Magnetism
Magnet Facts
Two ends (poles) one is north the other is south
Types: can be bar, horseshoe, circular shaped, whatever the shape they always have a N and S pole
If you cut a magnet the new pieces will each have a N and S pole, no matter how small the pieces get
Magnetic forces involve attraction and repulsion
RULE: Like poles repel, unlike poles attract
Magnetic Fields
Book Definition: A magnetic field, represented by lines of force extending from one pole to the other, is an area over which the
magnetic force is exerted
What it means: Region in which the magnetic forces can act, the force is strongest at the poles
Lines of force in a bar magnet
The lines of force of a magnet are imaginary lines used to illustrate and describe the pattern of the magnetic field
Magnetic Materials:
Iron, Nickel, Steel, Cobalt: heavy metals are magnetic
Lodestone or Magnetite is naturally magnetic stones
Ferromagnetic materials are strongly attracted to magnets and can be made into magnets. Ex: Iron Nails
Temporary magnets (one you can make) remain magnetized for a short time
Permanent Magnets are difficult to make but they remain magnetized for a long time
Lodestone
Explanation of Magnetism
Magnetic properties depend on atomic structure
Atoms join in a way so their magnetic fields all line up the same way (aligned), the north’s all face one direction and the south’s
face the other direction
Magnetic Domain: region where the atoms are lined up together
Unmagnetized materials have domains that are arranged randomly, when the domains get aligned a magnet is formed
If the domains get out of order then the object will lose its magnetism (dropping it, heating it)
Earth as a magnet:
William Gilbert: proposed that Earth is a magnet and the poles are magnetic
Earth does behave like it has a huge bar magnet buried deep in it. It is believed to be related to the motion of the outer core which
is made of mostly iron and nickel.
The Earth exerts magnetic forces and is surrounded by a magnetic field that is strongest near the north and south magnetic poles
Proof: As rock undergoes changes (metamorphism) it liquefies and the mineral particles line up in the direction of the Earth’s
magnetic poles. As the rock cools and hardens there is a permanent record of the Earth’s magnetism.
There are stripes within rocks that show the direction of the poles, the stripes have revealed that the poles reverse themselves
every half million years or so.
What it does:
The Earth's magnetic field is important because it shields the Earth from a large percentage of cosmic rays (the field focuses these
rays towards the poles and away from other latitudes). The field is also used by many organisms to navigate.
During reversal times, things would probably go haywire with electronic communications and other electronic devices due to
bombardment by more cosmic rays in low latitudes. Animals may also have trouble navigating.
Basically no one is sure, electronics would not function properly and animals may get “lost” and die from exposure to the
elements, compasses would not point to the north.
Magnetism in action
If a charged particle moves in the same direction as a magnetic field, no force is exerted on it (won’t move). If a charged particle
moves at an angle to a magnetic field, the magnetic force acting on it will cause it to move in a spiral around the magnetic field
lines.
Solar Wind: Wind of charged particles (ions) sent out from sun (500 km/sec), the particles are deflected by the Earth’s magnetic
field called the magnetosphere
Aurora’s: When the ions get close to the earth’s surface they interact with atoms causing the air to glow. The glowing region is
called an aurora.