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Electromagnetic Force and Its Manifestations DSA Physics.

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1 Electromagnetic Force and Its Manifestations DSA Physics

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 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.

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5 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.

6 19 th 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 emotionwhich now might include trepidation, awe and horror as aesthetic experiencesthe individual imagination as a critical authoritywhich permitted freedom within or even from classical notions of form in artand 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.history of ideas 18th centuryWestern Europe artEnlightenment

7 Artists and Writers

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.intellectual historyliterary historytwentieth centuryArthur Lovejoymodernitythe EnlightenmentFrench Revolution

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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. ShakespeareWordsworth 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.ballads"low" culture"high" art and literature

11 Music In 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.

12 Mary Shelleys Frankenstein

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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! 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 Electron theory of charge Ancient mystery: Amber effect Ancient mystery: Amber effect J. J. Thompson: identified negatively charged electrons J. J. Thompson: identified negatively charged electrons Today: Today: Basic unit of matter = atom Basic unit of matter = atom Atoms made up of electrons and nuclei containing positively charged protons and neutral neutrons (See Ch. 8) Atoms made up of electrons and nuclei containing positively charged protons and neutral neutrons (See Ch. 8)

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

20 Electric charge and electrical forces Charges in matter Charges in matter Inseparable property of certain particles Electrons: negative electric charge Protons: positive electric charge Charge interaction Charge interaction Electric force Like charges repel; unlike charges attract Ions: non-zero net charge from loss/gain of electrons Ions: non-zero net charge from loss/gain of electrons

21 Electrostatic charge Stationary charge confined to an object Stationary charge confined to an object Charging mechanisms Charging mechanisms Friction Contact with a charged object (charge by induction)

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

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 electrons Electron charge = 1.60 x C Fundamental charge of electron (and proton) Smallest seen in nature All 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. Charles Coulomb worked on applied mechanics but he is best known for his work on electricity and magnetism. This shocking This shocking work may account for the look on his face.

25 Measuring electric forces Coulombs law Relationship giving force between two charges Relationship giving force between two charges Force between two charged objects: Force between two charged objects: repulsive if q 1 and q 2 are same attractive if q 1 q 2 different Both objects feel same force Both objects feel same force Distance between objects increases: strength of force decreases Distance between objects increases: strength of force decreases Double distance, force reduced by 1/4

26 Example A Suppose 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. Suppose 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 Problem The 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. The 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: Given: q1 = 1.00 C q1 = 1.00 C q2 = 1.00 C q2 = 1.00 C d = 1.00 mFind: F elect = ??? d = 1.00 mFind: F elect = ???

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. F elect = k q1 q2 / d 2 F elect = k q1 q2 / d 2 F elect = (9.0 x 10^9 Nm 2 /C 2 ) (1.00 C) (1.00 C) / (1.00 m) 2 F elect = (9.0 x 10^9 Nm 2 /C 2 ) (1.00 C) (1.00 C) / (1.00 m) 2 F elect = 9.0 x 10^9 F elect = 9.0 x 10^9

30 What does the answer mean? F elect = 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 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 10 9 or possibly 10 6 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 fields Model of a field considers condition of space around a charge Charge produces electric field Visualized 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 particles Point inward around negatively charged particle Spacing shows strength Lines closer; field stronger Lines further apart: field weaker

33 Electric Current Flow of charge Current = charge per unit time Current = charge per unit time Units = ampere, amps (A) Units = ampere, amps (A) Direct current (DC) Direct current (DC) Charges move in one direction Electronic devices, batteries, solar cells Alternating current (AC) Alternating current (AC) Electric field moves back and forth through wire Current flows one way then the other with changing field I = 1.00 amp

34 Electrical conductors and insulators Electrical conductors Electrical conductors Charge flows easily Charge flows easily Many loosely attached electrons are free to move from atom to atom Many loosely attached electrons are free to move from atom to atom Examples: metals, graphite (carbon) Examples: metals, graphite (carbon) Electrical insulators Electrical insulators Charge does not easily flow Charge does not easily flow Electrons are held tightly, electron motions restricted Electrons are held tightly, electron motions restricted Examples: Glass, wood, diamond (carbon), rubber Examples: Glass, wood, diamond (carbon), rubber Semiconductors Semiconductors Conduct/insulate depending on circumstances Conduct/insulate depending on circumstances Applications: Computer chips, solar cells,... Applications: Computer chips, solar cells,...

35 Resistance Resistance factors Type of material Conductors have less electrical resistance, insulators have more Length Longer the wire, more resistance Cross sectional area Thinner the wire, the more resistance Temperature Resistance increases with increasing temperature

36 Electric circuits Energy source (battery, generator) Energy source (battery, generator) Necessary for continuing flow Necessary for continuing flow Charge moves out one terminal, through wire and back in the other terminal Charge moves out one terminal, through wire and back in the other terminal Circuit elements Circuit elements Charges do work Charges do work Light bulbs, run motors, provide heat … Light 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 energy Loss of electron current energy Two sources Two sources Collisions with other electrons in current Collisions with other electrons in current Collisions with other charges in material Collisions with other charges in material This is Ohms law This is Ohms law

39 Electrical power and work Three circuit elements contribute to work Voltage source Voltage source Electrical device Electrical device Conducting wires Conducting wiresPower Includes time factor Measured in watts (joule/sec) Electric utility charge Cents per kilowatt-hour Power in circuits Electric bills

40 Dry Cell Produces electrical energy from chemical reaction between ammonium chloride and zinc can Produces electrical energy from chemical reaction between ammonium chloride and zinc can Reaction leaves negative charge on zinc and positive charge on carbon rod Reaction leaves negative charge on zinc and positive charge on carbon rod Always produces 1.5 volts regardless of size Always produces 1.5 volts regardless of size Larger voltages produced by combination of smaller cells (battery)

41 Household Circuits and Safety Parallel Circuit Parallel Circuit Current can flow through any branch without first going through any other Current can flow through any branch without first going through any other Circuit breaker (or fuse) Circuit breaker (or fuse) Disconnects circuit when a preset value (15 or 20 amps) reached Disconnects circuit when a preset value (15 or 20 amps) reached Three-pronged plug Three-pronged plug Provides grounding wire Provides grounding wire In case of a short circuit, current will travel through grounding wire to ground In case of a short circuit, current will travel through grounding wire to ground Ground-fault interrupter (GFI) Ground-fault interrupter (GFI) Detects difference in load- carrying and system wire Detects difference in load- carrying and system wire If difference detected, opens circuit within a fraction of second (much quicker than circuit breaker) If difference detected, opens circuit within a fraction of second (much quicker than circuit breaker)

42 Magnetism Earliest ideas Associated with naturally occurring magnetic materials (lodestone, magnetite) Associated with naturally occurring magnetic materials (lodestone, magnetite) Characterized by poles - north seeking and south seeking Characterized by poles - north seeking and south seeking Other magnetic materials - iron, cobalt, nickel (ferromagnetic) Other magnetic materials - iron, cobalt, nickel (ferromagnetic) Modern view Associated with magnetic fields Associated with magnetic fields Field lines go from north to south poles Field lines go from north to south poles

43 Magnetic poles and fields Magnetic fields and poles inseparable Magnetic fields and poles inseparable Poles always come in north/south pairs Poles always come in north/south pairs Field lines go from north pole to south pole Field lines go from north pole to south pole Like magnetic poles repel; unlike poles attract Like magnetic poles repel; unlike poles attract

44 Earths magnetic field Shaped and oriented as if huge bar magnet were inside Shaped and oriented as if huge bar magnet were inside South pole of magnet near geographic north pole South pole of magnet near geographic north pole Geographic North Pole and north magnetic pole different Geographic North Pole and north magnetic pole different Magnetic declination = offset Magnetic declination = offset

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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. 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 doesnt really know its under attackthe magnetic field just is, but we wouldnt be here without it. Caution: illustration not to scale. Also, the Earth doesnt really know its under attackthe magnetic field just is, but we wouldnt be here without it.

49 Electric currents and magnetism Moving charges (currents) produce magnetic fields Moving charges (currents) produce magnetic fields Shape of field determined by geometry of current Shape of field determined by geometry of current Straight wire Straight wire Current loops Current loops Solenoid Solenoid

50 Electromagnetism Electromagnet Loops of wire formed into cylindrical coil (solenoid) Loops of wire formed into cylindrical coil (solenoid) Current run through coil produces a magnetic field Current run through coil produces a magnetic field Can be turned on/off by turning current on or off Can be turned on/off by turning current on or off Strength depends on size of current and number of loops Strength depends on size of current and number of loops Widely used electromagnetic device Widely used electromagnetic device Solenoid switches Moveable spring-loaded iron core responds to solenoid field Moveable spring-loaded iron core responds to solenoid field Water valves, auto starters, VCR switches, activation of bells and buzzers Water valves, auto starters, VCR switches, activation of bells and buzzers

51 Galvanometer Measures size of current from size of its magnetic field 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 magnet Coil of wire wrapped around an iron core becomes an electromagnet that rotates in field of a permanent magnet This rotation moves a pointer on a scale This rotation moves a pointer on a scale

52 Electromagnetic induction Causes: Relative motion between magnetic fields and conductors Relative motion between magnetic fields and conductors Changing magnetic fields near conductors Changing magnetic fields near conductors Does not matter which one moves or changes Does not matter which one moves or changesEffect: Induced voltages and currents Induced voltages and currents Size of induced voltage depends on: Number of loops Number of loops Strength of magnetic field Strength of magnetic field Rate of magnetic field change Rate of magnetic field change Direction of current depends on direction of motion

53 Generators Device that converts mechanical energy into electrical energy Device that converts mechanical energy into electrical energyStructure Axle with many loops in a wire coil Axle with many loops in a wire coil Coil rotates in a magnetic field Coil rotates in a magnetic field Turned mechanically to produce electrical energy Turned mechanically to produce electrical energy

54 Transformers Steps AC voltage up or down Steps AC voltage up or down Two parts Two parts Primary (input) coil Primary (input) coil Secondary (output) coil Secondary (output) coil AC current flows through primary coil, magnetic field grows to maximum size, collapses to zero then grows to maximum size with opposite polarity AC current flows through primary coil, magnetic field grows to maximum size, collapses to zero then grows to maximum size with opposite polarity Growing and collapsing magnetic field moves across wires in secondary coil, inducing voltage Growing and collapsing magnetic field moves across wires in secondary coil, inducing voltage Size of induced voltage proportional to number of wire loops in each coil Size of induced voltage proportional to number of wire loops in each coil More loops in secondary coil – higher voltage output (step-up transformer) More loops in secondary coil – higher voltage output (step-up transformer) Fewer loops in secondary coil – lower voltage output (step-down transformer) Fewer loops in secondary coil – lower voltage output (step-down transformer)


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