Electromagnetic Force and Its Manifestations

DSA Physics

Where Does the Word 'Electricity' Come From?

Electrons, electricity, electronic and other words that begin with "electr..." all originate from the Greek word "elektor," meaning "beaming sun." In Greek, "elektron" is the word for amber.

Amber Amber is a very pretty

goldish brown "stone" that sparkles orange and yellow in sunlight. Amber is actually fossilized tree sap! It's the stuff used in the movie "Jurassic Park." Millions of years ago insects got stuck in the tree sap. Small insects which had bitten the dinosaurs, had blood with DNA from the dinosaurs in the insect's bodies, which were now fossilized in the amber.

Greek + Latin = English

Ancient Greeks discovered that amber behaved oddly - like attracting feathers - when rubbed by fur or other objects. They didn't know what it was that caused this phenomenon. But the Greeks had discovered one of the first examples of static electricity.

The Latin word, electricus, means to "produce from amber by friction."

So, we get our English word electricity from Greek and Latin words that were used in reference to a property/behavior of amber.

19th Century Fascination with Electricity

Romanticism was an artistic and intellectual movement in the history of ideas that originated in late 18th century Western Europe. It stressed strong emotion—which now might include trepidation, awe and horror as aesthetic experiences—the individual imagination as a critical authority—which permitted freedom within or even from classical notions of form in art—and overturning of previous social conventions, particularly the position of the aristocracy. There was a strong element of historical and natural inevitability in its ideas, stressing the importance of "nature" in art and language. Romanticism is also noted for its elevation of the achievements of what it perceived as heroic individuals and artists. It followed the Enlightenment period and was in part inspired by a revolt against aristocratic social and political norms from the previous period, as well as seeing itself as the fulfillment of the promise of that age.

Artists and Writers

In a general sense, "Romanticism" covers a group of related artistic, political, philosophical and social trends arising out of the late 18th and early 19th centuries in Europe. But a precise characterization and a specific description of Romanticism have been objects of intellectual history and literary history for all of the twentieth century without any great measure of consensus emerging. Arthur Lovejoy attempted to demonstrate the difficulty of this problem in his seminal article "On The Discrimination of Romanticisms" in his Essays in the History of Ideas (1948); some scholars see romanticism as completely continuous with the present, some see it as the inaugural moment of modernity, some see it as the beginning of a tradition of resistance to the Enlightenment, and still others date it firmly in the direct aftermath of the French Revolution.

Romanticism is often understood as a set of new cultural and aesthetic values. It might be taken to include the rise of individualism, as seen by the cult of the artistic genius that was a prominent feature in the Romantic worship of Shakespeare and in the poetry of Wordsworth, to take only two examples; a new emphasis on common language and the depiction of apparently everyday experiences; and experimentation with new, non-classical artistic forms.

Romanticism also strongly valued exotic locations and the distant past. Old poetical forms, such as ballads, were revalued, ruins were sentimentalized as iconic of the action of Nature on the works of man, and mythic and legendary material which would previously have been seen as "low" culture became a common basis for works of "high" art and literature.

MusicMusic

In general the term Romanticism when applied to music means the period roughly from the 1820's until 1910. The contemporary application of "romantic" to music did not coincide with modern categories: in 1810, E.T. Hoffman called Mozart, Haydn and Beethoven the three "Romantic Composers", and Ludwig Spohr used the term "good Romantic style" to apply to parts of Beethoven's Fifth Symphony. However, by the early 20th century, the sense that there had been a decisive break with the musical past lead to the establishment of the 19th century as "The Romantic Era", and as such it is referred to in the standard encyclopedias of music.

Mary ShelleyMary Shelley’’s Frankensteins Frankenstein

Frankenstein LivesFrankenstein Lives "They may come up with a disease that can't be

cured, even a monster. Is this the answer to Dr. Frankenstein's dream?"

The time was the early 1970s. The speaker was the mayor of Cambridge, Massachusetts, warning against a proposed DNA laboratory at Harvard University. Today, we almost expect to hear references to "Frankenstein"--whether monster, scientist, novel, film, image, or myth is often unclear--whenever some powerful new technology poses risk to humankind or challenges our ideas of what it means to be human. The atomic bomb, interspecies organ transplants, genetic engineering, and cloning, among many others, have each prompted such warnings; Mary Shelley's hideous brainchild continues to embody and express our fears.

The Cow Pock-or-the-Wonderful Effects of the New Inoculation!

James Gillray (1757-1815)Photographic reproduction of an etching appearing in

Vide--The Publications of ye Anti-Vaccine Society, June 12, 1802

Electric chargeElectric charge Electron theory of chargeElectron theory of charge

Ancient mystery: Ancient mystery: ““Amber Amber effecteffect””

J. J. Thompson: J. J. Thompson: identified negatively identified negatively charged electronscharged electrons

Today:Today: Basic unit of matter = Basic unit of matter =

atomatom Atoms made up of Atoms made up of

electrons and nuclei electrons and nuclei containing positively containing positively charged protons and charged protons and neutral neutrons (See neutral neutrons (See Ch. 8)Ch. 8)

So many ways to draw an atom, So many ways to draw an atom, so little time!so little time!

Electric charge and electrical forcesElectric charge and electrical forces Charges in matterCharges in matter

Inseparable property of Inseparable property of certain particles certain particles

Electrons: negative Electrons: negative electric chargeelectric charge

Protons: positive Protons: positive electric chargeelectric charge

Charge interactionCharge interaction Electric forceElectric force ““Like charges repel; Like charges repel;

unlike charges attractunlike charges attract”” Ions: non-zero net charge Ions: non-zero net charge

from loss/gain of electronsfrom loss/gain of electrons

Electrostatic chargeElectrostatic charge

Stationary charge Stationary charge confined to an objectconfined to an object

Charging Charging mechanismsmechanismsFrictionFrictionContact with a Contact with a

charged object charged object (charge by (charge by induction)induction)

So, the paper gets picked up by the So, the paper gets picked up by the comb, why?comb, why?

Measuring electric chargeMeasuring electric charge

Unit of charge = coulomb (C)Fundamental metric unit (along with m, kg and s)Negative charge of 1 C requires > 6 billion billion

electrons Electron charge = 1.60 x 10-19 C

Fundamental charge of electron (and proton)Smallest seen in natureAll charged objects have multiples of this charge

Charles Augustin Coulomb Charles Augustin Coulomb lived from 1736 to 1806 lived from 1736 to 1806

Charles CoulombCharles Coulomb worked on applied worked on applied mechanics but he is mechanics but he is best known for his best known for his work on electricity and work on electricity and magnetism. magnetism.

This shockingThis shockingwork may account forwork may account forthe look on his face.the look on his face.

Measuring electric forcesMeasuring electric forces

CoulombCoulomb’’s laws law Relationship giving force Relationship giving force

between two chargesbetween two charges Force between two charged Force between two charged

objects: objects: repulsive if qrepulsive if q11 and q and q22 are same are same

attractive if qattractive if q11 q q22 different different

Both objects feel same forceBoth objects feel same force Distance between objects Distance between objects

increases: strength of force increases: strength of force decreasesdecreases Double distance, force reduced by 1/4Double distance, force reduced by 1/4

Example AExample A

Suppose that two point charges, each with Suppose that two point charges, each with a charge of +1.00 Coulomb are separated a charge of +1.00 Coulomb are separated by a distance of 1.00 meter. Determine the by a distance of 1.00 meter. Determine the magnitude of the electrical force of magnitude of the electrical force of repulsion between them.repulsion between them.

Solving the ProblemSolving the ProblemThe first step of the strategy is the The first step of the strategy is the

identification and listing of known information identification and listing of known information in variable form. Here we know the charges in variable form. Here we know the charges of the two objects (q1 and q2) and the of the two objects (q1 and q2) and the separation distance between them (d). The separation distance between them (d). The next step of the strategy involves the listing next step of the strategy involves the listing of the unknown (or desired) information in of the unknown (or desired) information in variable form. In this case, the problem variable form. In this case, the problem requests information about the force. So F is requests information about the force. So F is the unknown quantity. the unknown quantity.

The results of the first two steps are shown below

Given:Given:

q1 = 1.00 C q1 = 1.00 C

q2 = 1.00 Cq2 = 1.00 C

d = 1.00 md = 1.00 m Find: Find: FFelectelect = ???= ???

The final step of the strategy involves substituting known values into the

Coulomb's law equation and using proper algebraic steps to solve for the unknown information. This step is shown below.

FFelectelect = k • q1 • q2 / d = k • q1 • q2 / d22

FFelectelect = (9.0 x 10^9 N•m = (9.0 x 10^9 N•m22/C/C22) • (1.00 C) • ) • (1.00 C) • (1.00 C) / (1.00 m)(1.00 C) / (1.00 m)2 2

FFelectelect = 9.0 x 10^9 = 9.0 x 10^9

What does the answer mean?What does the answer mean?

Felect = 9.0 x 10^9 This answer is what is known in physics circles

as a heck of a big number but how big is this? The force of repulsion of two +1.00-Coulomb

charges held 1.00-meter apart is 9 billion Newtons. This is an incredibly large force which compares in magnitude to the weight of more than 2000 jetliners.

Are such values reality?Are such values reality? This problem was chosen primarily for its conceptual

message. Objects simply do not acquire charges on the order of 1.00 Coulomb. In fact, more likely q values are on the order of 109 or possibly 106 Coulombs. For this reason, a Greek prefix is often used in front of the Coulomb as a unit of charge. Charge is often expressed in units of microCoulomb (µC) and nanoCoulomb (nC). If a problem states the charge in these units, it is advisable to first convert to Coulombs prior to substitution into the Coulomb's law equation. The following unit equivalencies will assist in such conversions.

 1 Coulomb = 106 µC and 1 Coulomb = 109 nC

Force fieldsForce fieldsModel of a field considers

condition of space around a charge

Charge produces electric fieldVisualized by making map of field

Electric field lines indicate strength and direction of force the field exerts on field of another charge

Field lines Point outward around positively charged particlesPoint inward around negatively charged particleSpacing shows strength

Lines closer; field strongerLines further apart: field

weaker

Electric CurrentElectric CurrentFlow of chargeFlow of charge

Current = charge per unit timeCurrent = charge per unit time Units = ampere, amps (A)Units = ampere, amps (A) Direct current (DC)Direct current (DC)

Charges move in one directionCharges move in one direction Electronic devices, batteries, Electronic devices, batteries,

solar cellssolar cells Alternating current (AC)Alternating current (AC)

Electric field moves back and Electric field moves back and forth through wireforth through wire

Current flows one way then the Current flows one way then the other with changing fieldother with changing field

I = 1.00 amp

Electrical conductors and Electrical conductors and insulatorsinsulators

Electrical conductorsElectrical conductors Charge flows easilyCharge flows easily Many loosely attached electrons are free to move Many loosely attached electrons are free to move

from atom to atomfrom atom to atom Examples: metals, graphite (carbon)Examples: metals, graphite (carbon)

Electrical insulatorsElectrical insulators Charge does not easily flowCharge does not easily flow Electrons are held tightly, electron motions Electrons are held tightly, electron motions

restrictedrestricted Examples: Glass, wood, diamond (carbon), Examples: Glass, wood, diamond (carbon),

rubberrubber SemiconductorsSemiconductors

Conduct/insulate depending on circumstancesConduct/insulate depending on circumstances Applications: Computer chips, solar cells, ...Applications: Computer chips, solar cells, ...

ResistanceResistanceResistance factorsResistance factors

Type of materialType of material Conductors have less electrical resistance, insulators have moreConductors have less electrical resistance, insulators have more

LengthLength Longer the wire, more resistanceLonger the wire, more resistance

Cross sectional area Cross sectional area Thinner the wire, the more resistanceThinner the wire, the more resistance

TemperatureTemperature Resistance increases with increasing temperatureResistance increases with increasing temperature

Electric circuitsElectric circuits

Energy source (battery, Energy source (battery, generator)generator)Necessary for Necessary for

continuing flowcontinuing flowCharge moves out one Charge moves out one

terminal, through wire terminal, through wire and back in the other and back in the other terminalterminal

Circuit elementsCircuit elementsCharges do workCharges do work

Light bulbs, run motors, Light bulbs, run motors, provide heat …provide heat …

Electrons move very slowly in DC circuit.

The electric field moves near the speed of light.

Electrical resistanceElectrical resistance

Loss of electron Loss of electron current energycurrent energy

Two sourcesTwo sources Collisions with other Collisions with other

electrons in currentelectrons in current Collisions with other Collisions with other

charges in materialcharges in material

This is This is OhmOhm’’s laws law

Electrical power and workElectrical power and work

Three circuit elements Three circuit elements

contribute to workcontribute to work Voltage sourceVoltage source Electrical deviceElectrical device Conducting wiresConducting wires

Power Power

Includes time factorIncludes time factor

Measured in watts (joule/sec)Measured in watts (joule/sec)

Electric utility chargeElectric utility charge

Cents per kilowatt-hourCents per kilowatt-hour

Power in circuitsPower in circuits

Electric bills Electric bills

Dry CellDry Cell

Produces electrical energy Produces electrical energy from chemical reaction from chemical reaction between ammonium between ammonium chloride and zinc canchloride and zinc can

Reaction leaves negative Reaction leaves negative charge on zinc and positive charge on zinc and positive charge on carbon rodcharge on carbon rod

Always produces 1.5 volts Always produces 1.5 volts regardless of sizeregardless of size Larger voltages produced by Larger voltages produced by

combination of smaller cells combination of smaller cells (battery)(battery)

Household Circuits and SafetyHousehold Circuits and Safety Parallel CircuitParallel Circuit

Current can flow through any Current can flow through any branch without first going through branch without first going through any otherany other

Circuit breaker (or fuse)Circuit breaker (or fuse) Disconnects circuit when a preset Disconnects circuit when a preset

value (15 or 20 amps) reachedvalue (15 or 20 amps) reached Three-pronged plugThree-pronged plug

Provides grounding wireProvides grounding wire In case of a short circuit, current In case of a short circuit, current

will travel through grounding wire will travel through grounding wire to groundto ground

Ground-fault interrupter (GFI)Ground-fault interrupter (GFI) Detects difference in load-Detects difference in load-

carrying and system wirecarrying and system wire If difference detected, opens If difference detected, opens

circuit within a fraction of second circuit within a fraction of second (much quicker than circuit (much quicker than circuit breaker)breaker)

Magnetism Magnetism

Earliest ideasEarliest ideas Associated with naturally occurring magnetic materials Associated with naturally occurring magnetic materials

(lodestone, magnetite)(lodestone, magnetite) Characterized by Characterized by ““polespoles”” - - ““north seekingnorth seeking”” and and ““south south

seekingseeking”” Other magnetic materials - iron, cobalt, nickel Other magnetic materials - iron, cobalt, nickel

(ferromagnetic) (ferromagnetic)

Modern viewModern view Associated with magnetic fieldsAssociated with magnetic fields Field lines go from north to south polesField lines go from north to south poles

Magnetic poles and fieldsMagnetic poles and fields

Magnetic fields and poles Magnetic fields and poles inseparableinseparable

Poles always come in Poles always come in north/south pairsnorth/south pairs

Field lines go from north Field lines go from north pole to south polepole to south pole

Like magnetic poles Like magnetic poles repel; unlike poles attractrepel; unlike poles attract

EarthEarth’’s magnetic fields magnetic field

Shaped and oriented as if Shaped and oriented as if huge bar magnet were insidehuge bar magnet were inside South pole of magnet near South pole of magnet near

geographic north polegeographic north pole

Geographic North Pole and Geographic North Pole and north magnetic pole differentnorth magnetic pole different Magnetic declination = offsetMagnetic declination = offset

The earth is a ginormous magnet?The earth is a ginormous magnet?

Yes, it is because of the hot metal Yes, it is because of the hot metal that flows deep in the outer core that flows deep in the outer core of our planet as the earth spins.of our planet as the earth spins.

Klingon Starship with shields Klingon Starship with shields raised against phaser blast raised against phaser blast

from uss enterprisefrom uss enterprise

Planet earth with field raised Planet earth with field raised against photon and proton against photon and proton

attack by sunattack by sun

Caution: Caution: illustration not to scale. Also, the Earth doesnillustration not to scale. Also, the Earth doesn’’t t really know itreally know it’’s under attack—the magnetic field just is, s under attack—the magnetic field just is, but we wouldnbut we wouldn’’t be here without it.t be here without it.

Electric currents and magnetismElectric currents and magnetism

Moving charges Moving charges (currents) produce (currents) produce magnetic fields magnetic fields

Shape of field Shape of field determined by determined by geometry of currentgeometry of current Straight wireStraight wire Current loopsCurrent loops Solenoid Solenoid

ElectromagnetismElectromagnetism

ElectromagnetElectromagnet Loops of wire formed into cylindrical coil (solenoid)Loops of wire formed into cylindrical coil (solenoid) Current run through coil produces a magnetic fieldCurrent run through coil produces a magnetic field Can be turned on/off by turning current on or offCan be turned on/off by turning current on or off Strength depends on size of current and number of loopsStrength depends on size of current and number of loops Widely used electromagnetic device Widely used electromagnetic device

Solenoid switchesSolenoid switches Moveable spring-loaded iron core responds to solenoid fieldMoveable spring-loaded iron core responds to solenoid field Water valves, auto starters, VCR switches, activation of bells and Water valves, auto starters, VCR switches, activation of bells and

buzzersbuzzers

GalvanometerGalvanometer Measures size of current Measures size of current

from size of its magnetic from size of its magnetic fieldfield

Coil of wire wrapped Coil of wire wrapped around an iron core around an iron core becomes an becomes an electromagnet that electromagnet that rotates in field of a rotates in field of a permanent magnetpermanent magnet

This rotation moves a This rotation moves a pointer on a scalepointer on a scale

Electromagnetic inductionElectromagnetic inductionCauses:Causes: Relative motion between magnetic Relative motion between magnetic

fields and conductorsfields and conductors Changing magnetic fields near Changing magnetic fields near

conductors conductors Does not matter which one moves or Does not matter which one moves or

changeschanges

Effect:Effect: Induced voltages and currentsInduced voltages and currents

Size of induced voltage depends on:Size of induced voltage depends on: Number of loopsNumber of loops Strength of magnetic fieldStrength of magnetic field Rate of magnetic field changeRate of magnetic field change

Direction of current depends on Direction of current depends on direction of motiondirection of motion

Generators Generators

Device that converts mechanical energy Device that converts mechanical energy into electrical energyinto electrical energy

StructureStructureAxle with many loops in a wire coilAxle with many loops in a wire coilCoil rotates in a magnetic fieldCoil rotates in a magnetic field

Turned mechanically to produce electrical Turned mechanically to produce electrical energyenergy

Transformers Transformers Steps AC voltage up or downSteps AC voltage up or down Two partsTwo parts

Primary (input) coilPrimary (input) coil Secondary (output) coilSecondary (output) coil

AC current flows through primary coil, AC current flows through primary coil, magnetic field grows to maximum magnetic field grows to maximum size, collapses to zero then grows to size, collapses to zero then grows to maximum size with opposite polaritymaximum size with opposite polarity

Growing and collapsing magnetic field Growing and collapsing magnetic field moves across wires in secondary coil, moves across wires in secondary coil, inducing voltageinducing voltage

Size of induced voltage proportional to Size of induced voltage proportional to number of wire loops in each coilnumber of wire loops in each coil More loops in secondary coil – higher More loops in secondary coil – higher

voltage output (step-up transformer) voltage output (step-up transformer) Fewer loops in secondary coil – lower Fewer loops in secondary coil – lower

voltage output (step-down transformer)voltage output (step-down transformer)