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cours-analyse numerique

Series-Analyse

The picture is showing the invention of an AM radio.

Radio is the transmission of signals, by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space. Information is carried by systematically changing (modulating) some property of the radiated waves, such as amplitude, frequency, or phase. When radio waves pass an electrical conductor, the oscillating fields induce an alternating current in the conductor. This can be detected and transformed into sound or other signals that carry information.

The meaning and usage of the word “radio” has developed in parallel with developments within the field and can be seen to have three distinct phases: electromagnetic waves and experimentation; wireless communication and technical development; and radio broadcasting and commercialization. Many, many individuals — inventors, engineers, developers, businessmen — contributed to produce the modern idea of radio and thus the origins and ‘invention’ are multiple and controversial.

James Clerk Maxwell, a Scottish scientist, developed the theoretical basis for explaining electromagnetism. He predicted that electric and magnetic fields can couple together to form electromagnetic waves. Heinrich Hertz, a German scientist, is credited with being the first to produce and detect such waves at radio frequencies, in 1888, using a sparkgap transmitter in the Ultra High Frequency range.

In 1893, Nikola Tesla, in America, first demonstrated the principles of wireless communications.Tesla would later ultimately hold the patent rights in the United States. Physicists and inventors such as John Stone Stone and Alexander Stepanovich Popov have cited Tesla as the originator of wireless communications.In August 1894, Oliver Lodge, an English physicist and writer, transmitted radio signals at a meeting of the British Association for the Advancement of Science at the University of Oxford.That same year, Jagadish Chandra Bose, a Bengali Indian physicist, ignited gunpowder and rang a bell at a distance using electromagnetic waves, showing independently that communication signals can be sent without using wires. In 1895, Guglielmo Marconi, an Italian inventor, began experimenting with wireless and went on to develop the world’s first commercial system of radio communication. In 1896, Marconi was granted the world’s first wireless telegraphy patent by the British Patent Office. Marconi has been generally credited with the development of radio by most scholars and historians. In 1909, Marconi was jointly awarded the Nobel Prize for Physics with Karl Ferdinand Braun “in recognition of their contributions to the development of wireless telegraphy.”