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Magnet: what is it?

Magnet: what is it?. Rock from Asia. Magnet: what’s it do?. “North”. Magnet: what’s it do?. S. N. North. A compass. S. N. Definition: the North end (pole) of a magnet is the end which wants to point towards the geographic North pole of Earth!. Trouble:. Trouble:.

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Magnet: what is it?

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  1. Magnet: what is it? Rock from Asia.

  2. Magnet: what’s it do? “North”

  3. Magnet: what’s it do? S N North

  4. A compass S N

  5. Definition: the North end (pole) of a magnet is the end which wants to point towards the geographic North pole of Earth!

  6. Trouble:

  7. Trouble:

  8. Compasses (magnets) interact! The north pole of a magnet seems attracted to the south pole of another, and vice-versa! Scientific: make a little compass, and test it out around a big one! Compass sim (Remember not to close it !!!) http://phet.colorado.edu/en/simulation/magnet-and-compass

  9. Field lines around a (bar) magnet S N

  10. Semi-Definition of a magnetic field (produced by some magnet) Pick a point in space. Put a small test compass there. points in the direction of the compass…. (the way the north end points). Strength seems to have something to do with distance (magnitude B comes later) Back to sim!! (don’t close it) Compass sim Show field

  11. Maybe Earth is a big Magnet? But it must be that the North geographic pole is a South magnetic pole: Back to sim!! (don’t close it) Compass sim

  12. Astounding fact: electric currents affect compasses! Wire with no current ( I = 0).

  13. Astounding fact: electric currents affect compasses! current on ( Iup !).

  14. Astounding fact: electric currents affect compasses! current on ( Idown !).

  15. current on ( Iup !).

  16. current on ( Iup !).

  17. Right hand rule (#1)

  18. ( Iup/out !). DIRECTION?

  19. ( Idown/in !). DIRECTION?

  20. ( I= 0 ). DIRECTION?

  21. Current Loop: down/in up/out

  22. Back to sim!! (don’t close it) Compass sim

  23. Remember how it was with electric fields: action at a distance:

  24. Remember how it was with electric fields: Field concept: Charge Q1 SOURCE

  25. Remember how it was with electric fields: Field concept: Charge Q2 SOURCE

  26. Same idea for B-fields: Current S N Magnet

  27. Same idea for B-fields: Forces on Magnet Current S N SOURCE

  28. Same idea for B-fields: Force on Current ? Magnet S N SOURCE DEMO to prove it! Hanging wire

  29. To define the magnitude of B we have to do some kind of experiment Why not put a wire with a known current into a uniform B-field? How do we make a uniform B-field?

  30. How do we make a uniform B-field? N S N S Each magnet produces an individual magnetic-field, so ….

  31. How do we make a uniform B-field? N S N S …the total field due to both is just the (vector) sum of each individual field

  32. How do we make a uniform B-field? N S N S Bring them close S N

  33. Now the experiment!! S N Wire with no current ( I = 0).

  34. Now the experiment!! S N Wire with current ( I = out/up).

  35. Now the experiment!! S N Wire with current ( I = in/down).

  36. RESULTS I: Force on the wire is always perpendicular to bothB and the direction of I – in a right-handed kind of way Conventional current!

  37. Right-Hand rule (#2) “I crossed into B gives F” DEMO examples with current swing

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