Illustration of Faraday’s law of induction

1831 Faraday’s
law of induction

The book of science

Tom Sharp

Michael Faraday electromagnetism Illustration of Faraday’s law of induction

Faraday’s law of induction

Michael Faraday was the first to discover electromagnetic induction, that a moving magnetic field creates a separation of charge in an electric circuit. Faraday hooked up a voltaic cell to a wire coiled around an iron ring, and a galvanometer to another wire coiled around the other side of the ring. The galvanometer showed a transient current when he connected or disconnected the voltaic cell. Electromagnetic induction is the operating principle of transformers, inductors, motors, and generators.

Separation of charge

Faraday was the first to realize that a changing magnetic field creates electromotive force in an electric circuit. And Faraday was the first to realize that chemical reactions in a voltaic cell provide its electromotive force. Nothing is inherent in electrodes and electrolyte so that contact between them alone could drive an endless electric current, as Alessandro Volta thought. Instead, both battery and moving magnetic field create a separation of electric charge, and charge separation is what we call voltage.

Lines of force

The lines of force around a bar magnet form closed curves, passing out from the north pole and back in to the south pole. You can see these curved lines using iron filings on a surface, although the lines might depend on the iron filings themselves. Maybe the magnetic force radiates perpendicularly across these lines. Nevertheless, the lines pass undiminished through a vacuum, repelling a piece of bismuth in a vacuum tube, just as easily as they pass through the air we breathe, and seem to do so without requiring time in their propagation, which indicates that they are a property of space itself and not a vibration of a supposed aether that might fill space.

Change of flux

Photons travel and electrons spin, bosons combine and fermions exclude, matter has gravity to warp time and space, and magnets cause actions at a distance. The threatening man in the shadow is invisible until he moves. We ourselves are never part of the problem. We have places to go, and things to do.

The volt, our unit of electric potential, has honored Alessandro Volta since 1880; the farad, our unit of electric capacitance, has honored Michael Faraday since 1881. I could go on. One difficulty in the history of science is that even scientists only slowly commonly adopt terms for newly discovered effects and laws (such as volt and farad). Another difficulty is that non-scientists even more slowly adopt the new terms (such as boson and fermion—which also honor scientists).

See also in The book of science:

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