Vocab
Magnetism
- The force of attraction or repulsion between magnetic poles
- Comes from the name Magnesia, a coastal district of Ancient Thessaly, Greece
- Unusual stones were found by the Greeks more than 2000 years ago
- These stones, called lodestones, had the intriguing property of attracting pieces of iron
- Magnets were first fashioned into compasses and used for navigation by the Chinese in the 12th century
What causes magnetism?
- The motion/spinning of electric charges
- Spinning like tops, the electrons circle the nucleus of an atom
- Their movement generates an electric current and causes each electron to act like a microscopic magnet
Earth's Magnetic Field
- Earth is itself a huge magnet
- Magnetic field produced from moving molten Iron core
- Movement is random and does change
Strength of Magnetic Force
- Depends on the distance between the two magnets
- Depends on the strength of the magnets
Magnetic Domains
- Microscopic pockets inside a metal where atoms align to face the same magnetic direction
- The more magnetized an object gets, the more organized the atoms get in the same direction
- When a magnet is broken into two pieces, each piece is an equally strong magnet
Earth's Changing Magnetic Field
- Earth's magnetic field reverses direction: 20 reversals in the last 5 million years
- Currently Earth's Geographic North is NOT the Magnetic North
Pole Interactions
- Like poles repel
- Opposite poles attract
Connection between Electricity and Magnetism
- Magnetic field forms a pattern of concentric circles around a current-carrying wire
- When current reverses direction, the direction of the field lines also reverse
Earth's Magnetic Field
- Storms on the Sun hurl charged particles towards Earth are trapped by its magnetic field
- Disturbances in Earth’s field often allow the ions to dip into the atmosphere, causing it to glow like a fluorescent lamp. Hence the aurora borealis or aurora australis
Magnetic Field
- Field lines always come out of the north pole and into the south
- The closer together the lines, the stronger the field
- The lines around a magnet are closest together at the poles because that’s where the magnetic force is strongest
Electromagnet
- An iron bar placed in a current carrying coil
- The most powerful electromagnets employ superconducting coils that eliminate the core
- Applications: Control charged particle beams high energy accelerators, lift automobiles and other iron objects, levitate and propel high speed "maglev" trains
Earth's Magnetic Field (Pt. 2)
- Universe is a shooting gallery of charged particles called cosmic rays
- Cosmic radiation is hazardous to astronauts
- Cosmic rays are deflected away from Earth by Earth’s magnetic field
- Some of them are trapped in the outer reaches of Earth’s magnetic field and make up the Van Allen radiation belts
Magnetic Poles
- All magnets can't have one pole without the other
- No single pole known to exist
- If a magnet is broken in half, each half gains a new pole
(Examples: Simple bar magnet and a horseshoe magnet where there are poles at the two ends)
Magnetic Forces on Moving Charges
- Moving charges in a magnetic field experience a deflecting force
- Greatest Force: Particle movement in direction perpendicular to the magnetic field lines
- Least Force: Particle movement other than perpendicular to the magnetic field lines
- No Force: Particle movement parallel to the magnetic field lines
Biomagnetism
- The generation, presence, or study of weak magnetic fields produced by living organisms
- Certain bacteria biologically produce single-domain grains of magnetite (a compound equivalent to iron ore) that they string together to form internal compasses.
- Example: Pigeons have multiple domain magnetite magnets within their skulls that are connected with a large number of nerves to the pigeon brain.