Magnets are dipole objects

They:

• Create a magnetic field around it
• B: magnetic field strength (measured in Tesla)
• Magnetic field created by a bar magnet is not uniform

magnetic field and effects

• A magnetic field is the region around a magnet or current-carrying conductor where magnetic forces act on other magnets, magnetic materials, or moving charges

• Magnetic fields have direction and strength

• The direction of a magnetic field is defined as the direction a north pole would move

• Magnetic field lines:

  • Travel from north to south
  • Never cross
  • Are closer together where the field is stronger

• A bar magnet produces a symmetrical field pattern:

  • Field lines curve around the magnet
  • Lines are densest at the poles, showing strongest field strength
  • Arrows must always point from north to south when sketching

• When two bar magnets are placed near each other:

  • North–north or south–south orientations cause repulsion
    • Field lines bend away from each other
    • The region between magnets has a weaker field
  • North–south orientation causes attraction
    • Field lines connect directly between poles
    • The field between magnets is strong and concentrated

magnetic fields producing an electric current

• An electric current always produces a magnetic field around it

• This can be demonstrated by:

  • Placing a compass near a straight current-carrying wire
  • When current flows, the compass needle deflects, showing a magnetic field is present

• For a straight wire, the magnetic field:

  • Forms concentric circles around the wire
  • Has a direction given by the right-hand grip rule
    • Thumb points in the direction of conventional current
    • Fingers curl in the direction of the magnetic field

• For a single coil of wire:

  • The circular fields from each loop combine
  • The overall field resembles that of a bar magnet
  • One side behaves like a north pole and the other like a south pole

• For a solenoid:

  • The magnetic field inside is strong and uniform
  • The field outside is much weaker
  • The solenoid behaves like a strong bar magnet with clear poles

• The magnetic effect of a solenoid is increased by:
  • Increasing the current through the coil
  • Increasing the number of turns of the coil
  • Inserting a soft iron core, which becomes magnetised and strengthens the field

electromagnets