1. White board your results. In particular:
Field Around Magnet
Use a compass to map the direction of the magnetic field surrounding a magnet.
White board your results. In particular:
how does the strength of the field vary with distance from the wire?
how does the field direction relate to the poles of the magnet?
General Physics 2
Magnetism

2. Activity: Map Field of Magnets
Use iron filings to map the field of a
bar magnet
horseshoe magnet
White board results
draw field lines.
how might magnets generate magnetic fields?
General Physics 2
Magnetism

3. direction of magnetic field, B, is parallel to field line
Magnetic Field Lines
direction of magnetic field, B, is parallel to field line
number of lines per area is proportional to strength of field
field lines point
from N to S
field lines form closed loops
General Physics 2
Magnetism

4. Magnetism
No magnetic monopoles!
General Physics 2
Magnetism

5. Magnets are similar to Electric Dipoles
General Physics 2
Magnetism

6. Ferromagnetism Ferromagnetic material Preferentially Random downwards
iron or other materials that can be made into magnets
You can make a magnet from iron by placing it in a strong B field
individual domains become aligned with external B field
Loss of magnetism from:
dropping
heating
Curie temperature
1043 K for iron
Preferentially
downwards
Random
General Physics 2
Magnetism

7. Cross Product – Right Hand Rule
General Physics 2
Magnetism

8. Specifying 3 Dimensions
out of page
tip of arrow
into page
tail of arrow
General Physics 2
Magnetism

9. Force on a moving charge
Right Hand Rule (#2)
qv = fingers
B = bend fingers
F = thumb
Find the direction of the force on a negative charge for each diagram shown.
General Physics 2
Magnetism

10. General Physics 2
Magnetism

11. Think-Pair-Share
Derive an expression for the radius of an e-’s orbit in a uniform B field. Express your answer in terms of me, v, qe, and B. Turn in your solution!
Start of class 2 - students have already completed worksheets 1 & 2
General Physics 2
Magnetism

12. Earth’s Magnetic Field
magnetic declination
angular difference between geographic north and magnetic north
varies with latitude
General Physics 2
Magnetism

15. Tactics: Right-hand rule for fields

16. The Source of the Magnetic Field: Moving Charges
The magnetic field of a charged particle q moving with velocity v is given by the Biot-Savart law:
where r is the distance from the charge and θ is the angle between v and r.
The Biot-Savart law can be written in terms of the cross product as

17. EXAMPLE 33.1 The magnetic field of a proton
QUESTION:

18. EXAMPLE 33.1 The magnetic field of a proton

19. EXAMPLE 33.1 The magnetic field of a proton

20. EXAMPLE 33.1 The magnetic field of a proton

21. The Magnetic Field of a Current
The magnetic field of a long, straight wire carrying current I, at a distance d from the wire is
The magnetic field at the center of a coil of N turns and radius R, carrying a current I is

22. EXAMPLE 33.4 The magnetic field strength near a heater wire
QUESTION:

23. EXAMPLE 33.4 The magnetic field strength near a heater wire

24. Magnetism: Worksheets 1 and 2 Finish before next class
Practice Problems
Magnetism: Worksheets 1 and 2
Finish before next class
General Physics 2
Magnetism

26. Tactics: Finding the magnetic field direction of a current loop

27. Magnetic Dipoles
The magnetic dipole moment of a current loop enclosing an area A is defined as
The SI units of the magnetic dipole moment are A m2. The on-axis field of a magnetic dipole is

28. EXAMPLE 33.7 The field of a magnetic dipole
QUESTIONS:

29. EXAMPLE 33.7 The field of a magnetic dipole

30. Tactics: Evaluating line integrals

31. Ampère’s law
Whenever total current Ithrough passes through an area bounded by a closed curve, the line integral of the magnetic field around the curve is given by Ampère’s law:

32. The strength of the uniform magnetic field inside a solenoid is
where n = N/l is the number of turns per unit length.

33. The Magnetic Force on a Moving Charge
The magnetic force on a charge q as it moves through a magnetic field B with velocity v is
where α is the angle between v and B.

35. Magnetic Forces on Current-Carrying Wires
Consider a segment of wire of length l carrying current I in the direction of the vector l. The wire exists in a constant magnetic field B. The magnetic force on the wire is
where α is the angle between the direction of the current and the magnetic field.

36. EXAMPLE 33.13 Magnetic Levitation
QUESTION:

37. EXAMPLE 33.13 Magnetic Levitation

39. General Principles

40. General Principles

41. General Principles

42. Applications

43. Applications

44. Applications

45. Does the compass needle rotate clockwise (cw), counterclockwise (ccw) or not at all?
STT32.1
Answer: C

46. Does the compass needle rotate clockwise (cw), counterclockwise (ccw) or not at all?
STT32.1

47. The magnetic field at the position P points
Into the page.
Up.
Down.
Out of the page.
STT32.2
Answer: D

48. The magnetic field at the position P points
Into the page.
Up.
Down.
Out of the page.
STT32.2

49. The positive charge is moving straight out of the page
The positive charge is moving straight out of the page. What is the direction of the magnetic field at the position of the dot?
Left
Right
Down Up
STT32.3
Answer: C

50. The positive charge is moving straight out of the page
The positive charge is moving straight out of the page. What is the direction of the magnetic field at the position of the dot?
Left
Right
Down Up
STT32.3

51. What is the current direction in this loop
What is the current direction in this loop? And which side of the loop is the north pole?
Current counterclockwise, north pole on bottom
Current clockwise; north pole on bottom
Current counterclockwise, north pole on top
Current clockwise; north pole on top
STT32.4
Answer: B

52. What is the current direction in this loop
What is the current direction in this loop? And which side of the loop is the north pole?
Current counterclockwise, north pole on bottom
Current clockwise; north pole on bottom
Current counterclockwise, north pole on top
Current clockwise; north pole on top
STT32.4

53. An electron moves perpendicular to a magnetic field
An electron moves perpendicular to a magnetic field. What is the direction of ?
Left
Into the page
Out of the page Up
Down
STT32.5
Answer: B

54. An electron moves perpendicular to a magnetic field
An electron moves perpendicular to a magnetic field. What is the direction of ?
Left
Into the page
Out of the page Up
Down
STT32.5

55. What is the current direction in the loop?
STT32.6
Answer: B
Out of the page at the top of the loop, into the page at the bottom.
Out of the page at the bottom of the loop, into the page at the top.

56. What is the current direction in the loop?
STT32.6
Out of the page at the top of the loop, into the page at the bottom.
Out of the page at the bottom of the loop, into the page at the top.

57. Which magnet or magnets produced this induced magnetic dipole?
a or d
a or c
b or d
b or c
any of a, b, c or d
STT32.7
Answer: B

58. Which magnet or magnets produced this induced magnetic dipole?
a or d
a or c
b or d
b or c
any of a, b, c or d
STT32.7