Thursday, 9 July 2009


Although conceived of as distinct phenomena until the 19th century, electricity
and magnetism are now known to be components of the unified theory of
A connection between electricity and magnetism had long been suspected, and in
1820 the Danish physicist Hans Christian Orsted showed that an electric current
flowing in a wire produces its own magnetic field. Andre-Marie Ampere of France
immediately repeated Orsted's experiments and within weeks was able to express
the magnetic forces between current-carrying conductors in a simple and elegant
mathematical form. He also demonstrated that a current flowing in a loop of wire
produces a magnetic dipole indistinguishable at a distance from that produced by a
small permanent magnet; this led Ampere to suggest that magnetism is caused by
currents circulating on a molecular scale, an idea remarkably near the modern
Faraday, in the early 1800's, showed that a changing electric field produces a
magnetic field, and that vice-versus, a changing magnetic field produces an
electric current. An electromagnet is an iron core which enhances the magnetic
field generated by a current flowing through a coil, was invented by William
Sturgeon in England during the mid-1820s. It later became a vital component of
both motors and generators.
The unification of electric and magnetic phenomena in a complete mathematical
theory was the achievement of the Scottish physicist Maxwell (1850's). In a set of
four elegant equations, Maxwell formalized the relationship between electric and
magnetic fields. In addition, he showed that a linear magnetic and electric field
can be self-reinforcing and must move at a particular velocity, the speed of light.
Thus, he concluded that light is energy carried in the form of opposite but
supporting electric and magnetic fields in the shape of waves, i.e. self-propagating
electromagnetic waves.

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