1. Electromagnetism

2. Magnets Made from alloys of iron, nickel and cobalt
Each Magnet has two poles!
Magnetic poles are areas of concentrated magnetic force
When left to rotate freely,
One pole will seek (point to) the northerly direction on Earth – referred to as North Pole
One pole will seek the southerly direction on Earth – referred to as South Pole

3. Laws of Magnetic Poles
Opposite magnetic poles attract
Similar magnetic poles repel
Forces of attraction and repulsion are felt “at a distance” – affect each other before they touch (like gravity)

4. Magnetic Field of Force – the space around a magnet in which magnetic forces are exerted

6. Characteristics of Magnetic Field Lines
1) The spacing of the lines indicates the relative strength of the force
The closer the lines are the greater the force
2) Outside a magnet, lines are concentrated at the poles.
They are closer inside the magnet itself

9. Characteristics of Magnetic Field Lines
By convention, the lines proceed from S to N inside a magnet and from N to S outside a magnet
All lines form closed loops
Lines do not cross each other

11. Domain theory of Magnets
Atoms in ferromagnetic materials can be thought of as tiny magnets with N and S poles – these tiny atomic magnets are called dipoles
Each dipole can affect its neighbor, causing their dipoles to line up in the same direction – when this happens, called an electric domain

12. Nickel, cobalt and any alloy containing iron, nickel or cobalt can become magnetized by bringing them close to a magnet – these materials are called FERROMAGNETIC

14. Unmagnetized Domain
dipoles lined up in each domain (group) but each domain is pointing randomly in different directions
When an unmagnetized piece of iron is placed in a magnetic field (near another magnet) – the dipoles act like small compasses and rotate until they are all aligned with the magnetic field

15. Magnetized Domain
Dipoles all line up in the same direction causing one end to become the north pole and one end to become the south pole

16. Effects of the Domain Theory
1) Magnetic Induction
A permanent magnet brought close to a piece of unmagnetized iron can force the poles of individual domains to align, turning it into a magnet
Magnetic Induction – process of magnetizing an object from a distance

17. Effects of the Domain Theory
Magnetic Induction
Soft Iron: iron that loses its magnetism as the magnet moves away
Hard Iron: iron that retains its magnetism as the magnet moves away

18. Effects of the Domain Theory
2) Demagnetization
Dropping or heating a magnet will demagnetize it – dipoles will go back into a random alignment

19. Effects of the Domain Theory
3) Reverse Magnetization
If a bar magnet is placed in a strong enough magnetic field of opposite polarity, its domains can switch – the N- pole becomes S-pole, etc

20. Effects of the Domain Theory
4) Breaking a Bar Magnet
Breaking a bar magnet creates 2 magnets with the same poles/alignment of dipoles

21. Effects of the Domain Theory
5) Magnetic Saturation
Occurs when the maximum number of poles are aligned, this determines the maximum strength of the magnet

22. Effects of the Domain Theory
6) Induced Magnetism by Earth
If a piece of iron is held in Earth’s magnetic field pointing north and its atoms are agitated by heating or mechanical vibrations, its dipoles can align, creating a magnet
Steel columns in buildings, ships and railway tracks are often magnetized

23. Principle of Electromagnetism: Moving electric charges produce a magnetic field.

24. Right-Hand Rule for a Straight Conductor: If a conductor is grasped in the right hand, with the thumb pointing in the direction of the current and the curled fingers point in the direction of the magnetic field lines

25. RHR straight conductor
SUMMARY
Fingers  B (magnetic field)
Thumb  I (current)

26. 8.1 Electromagnetism

27. Solenoid: a coil of wire

28. Right-Hand Rule for a Solenoid: If a solenoid is grasped in the right hand, with curled fingers point in the direction of the electric current and the thumb pointing in the direction of the magnetic field lines in its core.

29. RHR Solenoid SUMMARY
Thumb  B (magnetic field)
Fingers  I (current)

30. 8.1 Electromagnetism

31. Note: The RHR is for conventional current flow; meaning the charge is positive.

32. The Geographic North pole is the Earth's magnetic south pole
The Geographic North pole is the Earth's magnetic south pole. The magnetic poles have switched back and forth through out Earth's history.

33. 8.1 Practice Questions
Page 391 Questions 1-5

34. 8.2 Magnetic Force on Moving Charges

35. The size of a magnetic force on a charged particle is: 1
The size of a magnetic force on a charged particle is: 1. directly proportional to the size of the magnetic field, velocity, and the charge of the particle.

36. 2. is dependent on the angle,  between the direction of the magnetic field and the direction of the velocity. The force is proportional to sin.

37. Fm = qvBsin
where Fm = magnitude of the magnetic force (in N) q = magnitude of charge (in C) v = speed (in m/s) B = magnitude of the magnet field (in T)  = angle between the direction of magnetic field and velocity

38. 8.2 Magnetic Force on Moving Charges
Thus,
B = __Fm__
qvsin

39. 8.2 Magnetic Force on Moving Charges
Note: The SI unit of magnetic field strength is Tesla. 1T = 1 Tesla 1 T = 1 kg/(C•s)

40. 8.2 Magnetic Force on Moving Charges
Motor Principle (Right Hand Rule):
Thumb – direction of current, I
Index finger (pointer finger) – direction of magnetic field
Middle finger – direction of magnetic force [or use out from palm]

41. 8.2 Magnetic Force on Moving Charges

42. 8.2 Magnetic Force on Moving Charges
Example #1: An electron moves into a magnetic field of 0.50T [forwards] at a velocity of 5.0Mm/s[leftwards]. Calculate the magnetic force.

43. CATHODE TUBES

44. 8.2 Magnetic Force on Moving Charges
Read Paragraph on Cathode tube on page 396.

46. 8.2 Magnetic Force on Moving Charges
Thompson’s research lead to the development of the mass spectrometer, used cathode tube to deflect electrons. The electrons get deflected along a circular arc of radius, r.

47. 8.2 Magnetic Force on Moving Charges
Derive 𝒒 𝒎 = 𝜺 𝑩 𝟐 𝒓 starting at net force.

48. 8.2 Magnetic Force on Moving Charges
Note for q=e, q_ = _ε_ m B2r

49. 8.2 Magnetic Force on Moving Charges
Note: e/m = 1.76 X 1011 C/kg

50. 8.2 Magnetic Force on Moving Charges
Example #2: Find the mass of an electron knowing e = 1.6 X C and e/m = 1.76 X 1011 C/kg.

51. spectrometer, through an electric field with a magnitude of 2.23 X
Example #3: Calculate the mass of fluorine-ion (charge of -1e) that has a charge of X C and is accelerated into a mass
spectrometer, through an electric
field with a magnitude of 2.23 X
105N/C into a 2.00T field. The radius of the curved path is 1.1 cm. (Solution on Blackboard)

52. Copy the following in your notes

53. 8.2 Practice Questions
Page 376 Q1-5
Page 402 Q1,2,7