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Radio is a technology that allows the transmission of signals by modulation of electromagnetic waves with frequencies below those of light.
Radio waves are a form of electromagnetic radiation, and are created whenever a charged object accelerates with a frequency that lies in the radio frequency (RF) portion of the electromagnetic spectrum. This is the range from a few tens of hertz to a few gigahertz. Electromagnetic radiation travels (propagates) by means of oscillating electric and magnetic fields that pass through the air and the vacuum of space equally well, and does not require a medium of transport.
By contrast, other types of electromagnetic radiation, with frequencies above the RF range are gamma rays, X-rays, and infrared, ultraviolet and visible light.
When radio waves pass a wire, their oscillating electric or magnetic field (depending on the shape of the wire) induces an alternating current and voltage in the wire. This can be transformed into audio or other signals that carry information. Although the word 'radio' is used to describe this phenomenon, the transmissions which we know as television, radio, radarThis article is about the device. For the fictional character in M A S H see Corporal Walter (Radar) O'Reilly. antenna (approximately 40m (130ft) in diameter) rotates on a track to observe activities near the horizon. Radar is an acronym for ra dio d etec, and cell phone are all in the class of radio frequency emissions.
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ELF | SLF | ULF | VLF | LF/ LW | MF/ MW | HF/ SW | VHF | UHF | SHF | EHF 3 Hz | 30 Hz | 300 Hz | 3 kHz | 30 kHz | 300 kHz | 3 MHz | 30 MHz | 300 MHz | 3 GHz | 30 GHz | 300 GHz |
The theoretical basis of the propagation of electromagnetic waves was first described in 1873Events The United Kingdom declares war against Ghana's King Kofi KariKari, who was involved in the trading of slaves. The war ended by July and the British established the Gold Coast Colony. January 17 Indian Wars: First Battle of the Stronghold during th by James Clerk MaxwellJames Clerk Maxwell ( June 13, 1831 November 5, 1879) was a Scottish physicist, born in Edinburgh. Maxwell developed a set of equations expressing the basic laws of electricity and magnetism as well as the Maxwell distribution in the kinetic theory of gas in his paper to the Royal SocietyThe Royal Society of London is claimed to be the oldest learned society still in existence and was founded in 1660. The Royal Irish Academy, founded in 1782, is also closely affiliated with it. The Royal Society of Edinburgh (founded 1783) is a separate S A dynamical theory of the electromagnetic field, which followed his work between 18611861 is a common year starting on Tuesday. Events January January 1 Benito Juarez captures Mexico City January 2 Friedrich Wilhelm IV of Prussia dies and is succeeded by Wilhelm I January 3 American Civil War: Delaware votes not to secede from the United and 18651865 is a common year starting on Sunday. Events January 31 American Civil War: Confederate General Robert E. Lee becomes general-in-chief. February 17 American Civil War: Columbia, South Carolina burns as Confederate forces flee from advancing Union forc.
In 1878 David E. HughesHughes ( 1831- 1900) was an accomplished musician and a professor of music as well as chair of natural philosophy at St. Joseph's College in Bardstown, Kentucky. He was also an experimental physicist, mostly in the areas of electricity and signals. He inv was the first to transmit and receive radio waves when he noticed that his induction balanceMetal detectors use electromagnetic induction to detect metal. In 1881, Alexander Graham Bell constructed a crude metal detector in an attempt to find an assassin's bullet in President James Garfield. Gerhard Fischar patented a portable version in 1931. caused noise in the receiver of his homemade telephone. He demonstrated his discovery to the Royal Society in 1880 but was told it was merely induction.
It was Heinrich Rudolf Hertz who, between 1886 and 1888, first validated Maxwell's theory through experiment, demonstrating that radio radiation had all the properties of waves (now called Hertzian waves), and discovering that the electromagnetic equations could be reformulated into a partial differential equation called the wave equation.
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