Revise: Magnetism
Magnets and magnetic materials, domain theory, magnetic fields, magnetisation and induced magnetism, and the magnetic properties of iron and steel.
Like poles repel; unlike poles attract. Ferromagnetic: iron, nickel, cobalt.
Magnetic separators pull steel cans from mixed recycling.
Domains aligned = magnetized. Domains random = unmagnetized.
Stroking a nail with a magnet aligns its domains.
Field lines: north to south outside the magnet, never cross.
A compass aligns with the Earth's magnetic field.
Induced magnetism is temporary — disappears when the magnet is removed.
A chain of paperclips falls apart once away from the magnet.
Iron: soft, easy on/off. Steel: hard, retains magnetism.
Iron cores for electromagnets; steel for compass needles.
Most materials (wood, plastic, copper) are not magnetic at all.
Two N poles facing each other repel.
Every material has domains — magnetizing aligns them, it does not create them.
Dropping a magnet disturbs its domains, weakening it.
Closer field lines = stronger field.
Field is strongest near the poles of a bar magnet.
Demagnetise by heating or hammering — disturbs domain alignment.
A magnetized screwdriver loses magnetism when hit repeatedly.
"Harder to magnetize" does not mean "weaker magnet" once magnetized.
Steel holds its magnetism far longer than iron.