Magnetism

Magnetism

1. magnetic materials

   • materials that can be attracted by/become a magnet
   • Steel
     • Hard material; Difficult to gain/lose magnetism; weak magnetic field strength in solenoid
   • Cobalt
   • Iron
     • Soft material; Easy to gain/lose magnetism; strong magnetic field strength in solenoid
   • Nickel

2. Properties

   • magnets have 2 poles (north n south), and forces are strongest at the poles
   • A freely suspended magnet comes to rest in north-south direction (north points to north pole)
   • Like poles repel, unlike poles attract

3. Magnetic Domains

   • Before magnetisation, domains are facing random directions
     • using magnetisation methods, domains all face same direction (hence got 2 poles)
       • Magnetisation methods
         • Induced magnetism
           • magnetic material becomes induced magnet when place in magnetic field (near magnet)
             • if put north side near material, it turns south
         • magnetisation using electricity
           • place material in a solenoid, polarities determined by direction of current
             • right hand grip rule
       • demagnetisation methods
         • Heating
           • heat magnet then cool in east-west direction (atoms vibrate n lose alignment
         • Hammering/dropping
           • hammer facing east-west. alters alignment of domains
         • pull out slowly of electric AC current
           • current facing east-west. will randomise magnetic domains)

4. Electromagnet vs Permanent Magnet

   • Electromagnet
     • coil of wire (sometimes with soft iron core)
       • Magnetism is temporary, requires current to sustain magnetism
   • Permanent Magnet
     • Hard magnetic material (like steel)
       • Permanent magnetism, do not need current

5. Magnetic Field

6. Magnetic Fields

   • region with magnetic field strength
   • Lines point towards south, coming out of north
     • between magnets
       • Like poles
       • unlike poles
     • magnetic shielding
       • uses magnetic material to divert magnetic fields, since the field will pass through the material
         • magnetic field cannot pass through magnetic material
     • strength is how close the lines are together

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