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Electromagnetic Force and Its Manifestations

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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.


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 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.

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.


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 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 Shelley’s Frankenstein




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 electrons Today: Basic unit of matter = atom 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 Inseparable property of certain particles Electrons: negative electric charge Protons: positive electric charge Charge interaction Electric 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 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. This shocking work may account for the look on his face.

25 Measuring electric forces
Coulomb’s law Relationship giving force between two charges Force between two charged objects: repulsive if q1 and q2 are same attractive if q1 q2 different Both objects feel same force 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.

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.

28 The results of the first two steps are shown below
Given: q1 = 1.00 C q2 = 1.00 C d = 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 / d2 Felect = (9.0 x 10^9 N•m2/C2) • (1.00 C) • (1.00 C) / (1.00 m)2 Felect = 9.0 x 10^9

30 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 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 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 Units = ampere, amps (A) Direct current (DC) Charges move in one direction Electronic devices, batteries, solar cells 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
Charge flows easily Many loosely attached electrons are free to move from atom to atom Examples: metals, graphite (carbon) Electrical insulators Charge does not easily flow Electrons are held tightly, electron motions restricted Examples: Glass, wood, diamond (carbon), rubber Semiconductors Conduct/insulate depending on circumstances Applications: Computer chips, solar cells, ...

35 Resistance Resistance factors Type of material Length
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) Circuit elements
Necessary for continuing flow Charge moves out one terminal, through wire and back in the other terminal Circuit elements Charges do work 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 Two sources Collisions with other electrons in current Collisions with other charges in material This is Ohm’s law

39 Electrical power and work
Three circuit elements contribute to work Voltage source Electrical device Conducting wires Power 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 Reaction leaves negative charge on zinc and positive charge on carbon rod Always produces 1.5 volts regardless of size Larger voltages produced by combination of smaller cells (battery)

41 Household Circuits and Safety
Parallel Circuit Current can flow through any branch without first going through any other Circuit breaker (or fuse) Disconnects circuit when a preset value (15 or 20 amps) reached Three-pronged plug Provides grounding wire In case of a short circuit, current will travel through grounding wire to ground Ground-fault interrupter (GFI) Detects difference in load-carrying and system wire If 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 view Associated with magnetic fields Field lines go from north to south poles

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

44 Earth’s magnetic field
Shaped and oriented as if huge bar magnet were inside South pole of magnet near geographic north pole Geographic North Pole and north magnetic pole different Magnetic 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 fields Shape of field determined by geometry of current Straight wire Current loops Solenoid

50 Electromagnetism Solenoid switches Electromagnet
Loops of wire formed into cylindrical coil (solenoid) Current run through coil produces a magnetic field Can be turned on/off by turning current on or off Strength depends on size of current and number of loops Widely used electromagnetic device Solenoid switches Moveable spring-loaded iron core responds to solenoid field Water 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 magnet This rotation moves a pointer on a scale

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

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

54 Transformers Steps AC voltage up or down Two parts
Primary (input) 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 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 More loops in secondary coil – higher voltage output (step-up transformer) Fewer loops in secondary coil – lower voltage output (step-down transformer)

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