1. Electromagnetism and Magnetic Domains
21-2
Electromagnetism
and
Magnetic Domains

2. Current creates a magnetic field!
What is current?

3. Magnetic Field of a Current Carrying Wire
Concentric circles of a magnetic field form around a current carrying wire

4. Magnetic Field of a Current Carrying Wire
Right-hand rule shows direction of field

5. Magnetic Field in a Current Loop
Field formed by a loop can be found using the right hand rule
Inside of loop is always one direction
Outside of loop is always the opposite direction
Forms N and S pole

6. Magnetic Field in a Current Loop

7. Solenoids Several closely spaced parallel loops
Fields of individual loops combine
Iron core is inserted to make field stronger
Electromagnet

8. Solenoids Right hand rule determines field
Fingers curl in direction of conventional current
Thumb points to N pole of solenoid

9. How Does Material Become Magnetized? Electrons (charged particles)
are in motion
Electrons also have a property
known as “spin”
In short, we’re not sure!

10. Magnetic Domains Magnetism is caused by the spin of electrons
Usually paired up and cancels out
Microscopic magnetic region composed of a group of atoms whose magnetic fields are aligned

11. Magnetic Domains
Hard magnetic materials the domain alignment resists change
Soft magnetic materials the domain alignment is easily changed

12. Has North Always Been North?
As we move out from the ridge, the magnetic domains alternate back and forth
The magnetic poles of Earth flip roughly every 250,000 years

13. What Happens When The Poles Reverse? It has been nearly
800,000 years since
the last pole reversal
What might be some
consequences if it
happens in your
lifetime?
Were the Aztecs
on to something???