<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Electromagnetic induction was discovered by Michael Faraday, published in 1831 . It was discovered independently by Joseph Henry in 1832 . </P> <P> In Faraday's first experimental demonstration (August 29, 1831), he wrapped two wires around opposite sides of an iron ring or "torus" (an arrangement similar to a modern toroidal transformer). Based on his understanding of electromagnets, he expected that, when current started to flow in one wire, a sort of wave would travel through the ring and cause some electrical effect on the opposite side . He plugged one wire into a galvanometer, and watched it as he connected the other wire to a battery . He saw a transient current, which he called a "wave of electricity", when he connected the wire to the battery and another when he disconnected it . This induction was due to the change in magnetic flux that occurred when the battery was connected and disconnected . Within two months, Faraday found several other manifestations of electromagnetic induction . For example, he saw transient currents when he quickly slid a bar magnet in and out of a coil of wires, and he generated a steady (DC) current by rotating a copper disk near the bar magnet with a sliding electrical lead ("Faraday's disk"). </P> <P> Faraday explained electromagnetic induction using a concept he called lines of force . However, scientists at the time widely rejected his theoretical ideas, mainly because they were not formulated mathematically . An exception was James Clerk Maxwell, who used Faraday's ideas as the basis of his quantitative electromagnetic theory . In Maxwell's model, the time varying aspect of electromagnetic induction is expressed as a differential equation, which Oliver Heaviside referred to as Faraday's law even though it is slightly different from Faraday's original formulation and does not describe motional EMF . Heaviside's version (see Maxwell--Faraday equation below) is the form recognized today in the group of equations known as Maxwell's equations . </P>

Which of the pictures shown best represents the phenomenon of induction