Magnetism has been observed for over 2000 years, with lodestones found in ancient Greece exhibiting magnetic properties. In the 1820s, Hans Christian Oersted discovered the relationship between electricity and magnetism when an electric current caused a compass needle to deflect. Magnets have both north and south poles and magnetic fields that exert forces on other magnetic and electrically charged objects. The strength of this magnetic force depends on factors like the distance from the magnet, the velocity and charge of the object, and the magnetic field strength.

1. Magnetism
2000 years ago, rocks in Magnesia, Greece were found
to have weird properties. Later called “lodestones.”
Hans Christian Oersted
(Danish Science Professor, 1820)
 Discovered relationship
between electricity and
magnetism accidentally while
demonstrating electric currents.
These caused a compass needle
to tip.

2. Similarities to Electricity
• Exert non-contact force
– Has a Field
• Strength of force depends on distance
• Attract and Repel ∴ there are 2 parts (north & south)
– Opposites attract -- Like pole repel
Differences from Electricity
• You can get 1 e by itself. You can never get a
North pole without a South Pole and vice versa.
S NS N S N S N

3. Magnets & Electricity
• Electrons & magnetic fields
– Remember electron spin?
• Charge in motion causes a small magnetic field.
– Many electrons spinning in same direction
produces …
• Magnetic Domains
– Clusters of aligned electrons spinning in the
same direction
– How is a weak magnet different from a strong
magnet?
• Stronger magnets have more aligned domains

4. Magnetic Domains
How strong are these magnets? Why?

5. Magnetic Field (B)
 Area around a magnet that affects other magnetic objects.
Measured in Teslas (T)
Vector or Scalar?
N S
Rules for drawing
Leaves Object perpendicular
Out of North into South
more lines stronger field
Field is strongest at the poles
Magnetic Force caused by Magnetic Field
F = q v B
– qelectron & proton = 1.6 x 10-19 C

6. 1st Right Hand Rule
Direction of the magnetic force is perpendicular to
the velocity and the field
1st Right Hand Rule (3 Dimensions)
 Tells you the direction of the force.
• Place your fingers in the direction of B
• your thumb in the direction of v
• palm tells direction of the force
• out of + into –
Since this deals with 3 Dimensions…
mean going into the page (feathers of an
arrow)
mean coming out of the page (arrowhead)

7. • Find the direction of the force for each of
the following on a proton.
v B B
Bout
Bin
v
v
v

9. What direction would the force be on a proton with
velocity v in a field B?
Sketch the path of the electron once it enters the
magnetic field. Because it goes in a
circular path, the
magnetic force becomes
Bout the centripetal force
(sum of all the forces
pulling an object into a
v circle.)
FC = FM
m v2/R = q v B

10. What direction would the force be on a proton with
velocity v in a field B?
Sketch the path of the electron once it enters the
magnetic field. Because it goes in a
circular path, the
magnetic force becomes
Bout the centripetal force
(sum of all the forces
pulling an object into a
v circle.)
FC = FM
m v2/R = q v B