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# Lecture 13 2 26 2004

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### Lecture 13 2 26 2004

1. 1. Magnetism<br />Similar to electric forces<br />Magnetic Poles <br />North and South Poles<br />Historic Designations<br />Like Poles Repel, Unlike Poles Attract<br />Due to alignment of atoms in material<br />
2. 2. Magnetic Fields<br />Similar to electric and gravitational fields<br />Magnetic fields are produced by the MOTION of electric charges<br />
3. 3. Magnetic Fields<br />Revolving electron produces field<br />Spinning electron produces field<br />In most atoms, combination of spins and orbits are in opposite directions<br />The fields cancel each other out<br />Some atoms, they don’t cancel<br />Iron, nickel, cobalt, aluminum<br />
4. 4. Magnetic Domains<br />In iron, for example, field by an atom is so strong it causes neighboring atoms to arrange their spins and orbits to line up<br />These clusters form magnetic domains<br />Domains are randomly oriented in ordinary iron, nickel, etc.<br />Can force them to line up with external field<br />
5. 5. Electric Currents & Magnetism<br />A moving charge produces a magnetic field<br />
6. 6. Electric Currents & Magnetism<br />
7. 7. Electromagnetics<br />Place a piece of unmagnetized iron in a coil of wire carrying a current<br />Produce a strong magnetic field in the iron by lining up domains<br />Makes the whole thing a very powerful magnet<br />
8. 8. Magnetic Forces and Charges<br />If a charge isn’t moving, a magnetic field has no effect on the charge<br />Reciprocal kind of idea<br />Moving charges produce magnetic fields<br />Magnetic fields apply a force to a moving charge<br />
9. 9. Magnetic Forces and Charges<br />
10. 10. Magnetic Forces and Charges<br />
11. 11. Magnetic Forces and Charges<br />
12. 12. Meters<br />Use a compass needle (magnet)<br />
13. 13. Meters<br />
14. 14. Motors<br />
15. 15. Electromagnetic Induction<br />
16. 16. Electromagnetic Induction<br />
17. 17. Electromagnetic Induction<br />
18. 18. Electromagnetic Induction<br />
19. 19. Electromagnetic Induction<br />Faraday’s Law<br />The induced voltage in a coil is proportional to the number of loops, multiplied by the rate at which the magnetic field changes within those loops.<br />The amount of current depends on the resistance of the wire<br />Changing magnetic field in a loop is key!!<br />
20. 20. Electromagnetic Induction<br />Traffic light control (buried loops)<br />Airport Security Systems<br />Mag strips on credit cards<br />Tape Recorders<br />Computer Hard Drives<br />
21. 21. Generators<br />
22. 22. Generators<br />
23. 23. Power Production<br />
24. 24. Transformers<br />
25. 25. Transformers<br />The more turns, the more voltage induced<br />Step-up Transformer has more turns in secondary than in primary<br />Step-down Transformer has more turns in primary than in secondar<br />
26. 26. Transformers<br />Energy Conservation<br />Power In = Power Out<br />
27. 27. Field Induction<br />An electric field is induced in any region of space in which a magnetic field is changing with time<br />A magnetic field is induced in any region of space in which an electric field is changing with time<br />“Let there be light!!!”<br />