magnetism

• uniform field

  placing two permanent bar magnets creates a uniform field

  
• Motor effect

  A wire carrying a current creates a magnetic field.

  magnitude of force increases with the strength of magnetic field

  • current creates a magnetic field around the wire
  • field interacts with the external magnetic field
  • exerting a force on the wire

  increases the amount of current passing through the conductor
• electromagnets

  coils of wire with electricity passing through them
• an electric current in a conductor produces a magnetic field around it


  larger current = stronger magnetic field

  direction of the magnetic field depends on the direction of current
• Magnetic properties

  soft ie. iron

  • easy to magnetise
  • easy to demagnetise

  hard ie. steel

  • hard to magnetise
  • hard to demagnetise
• magnetic field lines

  always point north to south

  show the size and direction of the magnets fields
• What are the poles on a magnet

  north and south
• magnetic field

  region where magnetic materials experience a force
• magnetism induced

  ie. paperclips

  if you bring a permanent magnet close to a magnetic material it becomes an induced magnet
• like poles repel

  
• like poles attract

  
• magnetic field around a straight wire

  field is made up of concentric circles with the wire in the centre
• magnetic field around a straight wire

  magnetic field around a straight, current-carrying ire
• magnetic field around a straight wire


  magnetic field around a straight, current-carrying wire

  field made up of concentric circle - with a wire in the centre

  
• magnetic field around a flat circular coil

  concentric ellipses (stretched circles) of magnetic field lines around the coil

  
• magnetic field around a solenoid

  strong and uniform

  outside the coil, the field is like one around a bar magnet

  ends of a solenoid act like the north pole and South Pole of a bar magnet

  called an electromagnet

  
• Investigate the magnetic field pattern for a permanent bar magnet and that between two bar magnets

  Magnetic fields can be mapped out using small plotting compasses:

  1. place the plotting compass near the magnet on a piece of paper
  2. mark the direction the compass needle points
  3. move the plotting compass to many different positions in the magnetic field, marking the needle direction each time
  4. join the points to show the field lines
• Describe the four ways to increase the strength of an electromagnet

  • Increase the current
  • Increase the number of turns in the solenoid, while keeping the length the same
  • Reduce the length of the solenoid while keeping the number of turns the same
  • Add a soft iron core
• electric currents produce their own magnetic field
• Where is the magnetic field strongest?

  where they are close together
• What does the direction of the magnetic fied depend on

  direction of the current
• electromagnets

  only magnetic whilst current flows through the wire
• How do you reverse the direction of the electromagnet

  reverse the direction of the current