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# Electricity653

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Basic powerpoint studying static electricity, electric current, transformers, and magnets

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### Electricity653

1. 1. Electricity
2. 2. Static electricity <ul><li>The buildup of electric charges on an object </li></ul>
3. 3. <ul><li>Negative charge </li></ul><ul><li>Rub a rubber rod with wool </li></ul><ul><li>Rod collects electrons </li></ul><ul><li>Positive charge </li></ul><ul><li>Rub a glass rod with silk </li></ul><ul><li>Rod loses electrons </li></ul>
4. 4. <ul><li>Bubble demo </li></ul><ul><li>Why did this happen? </li></ul><ul><li>Induced charge: </li></ul><ul><li>When one object makes a nearby neutral object act like it has a charge. </li></ul><ul><li>electric dipole </li></ul><ul><li>Any object with different charges on each end. </li></ul>Boab24's
5. 5. <ul><li>Build an electroscope . </li></ul><ul><li>1. Bring your balloon near the aluminum foil, what happens to your leaves? Why? </li></ul>
6. 6. <ul><li>2. Touch your balloon to your aluminum foil ball, what happens to the leaves, why </li></ul><ul><li>This is called conduction </li></ul>
7. 7. <ul><li>3. While the leaves are apart touch your finger to the aluminum foil ball, what happens to the leaves? </li></ul><ul><li>This is called grounding </li></ul>
8. 8. <ul><li>4. Now bring the balloon close to the electroscope so the leaves spread but not too close where conduction happens. While the leaves are spread keep the balloon where it is and touch the foil. Now take the balloon and your finger away. Why does the electroscope stay spread? </li></ul>
9. 9. <ul><li>5. Before grounding your electroscope, bring your balloon close to it again, what happens to the leaves? Why? </li></ul>
10. 10. 2 laws <ul><li>Law of electric charges </li></ul><ul><li>Like repel, unlike attract </li></ul><ul><li>Coulombs law: </li></ul><ul><li>The force between two charged objects is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. </li></ul><ul><li>F=k(q 1 q 2 )/r 2 </li></ul><ul><li>Rough translation: the closer two charged objects are, the stronger the force between them. </li></ul>
11. 11. Magnets <ul><li>Anything with a north and south pole </li></ul><ul><li>2 types of magnets </li></ul><ul><li>Permanent </li></ul><ul><li>Temporary </li></ul><ul><li>Magnetic field </li></ul><ul><li>Area around a magnet where the magnetic force can be felt </li></ul>
12. 12. <ul><li>Who discovered magnets? </li></ul><ul><li>Greeks </li></ul><ul><li>They called it lodestone because it always pointed to the lodestar or North Star </li></ul>
13. 13. How Magnets work <ul><li>All atoms have electrons </li></ul><ul><li>Electrons spin making a magnetic field </li></ul><ul><li>Clockwise = North pole on top </li></ul><ul><li>Counterclockwise = North pole on bottom </li></ul><ul><li>Atoms with pairs of electrons cancel each other out </li></ul>
14. 14. <ul><li>Good magnets are made mostly out of odd numbered elements </li></ul><ul><li>Atoms with magnetic poles gather into domains </li></ul><ul><li>If we can get domains to line up we have a magnet </li></ul>
15. 15. <ul><li>2 ways </li></ul><ul><li>Run electricity around ferromagnetic material </li></ul><ul><li>Rub with a magnet </li></ul>
16. 16. The Earth as a magnet <ul><li>Compasses are little magnets </li></ul><ul><li>When the north pole points north it is actually pointing to the south (magnetic) pole of the earth </li></ul><ul><li>Earth’s poles flip every 50,000 years </li></ul>
17. 17. Cirque de circuits <ul><li>Electric circuits: </li></ul><ul><li>Path that electrons can take </li></ul>Dude tests electric shock collar on himself Dude 2 charges himself with cathode ray tube and touches stuff
18. 18. Volts (E) <ul><li>Potential difference </li></ul><ul><li>How bad the – wants to give electrons and the + wants them </li></ul>
19. 19. Amps (I) <ul><li>How many electrons pass a point in 1 second </li></ul><ul><li>1 amp = 6.25 x 10 18 electrons </li></ul>
20. 20. Ohms (R) <ul><li>Resistance to electron flow </li></ul><ul><li>Often used to make light, heat or work </li></ul>
21. 21. Ohm’s law Watts = volts x amps
22. 22. Practice problems <ul><li>A 1.5 volt AA battery is running a light, the light uses 1.1 amps, what is the resistance of the light? </li></ul><ul><li>My headlights have 1.8 ohms of resistance and use 6.66 amps. What kind of battery should I put in my truck? </li></ul>
23. 23. <ul><li>How many amps does a 100 watt light bulb run? </li></ul><ul><li>What is the resistance of this light bulb? </li></ul><ul><li>What is the resistance of a 300 watt hair dryer? </li></ul>
24. 24. Patterns of circuits <ul><li>Series: </li></ul><ul><li>Circuit where there is only one path for electrons to take </li></ul><ul><li>Light bulbs, what happens to resistance? What happens to the voltage? </li></ul><ul><li>A 9 volt battery has 3 lights on it, what is the voltage drop for each light? </li></ul><ul><li>Batteries, what happens to voltage? </li></ul><ul><li>R total = R 1 +R 2 +R 3 … </li></ul>
25. 25. <ul><li>Parallel </li></ul><ul><li>Branching the path that electrons can take </li></ul><ul><li>Light bulbs, what happens to resistance </li></ul><ul><li>Batteries, what happens to voltage </li></ul><ul><li>1/R total = 1/R 1 +1/R 2 +1/R 3 … </li></ul>
26. 26. <ul><li>I have three 9 volt batteries wired in series, what is my total voltage? If I have two light bulbs wired in series in this circuit what is the voltage drop at each light bulb? </li></ul><ul><li>I have three 9 volt batteries wired in parallel, what is my total voltage? </li></ul><ul><li>I have three light bulbs wired in series that have 10 ohms of resistance each, what is my total resistance? </li></ul>
27. 27. Marathon problem <ul><li>The lights in my garage are wired in parallel. I have three 60 watt incandescent light bulbs and one 20 watt fluorescent light bulb. What is the total resistance of my circuit? </li></ul>
28. 28. Transforming electricity <ul><li>Transformers: </li></ul><ul><li>change the amount of volts and amps in electricity. </li></ul><ul><li>The power company puts out power at 200,000 volts and little amps </li></ul><ul><li>Your house transforms it into 120 volts and 15-20 amps </li></ul>High voltage transformer short
29. 29. <ul><li>Appliances also change the voltage higher or lower </li></ul>
30. 30. How transformers work <ul><li>If primary coil has less coils then voltage is increased </li></ul><ul><li>If the primary coil has more coils the voltage will drop. </li></ul><ul><li>Equation: </li></ul><ul><li>E p /E s = T p /T s </li></ul><ul><li>E= voltage </li></ul><ul><li>T= turns (coils) </li></ul><ul><li>P= primary </li></ul><ul><li>S= secondary </li></ul>
31. 31. <ul><li>Questions </li></ul><ul><li>My alarm clock has 400 coils on the primary side and 100 coils on the secondary side, how many volts does it run off of? </li></ul><ul><li>My printer is plugged into a wall socket, it runs on 32 volts, the primary coil has 45 coils on the primary, how many coils are on the secondary? </li></ul>
32. 32. Effects of transforming electricity on current <ul><li>In a circuit the watts must stay the same. </li></ul>
33. 33. Amps and Volts <ul><li>Equation: </li></ul><ul><li>E p /E s = I s /I p </li></ul><ul><li>E= voltage </li></ul><ul><li>I= amps </li></ul><ul><li>P= primary </li></ul><ul><li>S= secondary </li></ul>
34. 34. Amps of a transformer <ul><li>A plasma TV steps up the 120 volts to 1000 volts. The current in the primary (before the transformer) is 2 amps. What is the current at the secondary? </li></ul>
35. 35. Marathon problem <ul><li>A transformer for a vibrating chair has a primary coil of 150 turns and a secondary coil of 350 turns. It draws 4 amps incoming (primary). What is the resistance of the chair? </li></ul>