1. Do Now (1/23/14): Do not touch the materials on your desk until instructed! 1.What is a magnet? 2.What are some properties of magnets? 3.How do you use magnets in your life? 4.Are some magnets stronger than others?

2. Investigate: Work with your group to complete the activity. You have ten minutes!!!

3. Like repels like… Opposites attract!

5. Magnetism Resources: http://coe.kean.edu/~afonarev/Physics/Mag netism/Magnetic%20Fields%20and%20For ces-eL.htmhttp://coe.kean.edu/~afonarev/Physics/Mag netism/Magnetic%20Fields%20and%20For ces-eL.htm

6. Magnets have been known for centuries. Magnets have been known for centuries. The ancient Greeks used a stone substance called “magnetite.” They discovered that the stone always pointed in the same direction. The ancient Greeks used a stone substance called “magnetite.” They discovered that the stone always pointed in the same direction. Later, stones of magnetite called “lodestones” were used in navigation. Later, stones of magnetite called “lodestones” were used in navigation.

7. What is Magnetism? force of attraction or repulsion of a magnet due to the arrangement of its atoms, particularly its electrons.

8. Magnetic effect is strongest at the poles (ends) Each magnet has 2 poles – 1 north, 1 south.

9. Poles of a magnet always come in pairs!

10. If you cut a magnet in half, you get 2 magnets!

11. Magnetic Fields The region where the magnetic forces act is called the “magnetic field”

12.  Atoms themselves have magnetic properties due to the spin of the atom’s electrons.  These areas of atoms are called “domains”  Groups of atoms join so that their magnetic fields are all going in the same direction

13. 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.

14. An unmagnetized substance looks like this…

15. While a magnetized substance looks like this…

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

17. The Earth is a magnet: Magnetic South Pole Magnetic North Pole surrounded by a magnetic field that is strongest near the North and South magnetic poles Geographic North Pole Geographic South Pole

18. Sometimes, the Earth’s magnetic poles flip. This happens every half- million years or so. Magnetic North Pole Magnetic South Pole

19. Use the Earth’s magnetic field to find direction. The needle of a compass always points toward the magnetic south pole. We call this direction “North” (remember, opposites attract)

21. Do Now (1/24/14): (Do not touch the materials on your desk until instructed!) Write down three things you learned yesterday about magnets

22. Magnetic Field

23. 1) Review: a) Natural permanent magnets –Like poles repel, unlike attract –come in pairs (no monopoles) –Interact with earth; define N (or north-seeking) pole as pole attracted to North pole of earth

24. b) Magnetic field direction: - direction of force on N pole B

25. Review What is an electric dipole?

26. Review: (in your notes) Draw the electric field of an electric dipole

27. Hypothesize (2 min): What do you think the magnetic field of a bar magnet would look like? Draw it in your notes. Discuss with your elbow partner

28. Investigation Work with your table to complete the Investigation. You have twenty minutes to complete the activity.

29. Results: Go to the board and draw the field lines that you discovered. If yours looks like another group’s, put a check mark next to it.

30. Field of a magnetic dipole

31. d) Magnetostatics for poles (identical to electrostatics for charges) –2 types: N, S vs +,- –Unlike attract, like repel –Inverse square law –Force along joining line –Magnetic Field:

32. Why study magnetism? –No monopoles (yet) –Poles (dipoles) produced by moving charges –Charges affected by magnetic field The fundamental unit is still charge –magnetic fields can be created by charge –The force on a charge can be due to magnetic field Magnetic fields do not interact with stationary charges!!!!!

33. Magnetic Field Represented by B Units: Tesla Brainstorm: how big do you think Earth’s magnetic field is? 10 -5 T!!!!!

34. Force on a moving charge in a magnetic field

35. (Alternative definition of B) Proportional to component of v perp to B Perpendicular to B Perpendicular to v

36. Force on a moving charge what would result in a force of zero? charge at rest charge traveling parallel to B

37. Force on a moving charge what would result in a maximum force? charge traveling @ 90° to B

38. Example: What is the force on an electron moving at 43 m/s in a magnetic field of 0.5 T?

39. Practice: Work on the Magnetic Force Worksheet

40. Do Now (1/27/14): (On your Do Now sheet from last week) How fast is a proton moving in a magnetic field of 0.8 T if the magnetic force exerted on it is 0.9 N?

41. Finding Directions of B-Fields Consider an arrow OUT OF THE PAGE INTO THE PAGE

42. The Right Hand Rule! Follow along on your paper Three different methods – find the one that works for you!

43. #1 (ON YOUR PAPER) Direction of v: Direction of B: Direction of F: To the right Out of the page DOWN (TOWARDS THE BOTTOM OF THE PAGE)

44. Practice: Complete the Right Hand Rule Worksheet by the end of class. If you finish early, please continue working on your homework (Magnetic Force)

45. Do Now (1/28/14): 1.Draw the following on your paper: a.A magnetic field pointing to the right b.A proton traveling towards the top of the page c.What is the direction of the force exerted on the charge? 2. If the proton travels at 3000 m/s and the magnetic field has a magnitude of 4 T, what is the force exerted on the proton? 3. What is the proton’s acceleration?

46. RHR: Electron vs. Proton What if an electron travels through the field instead of a proton?

47. 2) Magnetic field due to current (direction) Oersted (1820)

48. Right Hand Rule #2:

49. 3) Magnetic force on current Direction from RHR1: B fingers, I thumb, F palm Force per unit length defines B a) Orthogonal case

50. Practice: Use the rest of class to work on your HW (Magnetic Force and/or Force on a Current- Carrying Wire)

51. Do Now (1/29/14): What is the force on a 15 cm wire carrying a 10 A current surrounded by a 0.2 T?

52. Force on a current carrying wire Look on your homework paper.

53. Example: A current in the +x direction and a magnetic field in the –y direction

54. Investigate! Work on ONE of the investigations for full credit. Work on both for extra credit!

55. Do Now (1/30/14): Come in quietly, pass in your Do Now’s and Homework, then wait for further instructions.

56. Units:

57. b) General case Force per unit length

58. 4) Force between parallel wires

59. Attraction or repulsion? Does it depend on reference frame? + + FEFE FEFE FBFB FBFB v v

60. v v + + - - + + - - + + - -

61. Define Ampere as the quantity of current that produces a force per unit length of 2 x 10 -7 N/m for separation of 1 m Then This defines C and gives

62. Permeability of free space Then

63. 5) Field due to long straight wire (magnitude)

64. 6) Force on a moving charge Zero at rest Zero parallel to B Max perpendicular to B

65. (Alternative definition of B) Proportional to component of v perp to B Perpendicular to B Perpendicular to v

66. 7) Motion of a charge in a magnetic field a) Constant force motion is parabolic electric or gravitational field not everywhere perp to velocity not magnetic field

67. Mass spectrometer: Diagram:

68. b) Constant magnitude perpendicular to motion radial field (circular motion) mass on a string magnetic field produces circular motion (initial vel. perp. to B) motion is circular

69. Force due to the field: For circular motion: So, r depends on v, B angular freq. independent of speed, radius

70. Tracks in a bubble chamber electron-positron creation 1, 3 positive 2 negative energy: 3 > 2 > 1 energy decreases by collisions

71. Example: Find speed and radius for proton B = 0.10 T V = 2100 V

72. c) Work done by magnetic field F displacement, x Work by a force F For a magnetic field, Work = 0

73. d) Velocity selector Force due to E (down): Force due to B (up): For zero deflection, F E = F B :

74. e) Mass Spectrometer Ion energy: Radius of motion:

75. Additional Info about Magnets

76. William Gilbert, an English physician, predicted in 1600 that the Earth would be found to have magnetic poles.

77. The sun has a magnetic field, too. It extends far above the sun’s surface. Other planets in the solar system also have these magnetic fields

78. When a charged particle enters a magnetic field, an electric force is exerted on it. If a charged particle moves at an angle to a magnetic field, the magnetic force acting on it will cause it to move in a spiral around the magnetic field lines.

79. The solar wind is constantly bombarding the Earth’s magnetic field. Sometimes these charged particles penetrate that field. These particles are found in two large regions known as the Van Allen Belts.

80. The Earth’s magnetic field extends far into space. It is called the “magnetosphere.” When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called…

81. The Aurora Borealis in the Northern Hemisphere And the Aurora Australis in the Southern Hemisphere