Examples of generators of electromotive force.
A variety of voltage sources (clockwise from top left): the Brazos Wind Farm in Fluvanna, Texas (credit: Leaflet, Wikimedia Commons); the Krasnoyarsk Dam in Russia (credit: Alex Polezhaev); a solar farm (credit: U.S. Department of Energy); and a group of nickel metal hydride batteries (credit: Tiaa Monto). The voltage output of each depends on its construction and load, and equals emf only if there is no load.
Source
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"OpenStax College, College Physics. November 3, 2012."
http://cnx.org/content/m42357/latest/?collection=col11406/1.7
OpenStax CNX
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