate from all sides of a wire carrying an electric current, just as light and heat do, and that it confirmed a direct relationship between electricity and magnetism.

At the time of discovery, Oersted did not suggest any satisfactory explanation of the phenomenon, nor did he try to represent the phenomenon in a mathematical framework. However, three months later he began more intensive investigations. Soon thereafter he published his findings, proving that an electric current produces a magnetic field as it flows through a wire.

The publication of James Clerk Maxwell's 1873 Treatise on Electricity and Magnetism showed the interactions between both, and the main effects resulting from these interactions are:

1. Electric charges attract or repel one another with a force inversely proportional to the square of the distance between them: unlike charges attract, like ones repel.
2. Magnetic poles attract or repel one another in a similar way and always come in pairs: every north pole is yoked to a south pole.
3. An electric current in a wire creates a circular magnetic field around the wire, its direction depending on that of the current.(previous Fig.1 at point 1).
4. A current is induced in a loop of wire when it is moved towards or away from a magnetic field (experience Fig.4), or a magnet is moved towards or away from it (experience 3, 3’), the direction of current depending on that of the movement.