Editing Transformer (section)

===Discovery of induction===
[[Image:Induction experiment.png|thumb|Faraday's experiment with induction between coils of wire<ref>{{cite book|url=https://archive.org/details/bub_gb_JzBAAAAAYAAJ| last=Poyser| first=Arthur William|year=1892|title=Magnetism and Electricity: A Manual for Students in Advanced Classes| location=London and New York|publisher= Longmans, Green, & Co.| page= [https://archive.org/details/bub_gb_JzBAAAAAYAAJ/page/n298 285], fig. 248}}</ref>]]

[[Electromagnetic induction]], the principle of the operation of the transformer, was discovered independently by [[Michael Faraday]] in 1831 and [[Joseph Henry]] in 1832.<ref>{{Cite web|url=http://web.hep.uiuc.edu/home/serrede/P435/Lecture_Notes/A_Brief_History_of_Electromagnetism.pdf|title=A Brief History of Electromagnetism}}</ref><ref>{{cite encyclopedia|encyclopedia=Smithsonian Institution Archives|title=Electromagnetism|url=http://siarchives.si.edu/history/exhibits/henry/electromagnetism}}</ref><ref name="MacPhersonRC">{{cite book|first=Ryan C.|last=MacPherson, Ph.D.|title=Joseph Henry: The Rise of an American scientist|url=http://www.ryancmacpherson.com/publications/3-book-reviews/49-joseph-henry-the-rise-of-an-american-scientist.html|access-date=2015-10-28|archive-url=https://web.archive.org/web/20151208121757/http://www.ryancmacpherson.com/publications/3-book-reviews/49-joseph-henry-the-rise-of-an-american-scientist.html|archive-date=2015-12-08|url-status=dead}}</ref><ref name="Guarnieri2013-56">{{harvnb|Guarnieri|2013|pp=56–59}}</ref> 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]]:

:<math> |\mathcal{E}| = \left|{{\mathrm{d}\Phi_\text{B}} \over \mathrm{d}t}\right|,</math>

where <math>|\mathcal{E}|</math> is the magnitude of the EMF in volts and Φ<sub>B</sub> is the magnetic flux through the circuit in [[Weber (unit)|webers]].<ref name="Chow171">{{cite book|url=https://books.google.com/books?id=dpnpMhw1zo8C&pg=PA171|last= Chow|first= Tai L. |year=2006|title=Introduction to Electromagnetic Theory: A Modern Perspective| location=Sudbury, Mass.| publisher=Jones and Bartlett Publishers| page= 171| isbn=978-0-7637-3827-3}}</ref>

Faraday performed early experiments on induction between coils of wire, including winding a pair of coils around an iron ring, thus creating the first [[Toroid (geometry)|toroidal]] closed-core transformer.<ref name="Guarnieri2013-56"/><ref>{{cite journal|last=Faraday|first=Michael|year=1834|title=Experimental Researches on Electricity, 7th Series|author-link=Michael Faraday|journal=Philosophical Transactions of the Royal Society|volume=124|pages=77–122|doi=10.1098/rstl.1834.0008|s2cid=116224057|url=https://archive.org/details/philtrans08694360}}</ref> 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.
[[Image:Induktionsapparat hg.jpg|thumb|left|Induction coil, 1900, Bremerhaven, Germany]]