1. MAGNETISM Adapted from Mr. Dellibovi
print handouts at 6 to a page for a 4 page student guide

2. Magnets- History and Interesting Facts
Lodestones
Natural Magnets
Magnetite, Fe3O4 (an oxide of iron)
Ancient civilizations (Greek 590 BCE, Chinese 2600 BCE) realized that these stones would cling to iron tools.
A suspended, pivoting lodestone always pointed along the North-South axis
Magnetite crystals have been found in living organisms
Magnetotactic bacteria!
Migratory Bird brains!!
Other migratory animals: bees, fish
Human brains!!!
YOU HAVE ROCKS IN YOUR HEAD!!!!!

3. History of Permanent Magnets
By 2nd Century AD, Chinese were able to make permanent magnets by repeatedly __________________________________________________________________________________________________________________.
Retained strength of a magnet depends on ___________________________________.
________: loses magnetism quickly
_________________ (paper clips, nails): gradual loss
________: retains power for a long time and is referred to as a “permanent magnet”

4. Magnetic Poles Magnets produce a force on other objects
Poles are regions where the magnetic force is the strongest
Like magnetic poles _______________.
Opposite magnetic poles _____________.
Most magnets have ______ poles (dipole), but can have three or more!

5. Monopole? (No, not Monopoly!)
Monopole: piece of a magnet that is simply a north pole or a south pole
Many have tried to isolate a monopole by breaking magnets in half.
No matter how we break a magnet, the pieces are always dipoles!
________________________________________
Do not pass GO. Do not collect $200.

6. Magnetic Field
Every magnet establishes in the space surrounding it, a magnetic field (B-field)
Map field with a _____________________
Direction of field is direction in which the test-compass needle will point at that location.
Draw field lines so that compass always points _______ to the field lines.
Field lines point from N to S __________ the magnet
Field lines point from S to N __________ the magnet
Field lines form closed loops
Field lines never _____________________
SI unit for B (magnetic field strength) is the tesla (T)

7. Magnetic Field Mapping with Test-Compass Field Lines Form Closed Loops
Field Mapped by Iron Filings

8. Earth’s Magnetism
Magnetic field has reversed direction ~300 times in the past 170 million years
Magnetic poles wander!
Magnetic & geographic poles not the same.
Magnetic declination: 11.5°
What’s strange about this picture? ____________________________________________________________

9. Diagramming 3-D Magnetic Fields
Not everybody is an artist.
Use 2-D images to draw 3-D field vectors.
If field points perpendicularly into the page or board, use
If field points perpendicularly out of the page or board, use
Otherwise, draw the lines neatly.
Don’t forget, field lines are vectors!

10. Magnetism on an Atomic Level
Charge ________________ (or electric __________) produces magnetic force
Electrons function as a subatomic dipole
Electron “spin”
Electrons existing in pairs: B-fields cancel
Electron “orbit” around nucleus
Random “orbits” of electrons: B-fields cancel

11. Diamagnetism
Even “non magnetic” materials respond to an applied B-field
Applied B-field changes orbital motion of electrons
Produces a field that _____________ applied field
______________ by applied field
Diamagnetic materials have no _____________ atomic dipoles
Occurs for ______ substances, but may be swamped by other magnetic effects

12. Paramagnetism
Paramagnetic materials are ___________ when placed in a strong B-field.
Composed of atoms with ____________ atomic dipoles
Atomic dipoles do not interact w/ one another
Atomic dipoles oriented randomly
Material has no dipole as a whole
A strong B-field re-orients these atomic dipoles in _____________ as applied field

13. Ferromagnetism
Naturally “magnetic”: magnetite, iron, nickel, cobalt, steel, Alnico, other alloys
Strongly attracted to poles of a magnet
Easily magnetized
Atomic dipoles ____________ with dipoles of adjacent atoms
Dipoles align spontaneously, w/o an applied field
Many atomic dipoles cooperatively align
Creates regions of __________ orientations (_____________)

14. Magnetic Domains Domain: region where many atomic dipoles _________
Usually aligned randomly and effects cancel
BUT…
Place ferromagnetic material in strong B-field
Entire domains realign with applied field
Size & shape of domains remains the same
Causes irreversible re-orientation of domains
Creates permanent magnets

15. Reorientation of Domains
Electrons in domains align with applied field
Substance is Permanently Magnetized
Domains are not aligned

16. Electrodynamics: The Study of Electromagnetism
Magnetism is caused by charge in motion.
Charges at rest have just an electric field
But, when they move, they generate both an electric field and a magnetic field
Can look at individual charges or electric current in a wire
Direction of current determines direction of the magnetic field.
Use right hand rules for analysis.

17. First Right Hand Rule: thumb points in direction of _________, fingers curl in direction of ____________ . Note compass readings. Use for: ___________________

18. Magnetic field of a long straight wire
B: magnetic field strength (teslas)
I: current (amperes)
r: radius from wire
μo: ____________________________________
μo =
The shape of this magnetic field is: _________________ _____________________________________________

19. 1st Right Hand Rule- Thumb points in the direction of the current, fingers curl in the direction of the created magnetic field – up through the coils and around the outside. Use for ________________________________________________
Fig 19.20b, p.682
Slide 19

20. Magnetic field of loops of wire (or a coil) carrying current
where n is the NUMBER of loops (in this example n=8)
How is this equation different from the mag field of a straight wire?
The strength of the field is more in a loop than in the straight wire and a single loop.

21. 2ND Right Hand Rule
Gives the direction of the FORCE exerted on a current (or charge) by an external magnetic field
Point thumb of RH in direction of current (or motion of positive charge)
Point fingers through in direction of magnetic field
Palm pushes in direction of ___________

22. 2ND Right Hand Rule
Fingers point to B, the direction of magnetic field lines.
Thumb points to v, which is direction of velocity of positive charge
Deflecting force is shown by direction of palm pushing.

23. 2ND Right Hand Rule

24. Magnetic Force on a Moving Charge
F = Bqv·sin Θ
B: field strength in _____________
q: charge in _________________
v: charge velocity in ____________
Θ: angle between __________

25. Magnetic Force on a Current-Carrying Wire
F = B·I·L
B: field strength in _______________
I: current in ______________
L: length of current-carrying wire in __________