Exploring Electrical Technology Mid 19 th Century Developments in the “Age of Electricity”

Preoccupying Questions  If lightning occupied minds of electrical explorers during the 18 th century, one issue that still puzzled the new mid 19 th century explorers was how em waves compare to light.  Success with electric telegraph may well have stirred such a search.

On the trail  Kirchhoff Credited with electric circuit laws that complemented Ohm’s Law (V=IR)Credited with electric circuit laws that complemented Ohm’s Law (V=IR)  Current law based on conservation of charge  Voltage law based on conservation of energy In 1857 demonstrated that electric disturbances propagate on highly conductive wire at the speed of lightIn 1857 demonstrated that electric disturbances propagate on highly conductive wire at the speed of light All the current that goes into a node must come out. All the voltage drops around a loop equal zero.

On the trail  James Clerk Maxwell Brilliant theoristBrilliant theorist Developed a coherent mathematical treatment of electromagnetism by drawing together the work of othersDeveloped a coherent mathematical treatment of electromagnetism by drawing together the work of others  Faraday: em induction & concept of flux  Gauss: law relating sources to e&m fields  Ampere: law relating current magnetic fields  Maxwell’s own contribution: a prediction

Maxwell’s Written Contribution  2 Publications A Dynamical Theory of the EM Field (1864)A Dynamical Theory of the EM Field (1864)  Used Faraday’s concept of field as a basis  Introduced Maxwell’s 4 basic equations Electricity & Magnetism (1873)Electricity & Magnetism (1873)  Contained basic laws of electromagnetism  Predicted phenomena such as radio waves & light as em waves and described them in great detail

Maxwell’s Unique Contribution  Predicted changes (time variation) in Electric fields will produce Magnetic fields even w/out electric currents A time varying magnetic field generates an electric field (from Faraday’s Law) Either an electric current or a time varying electric field generates a magnetic field An electric field eminates from electric charge density at a point A magnetic monopole cannot be isolated like an electric charge; magnetic field line circulate

Quality of Maxwell’s Contribution  Classic equations most concise, yet coherent treatment of em ever formulated and have stood without major change for over 140 years!  Survived 20 th century revolutions of Relativity and Quantum Mechanics  Good to cm (100x smaller than the atom)  Provides a powerful symbolic description

Reaction to Maxwell’s Theory  Elegant others of his day did not accept until verified experimentally  Heinrich Hertz (1886) Found em waves (radio waves) travel at the speed of lightFound em waves (radio waves) travel at the speed of light Validated Maxwell’s theory & predictionsValidated Maxwell’s theory & predictions  If Maxwell illustrated magnificence in mathematical formulation, then Edison showed perseverance of trial and error method led to successful invention; by 1886 Edison was already 39 years old!

Thomas (Alva) Edison  From early years, Edison showed traits that later made him famous as a man  Childhood (born in 1847) Like other children, was curiousLike other children, was curious Unlike others, Al constantly asked questions… ones his mother could not begin to answerUnlike others, Al constantly asked questions… ones his mother could not begin to answer Often devised his own experimentsOften devised his own experiments Once sat on a nest of eggs to see if he could hatch them!Once sat on a nest of eggs to see if he could hatch them! Biographical notes from Experiencing Electricity & Electronics, by Hazen, 1993.

Edison’s School Experience  At age 7, non-stop questions didn’t earn him respect of his teachers  Behavior punished by schoolmaster with a whipping; he thought Al was “addled” and that would cure him  Parents pulled him out of public school and began to home school  Collected almost 100 chemicals to test every experiment he could

Edison as a Youth  At age 12, prepared for economic world by selling candy, fruit and newspapers to passengers of the Grand Trunk Railway  Started printing and publishing the Weekly Herald from the train  Set up his own chemistry lab in the baggage car, right on the train  Accidentally set baggage car on fire; causing the conductor to “box his ears” and throw him off the train

Edison’s Later Life  He became almost completely deaf; historians disagree on how  From his own perspective, Edison considered his disability a blessing, since he thought it enabled him to shut out the outside world and concentrate on the work of his interest  Next time: his adult work in more detail