1. Textbook: 8.1 – 8.2 Homework: pg. 391 #1, 2, 7
Magnetism
Textbook: 8.1 – 8.2
Homework: pg. 391 #1, 2, 7

2. What do we know about magnetism?
LEDs
Incandescent lights
What do we know about magnetism?
- They have poles
- Opposite poles attract, similar poles repel
- It is an action-at-a-distance force (therefore can be described in terms of fields)
- One of the oldest known forces (magnetite was a naturally occurring magnet)
- Is used for navigation (Earth’s iron core creates a magnetic field aligned in the NS direction)
What are some properties of magnets?
- Things can be magnetized and demagnetized
- When a magnet is broken in half it makes two smaller magnets
- Some objects when magnetized maintain the field, others do not
- Heating, dropping and striking a magnet can demagnetize it
- A strong magnetic field can reverse the direction of a bar magnet

3. Domain Theory
Ferromagnetic materials can be magnetized (ex. Iron, nickel, cobalt)
Ferromagnetic materials are made up of tiny magnetic domains which act like miniature magnets
If, on average, the magnetic domains align they create an induced magnet
Explain using the domain theory:
- How an object can be magnetized
- Note: Some ships hulls, buildings become magnetized due to Earth’s magnetic field and constant vibrations
- How an object can be demagnetized
- Why some materials hold on to an induced field and others do not

4. Electromagnetism
Oersted’s Principal: A moving electric current induces a magnetic field
The direction of the induced electromagnetic field can be determined using the Right Hand Rules.
Ex. How does this help explain the domain theory of magnetism?
Ex. RHR - Straight Conductor
Ex. RHR - Loop of Wire
Ex. RHR - Solenoid

5. RHR for straight conductor
RHR for solenoid

6. Relative permeability: is the ratio of the magnetic field strength for a particular core material to the magnetic field strength in the absent of the material.

7. Magnetic Force on Moving Charges

8. Draw the magnetic fields of the permanent magnet and the conductor.
Determine the direction of the force on the conductor.

9. Show the labels of the magnetic poles, the magnetic field, and the direction of force on the conductor

10. Describe the path of current through the conductor, brushes, commutator, and coil by adding arrows. Identify the magnetic polarity of the armature and the rotation direction of the motor.