Magnetism and electromagnetism

• Magnetic materials; iron, nickel or cobalt; can be magnetized (made into a magnet)
• Hard magnetic materials are difficult to magnetize and demagnetize e.g. cobalt
• Soft magnetic materials are easy to magnetize and demagnetize e.g. iron
• Non Magnetic materials cannot be magnetized e.g. copper, zinc, non-metals
• Domains are small areas of magnetized material.
• In non magnetic materials domains are arranged randomly and cancel each other out.
• To magnetise a material the domains must be lined up in the same direction.
• Permanent magnets produce their own magnetic fields and are made from magnetically hard materials.
• Induced magnets are only magnets when placed in a magnetic field and are made from magnetically soft materials.
• One way of magnetising magnetic material is by stroking it with another magnet. You must stroke in the same direction so that all the domains line up.
• Another way of magnetizing a material is by leaving it next to another magnet for a while. Eventually the domains will move around and line up.
• One way of removing a magnets magnetism is by hammering it. The vibrations will let some of the atoms move around a little inside the metal so the domains can move around and point in different directions.
• Another way of removing a magnets magnetism is by heating the magnet.
• Two ends of a magnet are called north and south poles
• The poles are where the magnetic forces are strongest
• Like poles repel
• opposite poles attract
• If a magnet faces an unmagnetized magnetic material the forces are always attractive
• Magnetic forces are non-contact forces
• A magnetic field is where magnets experience a force acting on them
• The direction of a magnetic field line shows the direction of the force
• How close together the magnetic field lines are shows the magnitude of the force
• Field lines from magnets point from north to south