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Transformer
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<p>In <a href="/facts/Electrical_engineering/YYXW1KLW">electrical engineering</a>, a transformer is a <a href="/facts/Passive_component/7oDeoqd3">passive component</a> that transfers <a href="/facts/Electrical_energy/V0pJUrDY">electrical energy</a> from one electrical circuit to another circuit, or multiple <a href="/facts/Electrical_network/zt94kTW0">circuits</a>. A varying current in any coil of the transformer produces a varying <a href="/facts/Magnetic_flux/jQMVxrnD">magnetic flux</a> in the transformer's core, which induces a varying <a href="/facts/Electromotive_force/s6sNaHQL">electromotive force (EMF)</a> across any other coils wound around the same core. Electrical energy can be transferred between separate coils without a metallic (conductive) connection between the two circuits. <a href="/facts/Faraday%27s_law_of_induction/PFBreB0F">Faraday's law of induction</a>, discovered in 1831, describes the induced voltage effect in any coil due to a changing magnetic flux encircled by the coil. </p><p>Transformers are used to change <a href="/facts/Alternating_current/qxICS3xa">AC</a> voltage levels, such transformers being termed step-up or step-down type to increase or decrease voltage level, respectively. Transformers can also be used to provide <a href="/facts/Galvanic_isolation/IMQkwezo">galvanic isolation</a> between circuits as well as to couple stages of signal-processing circuits. Since the invention of the first <a href="/facts/Constant-potential_transformer/RWQATaje">constant-potential transformer</a> in 1885, transformers have become essential for the <a href="/facts/Electric_power_transmission/I9w3lRmM">transmission</a>, <a href="/facts/Electric_power_distribution/F5NfTeWP">distribution</a>, and utilization of alternating current electric power. A wide range of transformer designs is encountered in electronic and electric power applications. Transformers range in size from <a href="/facts/Radio_Frequency/aWku7h4R">RF</a> transformers less than a cubic centimeter in volume, to units weighing hundreds of tons used to interconnect the <a href="/facts/Power_grid/RkWPqjmG">power grid</a>. </p>