Electricity… prior to 18 th -century people experienced static electricity and naturally occurring electricity (lighteni

1. Electricity…prior to 18th-century people experienced static electricity and naturally occurring electricity (lightening) but didn’t understand it. In 1663 a device similar to the Van de Graph generator seen in lab was created.

2. Magnetism…was used in the 12th century when it was discovered that an iron-rich magnetic material would align itself with Polaris (the north star). This mineral, magnetite, was the first compass.

3. The Chinese used a compass around 200 B.C to align buildings for best harmony. • The Chinese are considered the first people to use the compass for navigation in the East and the Venetians were the first to use it in the West. http://www.grand-illusions.com/compass.htm www.aaei.org

4. Electricity • Non-static electricity is the movement of negatively charged particles • Electrons are negatively charged particles • Unlike charges attract, like charges repel

5. Electrons orbiting an atom’s nucleus: http://earthsci.org/education/teacher/basicgeol/miner/miner.html Metals have lots of extra electrons roaming about, so metals are good conductors of electricity.

6. Electrons orbit the nucleus of atoms Each electron has a charge of -1 Holes are where electrons are needed to fill electron shells Electrons want to jump in holes

7. What is a electrical conductor? • A material that allows electrons to flow freely. Most metals are good electrical conductors. Outer electrons are loosely bound to the metal atoms, therefore they can roam freely. • A material that strongly resists the flow of electrons is an insulator. Most non-metals are good insulators.

8. Static Charge When a bunch of negative particles are separated from positive particles (holes), an electrostatic force is created. http://www.tpub.com/neets/book10/39i.htm

9. Electrical forces are much greater than gravitational forces. Gravity is always an attractive force, but electrical forces can be both attractive or repulsive. http://www.glenbrook.k12.il.us/gbssci/phys/Class/estatics/u8l3b.html

10. Electrostatic forces can be stronger than the force of gravity. www.wfu.edu/physics

11. Xerographic Copies use electrostatic charge to produce & transfer images • Photoconductor only conducts charge when exposed to light. • A document image is projected onto a rotating photoconductor drum. An image identical to the original black and white is produced with charged particles. The portions that remain charged are the ‘black’. • Oppositely charged toner adheres to the charged portion of the photoconductor. • A charged piece of paper makes contact with the photoconductor and the toner image is transferred to the paper. • The paper is then heated and the toner is fused onto the paper. http://www.sciam.com/article.cfm?id=how-does-a-photocopier-wo

12. Chester Carlson Physicist, Engineer, & Patent Lawyer • Develops the electrophotography process in 1938 • Acquires patents for the process • Seeks investors from IBM, RCA, General Electric, and the US Army • Finally in 1944 convinces Haloid Co. that idea has commercial viability. • Process is coined XeroX, and Haloid Co. changes its name to Xerox and begins selling copiers in 1950 • Plain Paper copies come out in 1959; sales surge along with Xerox’s revenue

13. Photocopier Process http://www.howstuffworks.com/photocopier1.htm Photocopier Drums are light sensitive. They are made of semiconductor materials. This photoconductive material becomes conductive when in light, but not conductive in the dark. Charge can leave the drum where light hits the drum. Charge remains in the areas where light did not shine. http://www.howstuffworks.com/photocopier1.htm

14. Leyden Jar In 1746 two scientists in Holland experimented with a device that could store charge/electrons. This was the first “capacitor”. By touching the knob with a charged rod, more and more charge could be stored in the Leyden Jar. Homemade jar with tin foil. http://www.alaska.net Wikipedia

15. Ben Franklin’s Kite Experiment Ben Franklin thought the sparks from static electricity looked a lot like lightning. A wire was attached to the kite’s string with a key at the end. The key was attached to a Leyden Jar via a Small wire. It is unlikely Franklin ever did the legendary experiment because two people who tried this experiment died. The installation of Lightening Rods to protect tall buildings came from Franklin.

16. Van De Graph Generator produces static charge

17. Franklin’s Static Electric Motor Electrons hitch-hike on the thimbles to neutralize the + side, thus making the rotor spin around. http://f3wm.free.fr/sciences/jefimenko.html

18. What is electric current?I = charge/time Negatively charged particles called electrons are moving through conductors such as wires. If the electrons flow at a constant rate and always flow in the same direction, we say it is DC (direct current). If the electrons periodically change direction, the current is AC (alternating current). The Physics Classroom

19. Ohm’s Law V = IR V – voltage is electrical force that causes electrons to flow I - Current is the flow rate of electrons R – Resistance to electron flow

20. Current Voltage Henry Cavendish (recall he discovered the constant G) • In 1781 Cavendish discovers electrical potential across a wire with resistance. He discovers that electric current naturally flows from high to low potential and the higher the potential the more current flows. • Georg Ohm publishes the same result plus a complete theory on electricity in 1827. V = IR

21. Current in the Nichrome wire Electrical Energy is converted into light and heat by passing current through a resistive wire.

22. Power Recall James Joule from the famous paddle wheel experiment in the Thermodynamics section. P = V I (watts = Joules/sec) P – Power is the rate of work being done (units are watts, horsepower, etc.) V – Voltage (volts) I – Current (amps) P X time = Energy (KWH, BTU, Joules, Calories)

23. To perform work, a continuous flow of charge is required • Charge is expressed in Coulombs • Current  Coulombs/second • Amp = 1 Coulomb/second Some kind of device or system was needed to produce a continuous flow of charge.

24. Meanwhile…. Luigi Galvani’s conducts experiments with “animal electricity” using frogs’ legs Applying static electricity to dissected frogs’ legs caused the legs to twitch. (c. 1780) Galvani later laid frog legs out on brass hooks that were hooked onto an iron lattice during a thunderstorm. The frog legs continued to twitch after the storm. Alessandro Volta hypothesized that the twitching might be electricity caused by the two different metals (brass and iron).

25. Galvani hanging frog legs on brass hooks. www.hgs.k12.va.us Two metals causing legs To twitch. www.karisteeves.net Luigi Galvani http://itp.nyu.edu

26. Alessandro Volta and the Battery A battery using copper and zinc, interleaved with cardboard soaked in brine (a good electrical conductor). Volta presented in 1800 the world’s first device that could deliver continuous current. Wikipedia An accomplishment that took 50 years, lots of experimentation, and luck too. http://ieee-virtual-museum.org

27. An electrochemical cell has three main parts: two dissimilar metals and an electrolyte. The electrolyte allows ions and electrons to move between the two metals. By creating a closed path, electrons will flow and electricity can be delivered to a device. http://sxxz.blogspot.com

28. The Carbon and Zinc dry-cell battery First demonstrated in 1866. This is a chemical reaction where electrons are exchanged between two metals, causing continuous current through a load. This is a form of chemical energy. Wikipedia

29. Battery Reactions • Sulfuric Acid reacts with Zinc, producing positive zinc ions and electrons. • Attaching a load (motor, light bulb, etc.) between the zinc and the graphite (carbon) allows the electrons to flow to the carbon side where the electrons join with H+ ions. http://en.wikipedia.org/wiki/Zinc-carbon_battery

30. Lead Acid Battery Reactions Pb + SO4²¯ → PbSO4 + 2e- + H+The reduction potential of this reaction is +0.356 Volts. PbO2 + SO4²¯ + 4 H+ + 2e- → PbSO4 + H2OThe potential of this reaction is 1.685 volts. Total voltage created is about 2V. Lead Acid batteries provide high current, and are rechargeable, making them effective for starting cars. http://sxxz.blogspot.com/2005/03/how-do-batteries-work.html

31. An auspicious moment in 1820… Hans Christian Oersted, a Danish Physics professor, was demonstrating electricity when he noticed that whenever the battery was connected such that current flowed in a wire, a nearby compass needle would twitch!!! Oersted by accident discovered that electricity and magnetism are related. His experiment showed that current in a wire has a magnetic field around it.

32. Current in wire Compass http://www.gcse.com

34. Electromagnets in Industrial Applications istockphoto http://www.storchmagnetics.com

35. Michael Faraday Faraday was a self-taught scientist fascinated with science. In 1831 he showed the reverse of Oersted’s experiment: That electricity is created in a wire when the wire is moved through a magnetic field. This is called Electromagnetic Induction

36. www.physics.uiowa.edu

37. Faraday’s Generator Faraday demonstrated that rotational energy could be converted into electrical energy. This was the first generator. It delivered continuous current. http://www.powerstandards.com

38. Faraday demonstrates the Transformer Two coils very close together. Current in the first coil, sets up a magnetic field. This magnetic field induces current in the second coil. The transformer allows the stepping up or down of current based on the ratio of windings in the first coil to the second coil. If current goes up, voltage steps down. If current steps down, voltage steps up. Wikipedia

39. Steam Powered Generators By the 1850’s coal was burned to make steam which in turn was used to turn a generator to produce continuous current. Electricity meant instant, on demand clean power (never mind the coal burning in the next building).

40. http://sol.sci.uop.edu

41. Thomas Edison was determined to provide electricity to light homes. Edison was convinced that electricity should be DC (direct current). DC voltage can not be easily stepped up to high voltages/low current, therefore it was impractical for supplying electricity over long distances.

42. DC makes an attempt… In the 1880’s there were a few DC power stations in England

43. Nikola Tesla invented the Generator/Dynamo in 1880’s Current alternates http://www.physchem.co.za

44. AC wins by the 1890’s AC power stations that generate power at 10,000 volts are built. The voltage is stepped down using transformers. This is similar to today’s technology. http://www.energymanagertraining.com Oregon Historical Society

45. Power Grid is based on AC voltageThis allows stepping up and stepping down of voltage using transformers. http://www.windows.ucar.edu

46. Maxwell’s Equations James Clerk Maxwell took Faraday’s discoveries and put them into equations. The four equations state: 1. Like charges repel, unlike charges attract 2. Magnetic fields always have two poles (positive and negative) 3. A moving/changing magnetic field can produce current. 4. Moving electrical charge (current) can produce a magnetic field.

47. From the Generator we get the Motor The current direction in the wires changes with every half rotation. This electromagnetic has a constantly changing magnetic field, causing the coil to continue to realign inside with the permanent magnet (the stator). This makes the rotor spin. Wikipedia

48. Maxwell predicts Electromagnetic Radiation An electromagnetic wave exists when the changing magnetic field causes an electric field which then causes another changing magnetic field, and so on forever. These oscillating fields together form an electromagnetic wave. An electromagnetic wave will travel and continue on forever until absorbed. Wikipedia.com

49. Heinrich Hertz demonstrates in 1888 the existence of electromagnetic radiation

50. Physical Contact does not need to be made to measure electric or magnetic fields. An electric field exerts a force on charged objects. A magnetic field exerts a force on moving charge. All the magnetic fields we experience are the result of moving charges. Electromagnets make magnetic fields with current in wires. Permanent magnets produce magnetic fields through the orientation of the electron orbits and spins of the atoms in the magnet. Arthur Smith