1. Magnetism Notes
CP Physics
Ms. Morrison

2. General Information
Greeks discovered magnetic rocks called lodestones more than 2000 years ago
Chinese used lodestones to help navigate ships
Lodestones contain iron ore (magnetite)

3. Magnetic Poles Regions of the magnet that produce magnetic force
Pole pointing northward – North
Pole pointing southward – South
Breaking a magnet in half will not separate the poles – only makes two smaller magnets

4. Magnetic Poles vs. Electric Charges
Property
Magnetic Poles
Electric Charges
likes repel, opposites attract √
force acts over a distance
can separate charges (poles) from each other NO

5. Magnetic Fields
Space around a magnet through which magnetic force is exerted, can be seen with iron filings (shows magnetic field lines)
Magnetic field lines move from north to south pole
More lines = stronger field
Field strongest at poles

6. Magnetic Fields, pg 2
Moving charges create magnetic fields, ex. Spinning electrons
Electrons = tiny magnets
Pair spin in same direction = stronger magnet
Pair spin in opposite direction = no magnet because their magnetic fields cancel out

7. Magnetic Fields, pg 3
Most materials NOT magnetic because electron pairs cancel out their magnetic fields
Iron, nickel, and cobalt – have atoms with unpaired electrons whose magnetic fields are not entirely canceled out – so have magnetic properties
Iron has four unpaired electrons so each iron atom is a tiny magnet

8. Magnetic Domains
Large clusters of aligned atoms – their magnetic fields are so strong that they line up with each other
Magnets have domains that are lined up while ordinary iron and other materials do NOT have aligned domains

9. Magnetic Domains, pg 2
Can create permanent iron magnets by placing the iron in a strong magnetic field
Can create temporary magnets by placing materials with iron in them near a strong magnetic field, once field gone domains will revert to original state
Can destroy permanent magnets by dropping them or heating them up – causes domains to be jostled out of alignment

10. Magnetic Domains, pg 3

11. Electric Current and Magnetic Fields
Moving charges produce magnetic fields
Current through a wire creates a magnetic field around the wire – Oersted (1820)
Reversing current flow reverses direction of the magnetic field

12. Electromagnets A current-carrying coil of wire with many loops
Has a north pole and a south pole
Strength of electromagnetic affected by three factors
# of loops in the coil (more loops = stronger)
Amount of current (larger current = stronger)
Presence of iron core (present = stronger)

13. Magnetic Forces and Charged Particles
Charged particles at rest are not affected by magnetic field (stationary)
When moving, charged particles are deflected by magnetic fields
Used in TV tubes to create picture on screen
Earth’s magnetic field deflects charged particles from outer space (cosmic rays)

14. Magnetic Forces and Current-Carrying Wires
Current-carrying wire placed in magnetic field is deflected
Reversing current cause deflection in opposite direction
Greatest deflection occurs when current is perpendicular to magnetic field

15. Meters Meters use magnetic needle
Current moving through wires in meter creates magnetic field that interacts with magnetic field of needle
Cause needle to be deflected (like repel, etc.)
Amount of deflection indicates amount of current

16. Motors
Motors
Electric current through coil of wire inside a permanent magnet
Coil of wire creates magnetic field that interacts with magnet and begins spinning
Current must reverse every half turn so that two magnetic fields keep repelling each other
So electrical energy is converted into mechanical energy

17. Earth’s Magnetic Field
Earth is huge magnet (magnetic poles not same as geographic poles)
Thought to result from moving charges within molten part of Earth beneath crust
NOT stable – wanders, diminishes to zero and then reverses itself
Holds Van Allen Radiation belts around Earth (aurora borealis)