1. Forces: F net causes acceleration. Forces – act at distance F g – attractive btw masses. F e – attractive/repulsive between objects w net charge. F mag magnetic- attractive/repulsive between objects w net e- spin.. Field g = F g /m. Test mass. E = F e /q. + Test charge. B ~ currents in wire. Compass needle.

2. Magnetism

3. What is Magnetism? Magnetism is the force of attraction or repulsion of a material due to the spin of its electrons. Like all forces F mag can be a F net that causes acceleration & is measured in N.

4. Magnetic Fields regions of space around a magnet where magnetic materials feel a force.

5. Magnets create a force field which will deflect a compass needle. Field lines point in the direction of the deflection of the compass needle. Through Magnet.

6. The poles of a magnet are where the magnetic effect is the strongest. Each magnet has 2 poles –north, south. Field lines are close where field is strong.

7. Field lines come out of N pole, go into S pole. Lines never touch or cross Only curves Field lines called lines of flux. Flux density shows field strength.

8. Ex: Make a rough sketch of the horseshoe magnet below. Sketch the field lines near the ends of the magnet.

9. More than 1 magnet – out of N, into S.

10. Earth has a mag. field. The north seeking end of a compass points toward Earth’s N geographic pole.

11. Earth’s north pole acts like south pole of bar magnet.

12. Demo Magnetic Field Lines magnet on iron bars.

13. What causes magnetism?

14.  Atoms have magnetic fields due to excess e- spin.  These areas of atoms are called “domains”  Groups of atoms join so that their magnetic fields are all going in the same direction.

15. When an unmagnetized substance is placed in a magnetic field, the substance can become magnetized. This happens when the spinning electrons line up in the same direction.

16. An unmagnetized substance looks like this…

17. While a magnetized substance looks like this…

18. Poles of a magnet always come in pairs!

19. How to break a magnet: 1. Drop it 2. Heat it This causes the domains to become random again!

20. Non-magnets with magnetic properties can be polarized in the presence of a magnetic field. N N S S

21. Minute Physics How do magnets work 6.5 minutes. http://www.youtube.com/watch?v=hFAOX dXZ5TMhttp://www.youtube.com/watch?v=hFAOX dXZ5TM

22. Hwk Intro Sheet.

23. Relationship of Electricity & Magnetism

24. Similarities of Magnetic (B) to Electric Fields (E) field lines also called lines of flux. Both attract opposite. Repel like. Drop off with d 2. Both Polarize objects. Flux density shows intensity of field. Both vector quantities.

25. Differences For B field, direction compass needle points. E field direction + test charge would move Magnet feels no force in static E field. Charges feel no force in static B field. Isolated poles do not exist. Isolated charges do.

26. Electromagnetism 57 Min. http://www.youtube.com/watch?v=bht9AJ1 eNYchttp://www.youtube.com/watch?v=bht9AJ1 eNYc Old Navy film How magnetism produce Electricity 7 min. http://www.youtube.com/watch?v=uoQelu7 XRjkhttp://www.youtube.com/watch?v=uoQelu7 XRjk

28. -Moving charges cause magnetic fields. When a current flows, a magnetic field is generated. *Stationary charges do not cause magnetic fields, but do cause electric fields.

29. Sketching Fields Use arrows to show the direction of compass needle deflection.

30. Field into the page X like tail of arrow. Field out of page … like tip of arrow.

33. Mag Field Direction around Wire.

35. 2 nd Hand Rule: Wire loop – thumb in current direction. Fingers in B direction.

36. Solenoid – Coils of wire (can be wrapped around core of iron).

37. 3 rd hand rule: Fingers in direction of current. Thumb points to magnetic N. Pole. Solenoids act like bar magnets.

38. Charged particles moving in B fields feel a force!! Force direction determined by hand rule three.

39. Fourth

40. Direction of mag force on q perpendicular to v vector & to B field. For +q place right hand fingers into field, thumb points to v, palm points to mag force. For – q use left hand.

41. Electron in mag field B.

42. Force is proportional to amount of charge on particle.

43. Force on current carrying wire. The current in a wire also feels a force in mag field.

44. Fifth hand rule:–force direction on wire: fingers into field, thumb in current direction, palm points toward force direction.

45. Currents in same direction exert attractive forces.

46. Current in opposite directions, create fields with repulsive forces. I 1 I 2 F1F1 F2F2 By Newton’s 3 rd Law, F 2 = -F 1.

47. The Ampere (A) is a unit of rate of current flow, but is based on the force felt between 2 current- carrying wires. The Ampere, not the Coulomb, is considered a fundamental unit!! Very weird indeed!

48. For a straight length of wire the induced B field drops off with distance (r). The circles should get… B =  o I  o constant find it. 2  r r = dist fr wire m I = current - A B = field strength T

49. Mag Field Strength around a solenoid: B =  o NI N = number turns of wire lI = current l = length of wire in field m

50. Force between two wires proportional to current in wires: F =  o I 1 I 2 l 2  r

51. Ex 4: What is the magnitude & direction of the force btw 5.00 m lengths of wire each carrying 7.5 A of current in the same direction if they are separated by 25.0 cm? 2.25 x 10 -4 N toward each other.

52. Mag Field Between Current Carrying Wires. These show neg charge flow.