Propagation of electromagnetic waves When EM waves propagate, they produce oscillating electric and magnetic fields. How did we know this? Is there any experimenting concluding this or it this just a theory?
 A: This is more a question for history of science SE. It was Heinrich Hertz who demonstrated that electromagnetic disturbances travel at the speed of light, as predicted by Maxwell. This was considered proof of Maxwell's identification of light as an electromagnetic wave.
Nowadays all relevant experiments confirm this and this identification is a as close to fact as theory will ever be.
A: The phenomenon you're describing is the end result of millenias of observations. The theory has been developed since ancient culture. One might have observed small particles being attracted to certain substances having been rubbed against wool for example. Then there have been the prolonged use of the compass. Eventually electricity was coined, and someone observed a compass-needle placed next to a current-carrying wire turn. Hertz proposed that electromagnetic fields had frequencies, Ampere (?) discovered that there is a magnetic field assiciated with a current-carrying wire.
Maybe this is not my best written up answer on this website, but the answer would be very detailed and long if it was to be done perfectly. Basically the theory which we use today is the superposition of several theories all having been developed at different times in history, though in greater frequency after 1600s.
