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Transcript
Upcoming Classes Thursday, Oct. 11th Special: Jeffrey Katzenberg Interview Assignment due: * None Tuesday, Oct. 16th Good Vibrations and Bad Oscillations Assignment due: * Topic & outline of second oral presentation or written paper Jeffrey Katzenberg @ SJSU No lecture on Thursday. Instead, I encourage you to attend the interview of Jeffrey Katzenberg, Head of DreamWorks Animation SKG Studios. Producer for Shrek (I,II,III), Nightmare before Christmas, Chicken Run, and many others. Morris Dailey Auditorium (in Tower Hall) Oct. 11th (Thurs.), 2:00-3:15pm Upcoming Deadlines Thursday, October 11th Outline of second oral presentation or written paper Tuesday, November 6th Second Set of Oral Presentations Second term paper (if not presenting) Oral Presentations (II) The following persons will give oral presentations on Tuesday, November 6th : • Luttrell,Katherine • Macdonald,Keith • McDonald,Kathleen • Mendoza,Jazmin • Nguyen,Jennifer • Nguyen,Linda For everyone else, term paper is due on that date. Extra Credit: SF Museum of Art Visit San Francisco Museum of Modern Art and see Abstract Expressionist paintings. Turn in your ticket receipt ($7 for students). Worth one homework assignment; deadline is Oct. 16th Guardians of the Secret, Jackson Pollock, 1943 Extra Credit: San Jose Ballet See a performance of San Jose Ballet in San Jose Center for Performing Arts (Nov. 15th – 18th ). Turn in your ticket receipt. Worth one homework assignment or three quiz/participation credits. Ramon Moreno in CARMINA BURANA What Not To Do In Class During class please do not: • Surf the web • Fart loudly • Text message All three are equally distracting to me so your cooperation is appreciated. Thank you. Dissecting the iPod WARNING Strong magnets will be passed around the room. Keep these magnets away from (working) iPods and away from laptops (especially my laptop)! Apple iPod Apple announced its first generation iPod in October 2001 as a Maccompatible product with a 5 Gigabyte disk drive that put “1000 songs in your pocket.” This model’s display was black and white and the control wheel physically turned. Price: $399 Current model (as of Fall 2007) is fifth generation; has a color screen, touch sensitive wheel, and hard disk of 160 Gbytes. Price: $349 iPod Nano is similar but with chip memory replacing disk drive; iPod Shuffle is like Nano but without screen. First Generation Fifth Generation Third Generation iPod Dissected LCD Display Battery Front Panel Disk Drive Circuit Board (on rear cover) Fifth Generation iPod components are similar except for front panel buttons iPod Circuit Board The most complex element inside the iPod is the circuit board, which is essentially a small, specialized computer. Explaining the details of how this works would take several semesters, but let’s look at a few basic ideas behind electric circuits. Current Water flows from the reservoir of higher pressure to the reservoir of lower pressure; flow stops when the pressure difference ceases. Water continues to flow because a difference in pressure is maintained with the pump. Electric Current Just as water current is flow of water molecules, electric current is the flow of electric charge. In circuits, electrons make up the flow of charge. ON OFF Electrical Resistance Current depends not only on the voltage but also on the electrical resistance of the conductor. Metals are good electrical conductors due to unbound electrons (they’re good heat conductors for the same reason). Plastics are poor electrical conductors (i.e., insulators). Pattern printed in metal channels the electrical currents in the circuit board. Ohm’s Law Relation between current, voltage, and resistance is Ohm’s law, (Current) = (Voltage) (Resistance) Ampere is unit of current; symbol is A Volt is unit of voltage; symbol is V Ohm is unit of resistance; symbol is Nervous System Nervous systems in animals use electrical currents to signal the contraction and relaxation of muscles. Frog leg jumps when electrical current passes through it. Conduction in Human Heart The most important electrical signal in our body is the periodic signal that contracts and relaxes our heart muscle to pump blood. Without a constant flow of blood the brain can suffer permanent damage. SA AV Electric Shock The damaging effects of shock are the result of current passing through the body. Effects of Electric Shock on Human Body From Ohm's law, current depends on the voltage and on electrical resistance. Current (A) Effect 0.001 Can be felt 0.005 Is painful When dry, skin’s resistance around 100,000 . 0.010 Causes involuntary muscle contractions (spasms) 0.015 Causes loss of muscle control Resistance drops as low as 100 when wet and salty. 0.070 If through the heart, serious disruption; probably fatal if current lasts for more than 1 s Voltage Sources Charges flow only when they are “pushed” or “driven.” A sustained current requires a suitable pumping device to provide a difference in electric potential—a voltage. Aluminum Lemon Copper Simple Chemical Battery Simple Mechanical Generator Chemical Battery Batteries separate positive and negative charges by using a chemical reaction. Chemical potential energy is converted into electrical energy. Rechargeable Battery Eventually the battery’s chemicals are consumed unless the reaction can be reversed by passing a current into the battery. Automobile battery is recharged while the gasoline engine is running since the engine powers a generator that produces a recharging current. Starting the car Engine running iPod Battery The iPod uses a Lithium ion (Li-Ion) battery. Lithium is a light metal with a high charge density. Lithium ion batteries have the advantage of being light weight, rechargeable, loss of charge is slow when not in use, and may be shaped into a flat, compact shape. Direct & Alternating Current Direct current (DC) is current that flows in only one direction. Alternating current (AC) is current that flows back and forth with alternating direction. Ohmic Heating Flowing electrons strike atoms in a conductor, heating the material. Toaster DC vs. AC Easy to produce small DC currents using batteries, which also have low voltages. For major power lines, less ohmic heating if high voltage AC current is used instead of DC. iPod Hard Disk Data is stored by magnetic recording of the platter’s surface. Arm swings across the surface to write on different “tracks.” Motor spins the platter so the arm can reach any point on the disk. Motor Platter Arm Magnetic Forces General observations regarding magnets: Iron (and a few other metals) are ferromagnetic, which means they can become magnetized. Magnets attract ferromagnetic metals. Two magnets can either attract or repel each other depending on poles. Magnetic Poles Cow magnets Two types of magnetic poles: North (N) and South (S) N S As with electric charges, like poles (N&N, S&S) repel and opposites (N&S) attract. Unlike electric charges, cannot have just a North or just a South pole Magnetic poles are not electric charges Magnets N&S on sides Compass needle is magnet Demo: Magnetic Fields Magnetic field points from South to North. Iron filing act as tiny compass needles, outlining magnetic field lines. Magnet Iron filings in clear oil Inside the magnet, field lines go North to South Ferromagnetic Metals Ferromagnetic metals have similar atomic structure. Spin of the electron in these metals produces a net magnetic field Iron, Cobalt, Nickel Demo: Magnetism & Money Most US coins are not made of ferromagnetic materials but many other countries use iron steel in their currency. Some pennies were made of steel during World War II Some Euro coins contain steel Iron is in the ink used in US paper currency to avoid counterfeiting. Buffalo nickels are 25% nickel metal, which is ferromagnetic Magnetizing Iron Magnetic alignment of iron atoms can be induced by an external magnetic field. S N S Strong Magnet Strong Magnet N N Demo: Magnetizing Iron The atoms in iron nails are induced to align by proximity of the strong magnet Each nail becomes itself a magnet, which in turn magnetizes the nail below it, forming a chain. If the strong magnet is removed, most of the alignment is lost so the nails lose most of their magnetization. Electromagnets N Electric current in a coil of wire creates a magnetic field similar to a bar magnet. S Current passing through loops of coiled wire Demo: Electromagnets Electromagnet created by passing current through a coil of wire. Electromagnet is stronger when an iron bar is inserted within the coil. N Wire Coil S Connect to battery or power supply Iron Bar Electromagnetic Induction Voltage is induced whether the magnetic field of a magnet moves near a stationary conductor or the conductor moves in a stationary magnetic field. Demo: Magnet Induces Current Voltage is induced when a magnet moves towards or away from a coil, inducing a current in the coil. Faster the magnet’s motion, the greater the induced current. Magnetic Recording Write data by magnetizing recording media (e.g., video tape, hard disk) using electromagnets. Data is read back using the induced current produced when magnetized media moves past receiver coils (reverse of writing data). Hard disk Electric Generator Electric generator moves a conductor in a magnetic field to produce voltage via electromagnetic induction Demo: Electric Generator Turn the shaft by hand and as the coils pass the magnets a voltage is induced. DC current is generated. DC Output S H A F T Magnet Magnet Coils Induction: No Free Lunch Takes work to turn the generator crank to produce electric current. The faster we turn the crank to produce more current, the more difficult it is to turn. More difficult to push the magnet into a coil with more loops because the magnetic field of each current loop resists the motion of the magnet. Demo: Electric Motor Can create an electrical motor by passing a current through a set of electro-magnets mounted on a rotating shaft. Current out Current in Electro-magnets Electric Motor, Analyzed Electromagnet mounted on a shaft with opposing magnets on each side. Current direction always such that electromagnet is repelled, causing shaft to turn. Current N S Current N S Demo: Generator Becomes Motor Pass a current into the generator and it becomes an electric motor. DC Input Battery Magnet Magnet Rotor Spins iPod Liquid Crystal Display iPod’s display is similar to a flatpanel computer monitor or LCD television. We’ll discuss how this works in a future lecture when we study the properties of light. Next Lecture Katzenberg Interview Remember: Meet in Morris Dailey Auditorium (in Tower Hall) from 2pm to 3:15pm