Exploring Electrical Exploring Electrical TechnologyTechnology

Mid 19Mid 19thth Century Century Developments in theDevelopments in the

““Age of Electricity”Age of Electricity”

Preoccupying QuestionsPreoccupying Questions

If lightning occupied minds of If lightning occupied minds of electrical explorers during the 18electrical explorers during the 18thth century, one issue that still puzzled century, one issue that still puzzled the new mid 19the new mid 19thth century explorers century explorers was how em waves compare to light.was how em waves compare to light.

Success with electric telegraph may Success with electric telegraph may well have stirred such a search. well have stirred such a search.

On the trailOn the trail

KirchhoffKirchhoff• Credited with electric circuit laws that Credited with electric circuit laws that

complemented Ohm’s Law (V=IR)complemented Ohm’s Law (V=IR) Current law based on conservation of chargeCurrent law based on conservation of charge

Voltage law based on conservation of energyVoltage law based on conservation of energy

• In 1857 demonstrated that electric disturbances In 1857 demonstrated that electric disturbances propagate on highly conductive wire propagate on highly conductive wire at the at the speed of lightspeed of light

outin II All the current that goes into a node must come out.

dropssources VV All the voltage drops around a loop equal zero.

On the trailOn the trail

James Clerk MaxwellJames Clerk Maxwell• Brilliant theorist Brilliant theorist • Developed a coherent mathematical Developed a coherent mathematical

treatment of electromagnetism by treatment of electromagnetism by drawing together the work of othersdrawing together the work of others

Faraday: em induction & concept of fluxFaraday: em induction & concept of flux Gauss: law relating sources to e&m fieldsGauss: law relating sources to e&m fields Ampere: law relating current magnetic fieldsAmpere: law relating current magnetic fields Maxwell’s own contribution: a predictionMaxwell’s own contribution: a prediction

Maxwell’s Written ContributionMaxwell’s Written Contribution

2 Publications2 Publications• A Dynamical Theory of the EM FieldA Dynamical Theory of the EM Field (1864)(1864)

Used Faraday’s concept of field as a basisUsed Faraday’s concept of field as a basis Introduced Maxwell’s 4 basic equationsIntroduced Maxwell’s 4 basic equations

• Electricity & MagnetismElectricity & Magnetism (1873) (1873) Contained basic laws of electromagnetismContained basic laws of electromagnetism Predicted phenomena such as radio waves & Predicted phenomena such as radio waves &

light as em waves and described them in light as em waves and described them in great detail great detail

Maxwell’s Unique ContributionMaxwell’s Unique Contribution

Predicted changes (time variation) in Predicted changes (time variation) in Electric fields will produce Magnetic fields Electric fields will produce Magnetic fields even w/out electric currentseven w/out electric currents

0.4.2

.3.1

BD

t

DJH

t

BE

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 ContributionQuality of Maxwell’s Contribution

Classic equations most concise, yet Classic equations most concise, yet coherent treatment of em ever coherent treatment of em ever formulated and have stood without formulated and have stood without major change for over 140 years!major change for over 140 years!

Survived 20Survived 20thth century revolutions of century revolutions of Relativity and Quantum MechanicsRelativity and Quantum Mechanics

Good to 10Good to 10-10-10 cm cm (100x smaller than the atom)(100x smaller than the atom)

Provides a powerful symbolic Provides a powerful symbolic descriptiondescription

Reaction to Maxwell’s TheoryReaction to Maxwell’s Theory

Elegant others of his day did not accept Elegant others of his day did not accept until verified experimentallyuntil verified experimentally

Heinrich Hertz (1886)Heinrich Hertz (1886)• Found em waves (radio waves) travel at the Found em waves (radio waves) travel at the

speed of lightspeed of light• Validated Maxwell’s theory & predictionsValidated Maxwell’s theory & predictions

If Maxwell illustrated magnificence in If Maxwell illustrated magnificence in mathematical formulation, then Edison mathematical formulation, then Edison showed perseverance of trial and error showed perseverance of trial and error method led to successful invention; by method led to successful invention; by 1886 Edison was already 39 years old!1886 Edison was already 39 years old!

Thomas (Alva) EdisonThomas (Alva) Edison

From early years, Edison showed traits From early years, Edison showed traits that later made him famous as a man that later made him famous as a man

Childhood (born in 1847)Childhood (born in 1847)• Like other children, was curiousLike other children, was curious• Unlike others, Al constantly asked questions… Unlike others, Al constantly asked questions…

ones his mother could not begin to ones his mother could not begin to answeranswer

• Often devised his own experimentsOften devised his own experiments• Once sat on a nest of eggs to see if he could Once sat on a nest of eggs to see if he could

hatch them!hatch them!Biographical notes from Experiencing Electricity & Electronics, by Hazen, 1993.

Edison’s School ExperienceEdison’s School Experience

At age 7, non-stop questions didn’t At age 7, non-stop questions didn’t earn him respect of his teachersearn him respect of his teachers

Behavior punished by schoolmaster Behavior punished by schoolmaster with a whipping; he thought Al was with a whipping; he thought Al was “addled” and that would cure him“addled” and that would cure him

Parents pulled him out of public Parents pulled him out of public school and began to home schoolschool and began to home school

Collected almost 100 chemicals to Collected almost 100 chemicals to test every experiment he couldtest every experiment he could

Edison as a YouthEdison as a Youth

At age 12, prepared for economic world by At age 12, prepared for economic world by selling candy, fruit and newspapers to selling candy, fruit and newspapers to passengers of the Grand Trunk Railwaypassengers of the Grand Trunk Railway

Started printing and publishing the Weekly Started printing and publishing the Weekly Herald from the trainHerald from the train

Set up his own chemistry lab in the Set up his own chemistry lab in the baggage car, right on the trainbaggage car, right on the train

Accidentally set baggage car on fire; Accidentally set baggage car on fire; causing the conductor to “box his ears” causing the conductor to “box his ears” and throw him off the train and throw him off the train

Edison’s Later LifeEdison’s Later Life

He became almost completely deaf; He became almost completely deaf; historians disagree on howhistorians disagree on how

From his own perspective, Edison From his own perspective, Edison considered his disability a blessing, since considered his disability a blessing, since he thought it enabled him to shut out the he thought it enabled him to shut out the outside world and concentrate on the work outside world and concentrate on the work of his interestof his interest

Next time: his adult work in more detailNext time: his adult work in more detail