Magnets

• Very few metals in the periodic table are magnetic

  • iron, cobalt, nickel are of the few that are magnetic
  • steel is an alloy that contains iron so it’s magnetic
• Magnetic materials in the periodic table

  A) iron

  B) steel

  C) cobalt

  D) nickel

  
• Testing for magnets - bring the material up to a known magnet

  • repels - magnet
  • only attracts, not repelled - magnetic material
• 2 types of magnets:

  • permanent magnet
  • induced magnet
• Permanent magnet

  • made out of permanent magnetic material e.g. steel
  • produces its own magnetic field
  • never loses its magnetism
• Induced/temporary magnet

  • happens when a magnetic material comes into contact with a magnet where it is temporarily turned into a magnet
  • When the magnetic material is removed from the magnetic field, it loses all of its magnetism or loses it very quickly - temporary effect
  • hard magnetic materials (such as steel, objects like paperclips) can be magnetised and stay magnetic for a while, losing their magnetism slowly
  • soft magnetic materials (such as iron, objects like iron nails ) instantly becomes demagnetised if the cause of the magnetism is removed
• Hard and soft describes the ability of the material to magnetise not the actual physical properties
• Ferromagnetics - materials that can hold magnetism well
• When magnetism is induced in a magnetic material, it becomes like a magnet

  • one end becomes the south pole and the other becomes the north pole
  • can also attract other magnetic material
• Magnetic materials are always attracted to a permanent magnet

  • the end of the magnetic material that is closer to the magnet will change poles to attract that magnet
• Magnetic material's interactions with magnets

  A) temporarily becomes south pole

  B) temporarily becomes north pole

  C) temporarily becomes north pole

  D) temporarily becomes south pole

  
• Most particles have tiny magnets

  • each electron and proton are tiny magnets
• Protons are weak tiny magnets, weaker than electrons

  • the nucleus having no effect on the magnetism of the atom
• Full shell atom: electrons generate a magnetic field due to their motion BUT it doesn’t create magnetism

  • electrons all move around equally, cancelling out their magnetic fields
  • tiny magnets of the pairs of electrons point in opposite directions, cancelling out
• Half-filled shells: have unpaired electrons and tiny magnets face the same direction, creating magnetism
• Full or close to full shells don’t have magnetism and half-full shells are magnetic e.g. nickel, cobalt
• A magnetic atom doesn’t mean the material made up of those atoms are magnetic

  • atoms align together → magnetic
  • atoms aligning in alternating fashion → not magnetic
• Domain - magnetic material may have aligned atoms but different areas of that material could not have atoms pointing in the same direction

  • these “domains” may not be strong enough to force another “domain” to align with them → no magnetism
  • applying a strong magnetic field near the material can force domains to align
• • Criterias of a magnet:
  • having a unified domain all pointing to the same direction
  • a domain made up of aligned magnetic atoms
  • atoms having half-filled outershells - electrons unpaired and tiny magnets face the same direction
• • Properties of magnets:
  • has a magnetic field
  • has two poles - north pole and south pole
  • like poles repel and unlike poles attract
  • attracts magnetic materials by inducing magnetism in the material
  • some materials have permanent magnetism while others have temporary magnetism
  • exert little or no force on non-magnetic materials
• Hammering, heating a magnet or using an AC current can demagnetize it by throwing the magnetic atoms out of line
• You can make a magnetise materials by stroking it with a magnet, using d.c. in a coil and hammering it in a magnetic field
• Alternating Current cannot be used to create a permanent magnet, as the direction of the magnetic field constantly changes with the change in current
• How to turn a steel rod into a magnet?

  Magnet is stroked along the rod repeatedly and the strokes are all in the same direction
• What are the differences between steel and iron?

   Soft iron loses magnetism easily while steel retains magnetism
• How do you make a compass using a: magnet, steel sewing needle, cork, and bowl of water?

  1. Repeatedly stroke the needle with a magnet in the same direction so it becomes magnetised
  2. Place the magnetised needle into a cork
  3. Now place this cork into a bowl of water