Presentation on theme: "Electromagnetic Force and Its Manifestations"— Presentation transcript:
1 Electromagnetic Force and Its Manifestations DSAPhysics
2 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.
3 AmberAmber 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.
5 Greek + Latin = EnglishAncient 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.
6 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.
8 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.
10 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.
11 MusicIn general the term Romanticism when applied to music means the period roughly from the 1820's until 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.
16 Frankenstein 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.
17 The Cow Pock-or-the-Wonderful Effects of the New Inoculation The Cow Pock-or-the-Wonderful Effects of the New Inoculation! James Gillray ( ) Photographic reproduction of an etching appearing in Vide--The Publications of ye Anti-Vaccine Society, June 12, 1802
18 Electric charge Electron theory of charge Today: Ancient mystery: “Amber effect”J. J. Thompson: identified negatively charged electronsToday:Basic unit of matter = atomAtoms made up of electrons and nuclei containing positively charged protons and neutral neutrons (See Ch. 8)
20 Electric charge and electrical forces Charges in matterInseparable property of certain particlesElectrons: negative electric chargeProtons: positive electric chargeCharge interactionElectric force“Like charges repel; unlike charges attract”Ions: non-zero net charge from loss/gain of electrons
21 Electrostatic charge Stationary charge confined to an object Charging mechanismsFrictionContact with a charged object (charge by induction)
23 Measuring 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 electronsElectron charge = 1.60 x CFundamental charge of electron (and proton)Smallest seen in natureAll charged objects have multiples of this charge
24 Charles Augustin Coulomb lived from 1736 to 1806 Charles Coulomb worked on applied mechanics but he is best known for his work on electricity and magnetism.This shockingwork may account forthe look on his face.
25 Measuring electric forces Coulomb’s lawRelationship giving force between two chargesForce between two charged objects:repulsive if q1 and q2 are sameattractive if q1 q2 differentBoth objects feel same forceDistance between objects increases: strength of force decreasesDouble distance, force reduced by 1/4
26 Example ASuppose that two point charges, each with a charge of Coulomb are separated by a distance of 1.00 meter. Determine the magnitude of the electrical force of repulsion between them.
27 Solving the ProblemThe first step of the strategy is the identification and listing of known information in variable form. Here we know the charges of the two objects (q1 and q2) and the separation distance between them (d). The next step of the strategy involves the listing of the unknown (or desired) information in variable form. In this case, the problem requests information about the force. So F is the unknown quantity.
28 The results of the first two steps are shown below Given:q1 = 1.00 Cq2 = 1.00 Cd = 1.00 m Find: Felect = ???
29 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.Felect = k • q1 • q2 / d2Felect = (9.0 x 10^9 N•m2/C2) • (1.00 C) • (1.00 C) / (1.00 m)2Felect = 9.0 x 10^9
30 What does the answer mean? Felect = 9.0 x 10^9This 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 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.
31 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
32 Force fieldsModel of a field considers condition of space around a chargeCharge produces electric fieldVisualized by making map of fieldElectric field lines indicate strength and direction of force the field exerts on field of another chargeField linesPoint outward around positively charged particlesPoint inward around negatively charged particleSpacing shows strengthLines closer; field strongerLines further apart: field weaker
33 Electric Current Flow of charge Current = charge per unit timeUnits = ampere, amps (A)Direct current (DC)Charges move in one directionElectronic devices, batteries, solar cellsAlternating current (AC)Electric field moves back and forth through wireCurrent flows one way then the other with changing fieldI = 1.00 amp
34 Electrical conductors and insulators Charge flows easilyMany loosely attached electrons are free to move from atom to atomExamples: metals, graphite (carbon)Electrical insulatorsCharge does not easily flowElectrons are held tightly, electron motions restrictedExamples: Glass, wood, diamond (carbon), rubberSemiconductorsConduct/insulate depending on circumstancesApplications: Computer chips, solar cells, ...
35 Resistance Resistance factors Type of material Length Conductors have less electrical resistance, insulators have moreLengthLonger the wire, more resistanceCross sectional areaThinner the wire, the more resistanceTemperatureResistance increases with increasing temperature
36 Electric circuits Energy source (battery, generator) Circuit elements Necessary for continuing flowCharge moves out one terminal, through wire and back in the other terminalCircuit elementsCharges do workLight bulbs, run motors, provide heat …
37 Electrons move very slowly in DC circuit. The electric field moves near the speed of light.
38 Electrical resistance Loss of electron current energyTwo sourcesCollisions with other electrons in currentCollisions with other charges in materialThis is Ohm’s law
39 Electrical power and work Three circuit elements contribute to workVoltage sourceElectrical deviceConducting wiresPowerIncludes time factorMeasured in watts (joule/sec)Electric utility chargeCents per kilowatt-hourPower in circuitsElectric bills
40 Dry CellProduces electrical energy from chemical reaction between ammonium chloride and zinc canReaction leaves negative charge on zinc and positive charge on carbon rodAlways produces 1.5 volts regardless of sizeLarger voltages produced by combination of smaller cells (battery)
41 Household Circuits and Safety Parallel CircuitCurrent can flow through any branch without first going through any otherCircuit breaker (or fuse)Disconnects circuit when a preset value (15 or 20 amps) reachedThree-pronged plugProvides grounding wireIn case of a short circuit, current will travel through grounding wire to groundGround-fault interrupter (GFI)Detects difference in load-carrying and system wireIf difference detected, opens circuit within a fraction of second (much quicker than circuit breaker)
42 Magnetism Earliest ideas Modern view Associated with naturally occurring magnetic materials (lodestone, magnetite)Characterized by “poles” - “north seeking” and “south seeking”Other magnetic materials - iron, cobalt, nickel (ferromagnetic)Modern viewAssociated with magnetic fieldsField lines go from north to south poles
43 Magnetic poles and fields Magnetic fields and poles inseparablePoles always come in north/south pairsField lines go from north pole to south poleLike magnetic poles repel; unlike poles attract
44 Earth’s magnetic field Shaped and oriented as if huge bar magnet were insideSouth pole of magnet near geographic north poleGeographic North Pole and north magnetic pole differentMagnetic declination = offset
46 The earth is a ginormous magnet? Yes, it is because of the hot metal that flows deep in the outer core of our planet as the earth spins.
47 Klingon Starship with shields raised against phaser blast from uss enterprise
48 Planet earth with field raised against photon and proton attack by sun Caution: illustration not to scale. Also, the Earth doesn’t really know it’s under attack—the magnetic field just is, but we wouldn’t be here without it.
49 Electric currents and magnetism Moving charges (currents) produce magnetic fieldsShape of field determined by geometry of currentStraight wireCurrent loopsSolenoid
50 Electromagnetism Solenoid switches Electromagnet Loops of wire formed into cylindrical coil (solenoid)Current run through coil produces a magnetic fieldCan be turned on/off by turning current on or offStrength depends on size of current and number of loopsWidely used electromagnetic deviceSolenoid switchesMoveable spring-loaded iron core responds to solenoid fieldWater valves, auto starters, VCR switches, activation of bells and buzzers
51 Galvanometer Measures size of current from size of its magnetic field Coil of wire wrapped around an iron core becomes an electromagnet that rotates in field of a permanent magnetThis rotation moves a pointer on a scale
52 Electromagnetic induction Causes:Relative motion between magnetic fields and conductorsChanging magnetic fields near conductorsDoes not matter which one moves or changesEffect:Induced voltages and currentsSize of induced voltage depends on:Number of loopsStrength of magnetic fieldRate of magnetic field changeDirection of current depends on direction of motion
53 GeneratorsDevice that converts mechanical energy into electrical energyStructureAxle with many loops in a wire coilCoil rotates in a magnetic fieldTurned mechanically to produce electrical energy
54 Transformers Steps AC voltage up or down Two parts Primary (input) coilSecondary (output) coilAC current flows through primary coil, magnetic field grows to maximum size, collapses to zero then grows to maximum size with opposite polarityGrowing and collapsing magnetic field moves across wires in secondary coil, inducing voltageSize of induced voltage proportional to number of wire loops in each coilMore loops in secondary coil – higher voltage output (step-up transformer)Fewer loops in secondary coil – lower voltage output (step-down transformer)