Exploring Electrical Technology

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

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

3. On the trail • Kirchhoff • 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 light All the current that goes into a node must come out. All the voltage drops around a loop equal zero.

4. On the trail • James Clerk Maxwell • Brilliant theorist • Developed 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

5. Maxwell’s Written Contribution • 2 Publications • 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) • Contained basic laws of electromagnetism • Predicted phenomena such as radio waves & light as em waves and described them in great detail

6. 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 A magnetic monopole cannot be isolated like an electric charge; magnetic field line circulate An electric field eminates from electric charge density at a point

7. 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 20th century revolutions of Relativity and Quantum Mechanics • Good to 10-10 cm (100x smaller than the atom) • Provides a powerful symbolic description

8. 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 light • Validated 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!

9. 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 curious • Unlike others, Al constantly asked questions… ones his mother could not begin to answer • Often devised his own experiments • Once sat on a nest of eggs to see if he could hatch them! Biographical notes from Experiencing Electricity & Electronics, by Hazen, 1993.

10. 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

11. 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

12. 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