# Physics 10 Dates for Electromagnetism

## Professor: George Smoot

## Approximate Dates of Some important Observations, Experiments and Theories,

Ancient times: Knowledge that there are some effects

~~~~~~ - amber rubbed with fur attracts bits of dust and yarn

~~~~~~ - static electricity - spakes on cold, dry days, lightening

~~~~~~ - lode stone compass

1600: Willim Gilbert, an English Scientist, publishes "De Magnete"

1700: Lectures and Demos with electricity to attract and entertain audiences

1747: Ben Franklin (1706-1790)

~~~~~~ - two kinds of charges: positive and negative

~~~~~~ - Like charges repel, unlike charges attract

~~~~~~ - Conservation of Charge: An isolated system has constant total charge.

1785: Charles Austin de Coulomb (1736-1806)

~~~~~~ Coulomb's Law F = k Q1 Q2 / r^2 ~~~~~~ k = 9 x 10^9 N-m^2/c^2

~~~~~~ the force between two charges Q1 and Q2 is proportional to their product divided by the separation distance r squared. Inverse square law.

1780: Luigi Galvani (1737-1790) discovers electricty from two different metals causes frog legs to twitch

1790: Alessandro Volta (1745-1827) finds chemistry acting on two dissimilar metals generates electricity. He invents the voltaic pile - the battery.

1820: Hans Christian Oersted (1777-1851) electric current affects compass needle

~~~~~ Andre Marie Ampere (1775-1836) in Paris finds that wires carrying current produce forces on each other.

~~~~~ Michael Faraday (1791-1867) at Royal Society in London develops idea of electric field and studies the effect of currents on magnets and magnets inducing electric currents

1860: James Clerk Maxwell (1831-1879), a Scottish physicist and mathematician, puts the theory of electromagnetism on mathematical basis

1873: Maxwell publishes "Treatise on Electricity and Magnetism" in which he summarizes and synthesizes the discoveries of Coloumb, Oersted, Ampere, Faraday, et. al. in four mathematical equations. * Maxwell's Equations * are used today as the basis of * electromagnetic theory*. Maxwell makes a prediction about the connections of magnetism and electricity leading directly to the prediction of electromagnetic waves.

1885: Heinrich Hertz () shows Maxwell was correct and generates and detects electromagnetic waves.

1895: Guglielmo Marconi puts the discovery to practical use by sending messages over long distances by means of radio signals. i.e. the "Wireless".

See Discovery Timeline picture or
Discovery Timeline postscript file for printing
to trace the development of electromagnetic work and especially electromagnetic waves from an abstract mathematical curiosity studied in a University to a major driving factor in human society.