Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force exhibits electromagnetic fields such as electric fields, magnetic fields, light, is one of the four fundamental interactions in nature; the other three fundamental interactions are the strong interaction, the weak interaction, gravitation. At high energy the weak force and electromagnetic force are unified as a single electroweak force. Electromagnetic phenomena are defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes both electricity and magnetism as different manifestations of the same phenomenon; the electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. Ordinary matter takes its form as a result of intermolecular forces between individual atoms and molecules in matter, is a manifestation of the electromagnetic force.
Electrons are bound by the electromagnetic force to atomic nuclei, their orbital shapes and their influence on nearby atoms with their electrons is described by quantum mechanics. The electromagnetic force governs all chemical processes, which arise from interactions between the electrons of neighboring atoms. There are numerous mathematical descriptions of the electromagnetic field. In classical electrodynamics, electric fields are described as electric potential and electric current. In Faraday's law, magnetic fields are associated with electromagnetic induction and magnetism, Maxwell's equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents; the theoretical implications of electromagnetism the establishment of the speed of light based on properties of the "medium" of propagation, led to the development of special relativity by Albert Einstein in 1905. Electricity and magnetism were considered to be two separate forces; this view changed, with the publication of James Clerk Maxwell's 1873 A Treatise on Electricity and Magnetism in which the interactions of positive and negative charges were shown to be mediated by one force.
There are four main effects resulting from these interactions, all of which have been demonstrated by experiments: 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. Magnetic poles attract or repel one another in a manner similar to positive and negative charges and always exist as pairs: every north pole is yoked to a south pole. An electric current inside a wire creates a corresponding circumferential magnetic field outside the wire, its direction depends on the direction of the current in the wire. A current is induced in a loop of wire when it is moved toward or away from a magnetic field, or a magnet is moved towards or away from it. While preparing for an evening lecture on 21 April 1820, Hans Christian Ørsted made a surprising observation; as he was setting up his materials, he noticed a compass needle deflected away 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, that it confirmed a direct relationship between electricity and magnetism. At the time of discovery, Ørsted did not suggest any satisfactory explanation of the phenomenon, nor did he try to represent the phenomenon in a mathematical framework. However, three months 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 CGS unit of magnetic induction is named in honor of his contributions to the field of electromagnetism. His findings resulted in intensive research throughout the scientific community in electrodynamics, they influenced French physicist André-Marie Ampère's developments of a single mathematical form to represent the magnetic forces between current-carrying conductors. Ørsted's discovery represented a major step toward a unified concept of energy.
This unification, observed by Michael Faraday, extended by James Clerk Maxwell, reformulated by Oliver Heaviside and Heinrich Hertz, is one of the key accomplishments of 19th century mathematical physics. It has had far-reaching consequences, one of, the understanding of the nature of light. Unlike what was proposed by the electromagnetic theory of that time and other electromagnetic waves are at present seen as taking the form of quantized, self-propagating oscillatory electromagnetic field disturbances called photons. Different frequencies of oscillation give rise to the different forms of electromagnetic radiation, from radio waves at the lowest frequencies, to visible light at intermediate frequencies, to gamma rays at the highest frequencies. Ørsted was not the only person to examine the relationship between magnetism. In 1802, Gian Domenico Romagnosi, an Italian legal scholar, deflected a magnetic needle using a Voltaic pile; the factual setup of the experiment is not clear, so if current flew across the needle or not.
An account of the discovery was published in 1802 in an Italian newspaper, but it was overlooked by the contemporary scientific community, because Romagnosi did not belong to this community. An earlier, neglected, connec
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters are at Broadcasting House in Westminster, it is the world's oldest national broadcasting organisation and the largest broadcaster in the world by number of employees, it employs over 20,950 staff in total. The total number of staff is 35,402 when part-time and fixed-contract staff are included; the BBC is established under a Royal Charter and operates under its Agreement with the Secretary of State for Digital, Culture and Sport. Its work is funded principally by an annual television licence fee, charged to all British households and organisations using any type of equipment to receive or record live television broadcasts and iPlayer catch-up; the fee is set by the British Government, agreed by Parliament, used to fund the BBC's radio, TV, online services covering the nations and regions of the UK. Since 1 April 2014, it has funded the BBC World Service, which broadcasts in 28 languages and provides comprehensive TV, online services in Arabic and Persian.
Around a quarter of BBC revenues come from its commercial arm BBC Studios Ltd, which sells BBC programmes and services internationally and distributes the BBC's international 24-hour English-language news services BBC World News, from BBC.com, provided by BBC Global News Ltd. From its inception, through the Second World War, to the 21st century, the BBC has played a prominent role in British culture, it is known colloquially as "The Beeb", "Auntie", or a combination of both. Britain's first live public broadcast from the Marconi factory in Chelmsford took place in June 1920, it was sponsored by the Daily Mail's Lord Northcliffe and featured the famous Australian soprano Dame Nellie Melba. The Melba broadcast caught the people's imagination and marked a turning point in the British public's attitude to radio. However, this public enthusiasm was not shared in official circles where such broadcasts were held to interfere with important military and civil communications. By late 1920, pressure from these quarters and uneasiness among the staff of the licensing authority, the General Post Office, was sufficient to lead to a ban on further Chelmsford broadcasts.
But by 1922, the GPO had received nearly 100 broadcast licence requests and moved to rescind its ban in the wake of a petition by 63 wireless societies with over 3,000 members. Anxious to avoid the same chaotic expansion experienced in the United States, the GPO proposed that it would issue a single broadcasting licence to a company jointly owned by a consortium of leading wireless receiver manufactures, to be known as the British Broadcasting Company Ltd. John Reith, a Scottish Calvinist, was appointed its General Manager in December 1922 a few weeks after the company made its first official broadcast; the company was to be financed by a royalty on the sale of BBC wireless receiving sets from approved domestic manufacturers. To this day, the BBC aims to follow the Reithian directive to "inform and entertain"; the financial arrangements soon proved inadequate. Set sales were disappointing as amateurs made their own receivers and listeners bought rival unlicensed sets. By mid-1923, discussions between the GPO and the BBC had become deadlocked and the Postmaster-General commissioned a review of broadcasting by the Sykes Committee.
The Committee recommended a short term reorganisation of licence fees with improved enforcement in order to address the BBC's immediate financial distress, an increased share of the licence revenue split between it and the GPO. This was to be followed by a simple 10 shillings licence fee with no royalty once the wireless manufactures protection expired; the BBC's broadcasting monopoly was made explicit for the duration of its current broadcast licence, as was the prohibition on advertising. The BBC was banned from presenting news bulletins before 19.00 and was required to source all news from external wire services. Mid-1925 found the future of broadcasting under further consideration, this time by the Crawford committee. By now, the BBC, under Reith's leadership, had forged a consensus favouring a continuation of the unified broadcasting service, but more money was still required to finance rapid expansion. Wireless manufacturers were anxious to exit the loss making consortium with Reith keen that the BBC be seen as a public service rather than a commercial enterprise.
The recommendations of the Crawford Committee were published in March the following year and were still under consideration by the GPO when the 1926 general strike broke out in May. The strike temporarily interrupted newspaper production, with restrictions on news bulletins waived, the BBC became the primary source of news for the duration of the crisis; the crisis placed the BBC in a delicate position. On one hand Reith was acutely aware that the Government might exercise its right to commandeer the BBC at any time as a mouthpiece of the Government if the BBC were to step out of line, but on the other he was anxious to maintain public trust by appearing to be acting independently; the Government was divided on how to handle the BBC but ended up trusting Reith, whose opposition to the strike mirrored the PM's own. Thus the BBC was granted sufficient leeway to pursue the Government's objectives in a manner of its own choosing; the resulting coverage of both striker and government viewpoints impressed millions of listeners who were unaware that the PM had broadcast to the nation from Reith's home, using one of Reith's sound bites inserted at the last moment
Electronics World is a technical magazine in electronics and RF engineering aimed at professional design engineers. It is produced monthly in print and digital formats; the editorial content of Electronics World covers the full range of electronics and RF industry activities including technology, components, development tools, networking, communications tools and instrumentation. It encompasses a range of issues in the electronics and RF industry, from design through to product implementation; the features are contributed by academics in the electronics industry. The circulation is split between electronic design engineers, senior managers, R&D professionals within areas such as communications, manufacturing and training, IT, power and gas; the Marconi Company published the first issue of the journal The Marconigraph in April 1911. This monthly magazine was the first significant journal dedicated to wireless communication, it circulated among Marconi engineers and operators. In April 1913, after two years and 24 issues, The Marconigraph was superseded by The Wireless World.
An Illustrated Monthly Magazine for all interested in Wireless Telegraphy and Telephony as its first issue was sold on news-stands. Publication of Wireless World continued uninterrupted throughout World War I, from 4 April 1920 publication frequency was increased to fortnightly From 1 April 1922 it became known as The Wireless World and Radio Review following a merger with The Radio Review, a monthly journal that had first been published in London in October 1919. With the same issue, publication frequency of Wireless World became weekly, it was aimed at home constructors, publishing articles on building radio receivers and, after the BBC started regular 405-line TV programmes from Alexandra Palace in 1936, complete details on building your own TV set - including the winding of the high-voltage CRT deflector coils. A similar series was published after 1945 utilising the ubiquitous EF50 RF pentode amplifier valve. With the outbreak of World War II and the expected shortages of paper and other resources, the publication reverted to being monthly, a frequency that it still retains to this day.
The title was changed in September 1984 to Electronics and Wireless World, from January 1996, to Electronics World. A sister publication was Wireless Engineer, more of a learned journal than a popular magazine, featuring high quality, technical articles. In October 1945 Wireless World published what became a famous article by Arthur C. Clarke which foresaw the coming of communications satellites in synchronous orbit around the Earth. Clarke's "Extra Terrestrial Relays" article was credited as the origin of modern satellite communications and of the geostationary earth orbit, sometimes referred to as Clarke's Orbit. In his Wireless World article Clarke suggested that three satellites placed in the equatorial plane orbit at an altitude of 36,000 km, spaced 120 degrees apart, could provide global communications; the altitude is important as here satellites rotate at the same angular velocity as the surface of the Earth, relative to the centre of the Earth, appearing to be fixed at the same point above its surface, hence geostationary.
In 1962 NASA launched the first communications satellite. Telstar 1 lasted only six months, but this paved the way for modern-day communications-there are nearly 900 active satellites in orbit today of which some two-thirds are communications satellites. Clarke's article, "Extra-Terrestrial Relays", was Electronic World' readers most asked for article to re-print in the magazine's centenary edition; the article was featured in the BBC's The Genius of Invention programme broadcast on 7 February 2013. For decades, Wireless World was a place where pioneers in electronic design shared ideas. In 1947-49, it published articles on building what became the famous "Williamson amplifier" by D. T. N Williamson - using a pair of triode-connected KT66 kinkless power tetrodes in push-pull to give 15 watts output. In 1952 it made the first public announcement of the Baxandall tone control circuit, a design now employed in millions of hi-fi systems including amplifiers and effects for musical instruments. In 1955 it published the design of the popular Mullard 5-10 audio amplifier using two EL84 power pentodes in ultra-linear push-pull configuration.
In the 1960s and 1970s there were many further articles on advances in audio and electronic design, notably all-transistor designs including the'Tobey-Dinsdale Amplifier' and the'Linsley Hood' power amplifier. In the December 1975 edition an article described “feed-forward” error correction for audio amplifiers as embodied in the legendary QUAD 405 current dumping power amplifier designed by Peter Walker and M. P. Albinson. In 1975/6 Wireless World published the design of a decoder of broadcast TV Teletext information before the first commercial decoder became available, it published regular columns of brief Circuit Ideas. In the August to December 1967 editions a series, Wireless World Digital Computer by Brian Crank, was published, it described. It was constructed from "reject" transistors, was intended for teaching the basic principles of computer operation. In 1977 a series of articles was published based on the design of the NASCOM 1 computer. In 1979 they published a design by John Adams for a d
Singapore the Republic of Singapore, is an island city-state in Southeast Asia. It lies one degree north of the equator, at the southern tip of the Malay Peninsula, with Indonesia's Riau Islands to the south and Peninsular Malaysia to the north. Singapore's territory consists of one main island along with 62 other islets. Since independence, extensive land reclamation has increased its total size by 23%; the country is known for its transition from a developing to a developed one in a single generation under the leadership of its founder Lee Kuan Yew. In 1819, Sir Stamford Raffles founded colonial Singapore as a trading post of the British East India Company. After the company's collapse in 1858, the islands were ceded to the British Raj as a crown colony. During the Second World War, Singapore was occupied by Japan, it gained independence from the British Empire in 1963 by joining Malaysia along with other former British territories, but separated two years over ideological differences, becoming a sovereign nation in 1965.
After early years of turbulence and despite lacking natural resources and a hinterland, the nation developed as an Asian Tiger economy, based on external trade and its workforce. Singapore is a global hub for education, finance, human capital, logistics, technology, tourism and transport; the city ranks in numerous international rankings, has been recognised as the most "technology-ready" nation, top International-meetings city, city with "best investment potential", world's smartest city, world's safest country, second-most competitive country, third least-corrupt country, third-largest foreign exchange market, third-largest financial centre, third-largest oil refining and trading centre, fifth-most innovative country, the second-busiest container port. The Economist has ranked Singapore as the most expensive city to live in, since 2013, it is identified as a tax haven. Singapore is the only country in Asia with an AAA sovereign rating from all major rating agencies, one of 11 worldwide. Globally, the Port of Singapore and Changi Airport have held the titles of leading "Maritime Capital" and "Best Airport" for consecutive years, while Singapore Airlines is the 2018 "World's Best Airline".
Singapore ranks 9th on the UN Human Development Index with the 3rd highest GDP per capita. It is placed in key social indicators: education, life expectancy, quality of life, personal safety and housing. Although income inequality is high, 90% of homes are owner-occupied. According to the Democracy Index, the country is described as a "flawed democracy"; the city-state is home to 5.6 million residents, 39% of whom are foreign nationals, including permanent residents. There are four official languages: English, Mandarin Chinese, Tamil, its cultural diversity is reflected in major festivals. Pew Research has found. Multiracialism has been enshrined in its constitution since independence, continues to shape national policies in education, politics, among others. Singapore is a unitary parliamentary republic with a Westminster system of unicameral parliamentary government; the People's Action Party has won every election since self-government began in 1959. As one of the five founding members of ASEAN, Singapore is the host of the Asia-Pacific Economic Cooperation Secretariat and Pacific Economic Cooperation Council Secretariat, as well as many international conferences and events.
It is a member of the East Asia Summit, Non-Aligned Movement and the Commonwealth of Nations. The English name of Singapore is an anglicisation of the native Malay name for the country, in turn derived from Sanskrit, hence the customary reference to the nation as the Lion City, its inclusion in many of the nation's symbols. However, it is unlikely that lions lived on the island. There are however other suggestions for the origin of the name and scholars do not believe that the origin of the name is established; the central island has been called Pulau Ujong as far back as the third century CE "island at the end" in Malay. Singapore is referred to as the Garden City for its tree-lined streets and greening efforts since independence, the Little Red Dot for how the island-nation is depicted on many maps of the world and Asia, as a red dot. Singapore is referred to as the "Switzerland of Asia" in 2017 due to its neutrality on international and regional issues; the Greco-Roman astronomer Ptolemy identified a place called Sabana in the general area in the second century, the earliest written record of Singapore occurs in a Chinese account from the third century, describing the island of Pu Luo Chung.
This was itself a transliteration from the Malay name "Pulau Ujong", or "island at the end". The Nagarakretagama, a Javanese epic poem written in 1365, referred to a settlement on the island called Tumasik. In 1299, according to the Malay Annals, the Kingdom of Singapura was founded on the island by Sang Nila Utama. Although the historicity
Système universitaire de documentation
The système universitaire de documentation or SUDOC is a system used by the libraries of French universities and higher education establishments to identify and manage the documents in their possession. The catalog, which contains more than 10 million references, allows students and researcher to search for bibliographical and location information in over 3,400 documentation centers, it is maintained by the Bibliographic Agency for Higher Education. Official website