page_title: Transformer
section_title: Discovery of induction
hierarchical_section_title: Transformer / History / Discovery of induction
caption_attribution_description: Deutsch: Zur Erzeugung kräftiger Induktionsströme benutzt man Funkeninduktoren; große Geräte wurden nach dem Erfinder auch Rühmkorff genannt. Im Innern befindet sich eine primäre Spule, die aus gut isoliertem dickem Draht gewickelt ist und einen Eisenkern enthält. Sie ist umgeben von der sekundären Spule, die aus sehr vielen, oft mehrere Kilometer langen Wicklungen dünnen Drahtes besteht. Der Strom geht von der Stromquelle zum Stromwender, von dort einerseits zur Primärspule, andererseits zum Wagnerschen Hammer. Wird der Strom eingeschaltet, erzeugt der Wagnersche Hammer fortwährend entstehende und verschwindende Kraftlinien in der Sekundärspule. Die erzeugten Induktionsströme entladen sich als Funken zwischen den Elektroden über dem Gerät. Die Induktionsströme sind Wechselströme da der Öffnungs- und der Schließungsstrom entgegengesetzte Richtung haben. English: Induction coil (also called "spark coil" or "Rühmkorff coil"), used in science education probably around 1900, on display in the Schulhistorische Sammlung (School Historical Museum), Bremerhaven, Germany. It generates high voltage from low voltage direct current (D). Inside the cylinder is the primary winding, consisting of relatively few turns of thick wire, wrapped around an iron core. It can be seen sticking out of both ends of the coil. Around this is wound the secondary winding, consisting of many turns of fine wire. At the left end of the core is a vibrating contact called an "interrupter", which repeatedly breaks the current in the primary circuit to provide the flux changes necessary for induction. When operating, the high voltage from the secondary is applied to the spark gap at the top, creating a stream of sparks
context_page_description: A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple circuits. A varying current in any one coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force across any other coils wound around the same core.
  Electrical energy can be transferred between separate coils without a metallic connection between the two circuits. Faraday's law of induction, discovered in 1831, describes the induced voltage effect in any coil due to a changing magnetic flux encircled by the coil.
  Transformers are most commonly used for increasing low AC voltages at high current or decreasing high AC voltages at low current in electric power applications, and for coupling the stages of signal processing circuits. Transformers can also be used for isolation, where the voltage in equals the voltage out, with separate coils not electrically bonded to one another.
  Since the invention of the first constant-potential transformer in 1885, transformers have become essential for the transmission, distribution, and utilization of alternating current electric power.
context_section_description: Electromagnetic induction, the principle of the operation of the transformer, was discovered independently by Michael Faraday in 1831 and Joseph Henry in 1832. Only Faraday furthered his experiments to the point of working out the equation describing the relationship between EMF and magnetic flux now known as Faraday's law of induction:
  where  is the magnitude of the EMF in volts and ΦB is the magnetic flux through the circuit in webers.
  Faraday performed early experiments on induction between coils of wire, including winding a pair of coils around an iron ring, thus creating the first toroidal closed-core transformer. However he only applied individual pulses of current to his transformer, and never discovered the relation between the turns ratio and EMF in the windings.
caption: Induction coil, 1900, Bremerhaven, Germany
exif: {"Image Make": "LEICA", "Image Model": "DIGILUX 2", "Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS2 Macintosh", "Image DateTime": "2008:08:25 10:59:26", "Image Artist": "No Name", "Image YCbCrPositioning": "Co-sited", "Image PrintIM": "[80, 114, 105, 110, 116, 73, 77, 0, 48, 50, 53, 48, 0, 0, 14, 0, 1, 0, 22, 0, ... ]", "Image ExifOffset": "456", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "1154", "Thumbnail JPEGInterchangeFormatLength": "4591", "EXIF ExposureTime": "2", "EXIF FNumber": "71/10", "EXIF ExposureProgram": "Aperture Priority", "EXIF ISOSpeedRatings": "100", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2008:08:21 10:38:51", "EXIF DateTimeDigitized": "2008:08:21 10:38:51", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "8", "EXIF ShutterSpeedValue": "-1", "EXIF ApertureValue": "57/10", "EXIF ExposureBiasValue": "2", "EXIF MaxApertureValue": "2", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "111/10", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "2460", "EXIF ExifImageLength": "1770", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "EXIF InteroperabilityOffset": "1028", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed", "EXIF CVAPattern": "[0, 2, 0, 2, 0, 1, 1, 2]", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "0", "EXIF FocalLengthIn35mmFilm": "44", "EXIF SceneCaptureType": "Standard", "EXIF GainControl": "None", "EXIF Contrast": "Normal", "EXIF Saturation": "Normal", "EXIF Sharpness": "Normal", "EXIF SubjectDistanceRange": "2"}