Electricity Magnetism History of Electricity and Magnetism Static

Electricity & Magnetism

• History of Electricity and Magnetism – Static Electricity – Electrical Power – Laws of Electromagnetism – Induction and Electrical Motors • Electrical Current and Controversy • Maxwell’s Equations

Lightning is a form of static electricity

Early work on static electricity • Leyden Jar • Static Generator

Charles-Augustin de Coulomb’ Law 1736 -1806, France

Luigi Aloisio Galvani Animal electricity 1737 -1771 present-day Italy

Alessandro Giuseppe Antonio Anastasio Volta • Volta 1745 -1827, present-day Italy

André-Marie Ampère • Electromagnetic molecule • Showed that the direction of current determines attraction of parallel wires 1775 -1836, France

Electrical Power SI unit of power is Watt W=V*I 2 W=I *R 2 W = V /R W = Watts V = Volts I = Amps R = Ohms

Ohm’s Law I = current (Amps) V= difference in potential (Volts) R= resistance (Ohms) Georg Simon Ohm 1789 -1854, present-day Germany

Hans Christian Ørsted • Electric current creates a magnetic field 1777 -1851, Denmark

Michael Faraday • Assistant to Humphrey Davy • Chemistry • Electricity and magnetism 1791 -1867, Britain

Faraday Induction Experiment • induction coil (A&B) • Galvanometer

Early Electric Motor Faraday’s electromagnetic rotation experiment (1821) In answer to William Gladstone as to the practical value of electricity, Faraday replied: One day sir, you may tax it.

Faraday electromagnetic field experiment

Electromagnetic Fields • Field eliminates problem of action-at-adistance

AC and DC Current

Circuits in series and parallel Series Parallel

Electric Motors

Tesla and AC Current • Made AC current usable by developing AC motor and generator • Wireless energy Nicola Tesla 1856 (Austrian Empire, Croatia) - 1943 USA (citizen in 1891)

Antagonists in War of the Currents Thomas Alva Edison 1887 – 1931 USA George Westinghouse, Jr. 1846 – 1914 USA

The War of the Currents in 1880’s George Westinghouse Thomas A. Edison • Promoted AC current • Difficult to charge batteries without transformer • Early systems could be used only in series • Early AC motors not practical • More efficient transmission over long distances • Promoted DC current • Could be used to charge batteries directly • Early systems could be used in parallel or series • Low efficiency in long distance transmission • Edison’s disinformation campaign

Willamette Falls and Niagara Falls • Willamette Falls transmission first longdistance transmission (DC). Knocked out by flood and a quick AC replacement was used (1890). • Niagara Falls station, international longdistance transmission. Awarded to Westinghouse (1893).

Magnetic Resonance Imaging • Also called: – Nuclear magnetic resonance imaging – Magnetic resonance tomography

James Clerk Maxwell • Physicist who worked on thermodynamics, optics, and electromagnetism • Unification of optics, electricity, and magnetism by Maxwell's equations – Gauss’s Law for electricity (single electrical charges exist, also Coulomb’s Law) – Gauss’s Law for magnetism (magnetic monopoles do not exist) – Faraday’s Law of induction (a varying magnetic field induces an electrical field) – Ampere’s Law (a varying electrical current –or fields- can create a magnetic field) 1831 -1879, Britain