1. Magnetism

2. Magnet Properties
All magnets have polarity - a North Pole and a South Pole
If you cut magnet in half…….
Can you make a monopole? N S
It makes two magnets! N S N S
No – a chopped magnet will turn itself into two N/S magnets

3. Magnetism and Planet Earth
Like poles repel, Opposites attract (N and S)
North Pole of suspended magnet (compass) seeks geographic South
So why do compasses point north?
Because the magnetic pole in the N. Hemisphere is in actuality the SOUTH MAGNETIC pole of the Earths magnetic field!!!
Geographic North & Magnetic South
Geographic South & Magnetic North

4. Magnetism and Planet Earth
Remember: The north geographic pole is near the south magnetic pole of the earth (and vice versa)

5. Magnet Make-up Only certain materials can be magnetized Iron (Fe)
Gadolinium (Gd)
Cobalt (Co)
Nickel (Ni)
These materials are ferromagnetic

6. Where does magnetism come from?
Oersted discovered that moving electric charges create magnetic fields
All magnetism arises from MOVING ELECTRIC CHARGES
Spin of electrons in atom creates a magnetic domain
If magnetic domains
are aligned, then
material is magnetic

7. How to Ruin a Magnet
To ruin a magnet, cause the magnetic domains to become randomized
Drop it
Heat it
The Curie temperature is the temperature above which a material loses all magnetic properties
Expose it to another magnetic field
VHS and cassette tapes record sound/video by aligning magnetic material on the tape.

8. How to Create a (Temporary) Magnet
Place an object made of a ferromagnetic substance in a larger magnetic field
Rub the object over and over again in the same direction (aligns magnetic domains)
Run current through a coil of wire (electromagnet)

9. Drawing Magnetic Field Lines
Magnetic Field lines are drawn as loops
Point from NORTH to SOUTH
How to draw magnetic field lines for the Earth?
Point up from southern hemisphere (magnetic North) toward northern hemisphere (magnetic south)
If the dark part of my compass is “north,” which way should it point when put to the right of the magnet?
I I I I I I I I I I I I
I I I I I I I I I I I I

10. Electromagnets A solenoid is a current-running coil of wire
Produces a magnetic field like the magnetic field of a bar magnet.
Found in doorbells, car starters
Electromagnet – A solenoid that is wrapped around a ferromagnetic core
To make an electromagnet, all you need is:
Wire (the more loops the better)
Battery (the more voltage the better)
Ferromagnetic core

11. From here on out we will refer to a magnetic field as a B-field
Magnetic Force
From here on out we will refer to a
magnetic field as a B-field
A charge will feel the greatest force when it is moving PERPENDICULAR to the B-Field
Charge feels no net force if it is moving PARALLEL to the B-Field

12. Magnetic Fields Symbols for drawing B-fields:
Arrows – going left/right or up/down
into the page (like seeing an arrow on a target)
out of the page (like seeing an arrow coming toward you)
Point charges move PARALLEL to electric fields and PERPENDICULAR to magnetic fields

13. B-Field Around a Wire Right-hand rule
Thumb = direction of current flow
Wrap fingers as if grabbing wire
Fingers show you direction of B-Field
into the page
out of the page

14. Magnetic Force – Point Charge
Magnetic fields are described using Tesla (T).
A particle carrying a charge of 1 coulomb and passing through a magnetic field of 1 tesla at a speed of 1 meter per second perpendicular to said field experiences a force with magnitude 1 newton
Two magnets will apply a Force on each other
Therefore, moving electric charge (which has a B-field around it) can be forced to move by another B-field
Fm = Force (Newtons)
q = Charge (Coulombs)
v = velocity (m/s)
B = Magnetic Field (Tesla)

15. Magnetic Force on Current-Carrying Wire
F: Force in Newtons
I: current in Amps
L: length in meters (direction of current)
B: magnetic field in Tesla

16. B-Field around a Wire in a Loop
More loops = stronger B-Field
Direction of the B-field depends on current flow through the wire
A coil of wire is called a solenoid
You can magnetize a solenoid by running electrical current through it I

17. Right-Hand Rule
This technique helps you to figure out which way the magnetic force is directed.
Thumb: force (F)
Forefinger: velocity or current (v or I)
Middle finger: magnetic field (B)
Negative Q: F is same as the thumb’s direction
Negative Q: F is opposite the thumb’s direction
Force x
v or I
field

18. Physics Gang Symbols
To determine the direction of the variables in our two equations, we need to know the “Physics gang symbols”
These directions are for ELECTRONS
Thumb = direction of B-field (thumb tip points like arrow)
Remember – “ThumB” has a “B” in it
First finger = direction of the velocity
Remember - ONE finger – ONE object has ONE velocity
All other fingers = force
FingerS – NewtonS (both end in ‘s’)
Fingertips point toward force felt by electron
Knuckles point toward force felt by proton

19. Physics Gang Symbols
Determine the direction of the velocity of the electron for each scenario. - B F - B F - B
is out of the page
V =
(out of the page) F
V =
(into the page)
V = - B
is into the page F
V =

20. Sample Problem #1
An electron in a beam experiences a downward force of 2 E -14 N while traveling in a magnetic field of 8.3 E -3 Tesla directed to the West. Find the DIRECTION and MAGNITUDE of the velocity of the electron. - B F

21. Sample Problem #2
A PROTON traveling in a magnetic field experiences a downward force of 2 x N of 8.3 x 10-3 Tesla directed to the West. Find the DIRECTION and MAGNITUDE of the proton’s velocity. + B F

22. Electricity
Magnetism
+ and – charges
N and S poles
like charges repel
like poles repel
unlike charges attract
unlike poles attract
electric monopole exists
no magnetic monopole
electric field lines flow
from + to -
magnetic field lines flow
from N to S
density of lines equals
strength of E
strength of B
SI unit: ampere,
1 A = 1 C/sec
SI unit: Tesla,
1 T = 1 N/Amp meter
E exerts force on a charge,
or E = F/q
Field exerts force on a moving
charge, or B = F/(qvsin)