Electromagnetic field theory
It was the scientist Michael Faraday who first studied in detail the phenomena involving the interaction between electricity and magnetism. Amongst his many achievements, he is credited with the construction of the first electric motor and the discovery of both the principle and the method whereby a rotating magnet can be used to create an electric current in a coil of wire (still the basis of modern electricity generating plants).He also observed the way in which iron filings arrange around a magnet. They appear to follow lines of magnetism leading out from one magnetic pole and back to the other pole. He suggested that the effect of a magnet on a wire carrying a current is the result of “lines of force”. Faraday spent the latter part of his life working to devise an experiment that would confirm his theory of electromagnetic fields but without success.
Finally, a Scottish mathematician, James Clerk Maxwell, picked up on Faraday's ideas and was successful in developing a theory of electromagnetism which enabled testable predictions to be made. Inspired by Faraday's lines of force, he developed a model that unified magnetic and electrical forces. Maxwell “unified” the study of electricity and magnetism in four tidy equations. In essence he discovered that electric and magnetic fields were intrinsically related to one another, with or without the presence of a conductive path for electrons to flow. Stated simply Maxwell's discovery was this:-
'A changing electric field produces a perpendicular magnetic field'
and 'A changing magnetic field produces a perpendicular electric field'
Quite interestingly Maxwell predicted that electromagnetism would be propagated through space at a finite rate and was struck by the similarity between the predicted speed of electromagnetism and the speed of light. From this connection sprang the idea that light was an electric phenomenon and the subsequent discovery of radio waves.