Magnetism & electromagnetism

• describe a magnet

  • has two poles north and south
  • produce a magnetic field
  • have magnetic field lines that go from north to south
• what do the magnetic field lines show us ?

  • the closer together the stronger the magnetic field
• where is the magnet the strongest ?

  at the poles
• what do the same poles do ?

  repel
• what do opposite poles do ?

  attract
• what is a permanent magnet ?


  a magnet that has its own magnetic field
• what is an induced magnet ?

  a magnetic material that turn intona magnet when in another magnetic field
• describe a compass

  • have a tiny bar magnet
  • determine magnetic field lines
  • always point north, when they are not near another magnet
  • point to the earths own magnetic field
• describe an electromagnet

  • current flowing through a wire that has a magnetic field
  • field is made up of concentric circles perpendicular to the wire
  • changing current direction changes the magnetic field
  • strength varies on current & distance from wire
• what is the right hand rule ?

  • thumb- current direction
  • fingers- direction they curl is direction of field
• what is a solenoid ?

  a coil of wire with a current increasing magnetic field strength because field lines around each loop of wire line up with eachother
• what is the magnetic field strength like I nn side of a solenoid ?

  strong and uniform
• what is the magnetic field strength like outside of a solenoid ?

  like a normal bar magnetic
• how canyou increase the strength of a solenoid ?

  add an iron core to become an induced magnet
• where are the poles of the solenoid ?

  at the end of the coil
• describe the motor effect

  a current carrying wire is put between magnetic poles the field interacts with the wire causing them to exert a force on eachother causing the wire to move
• how can the motor experience the full force ?

  • they must be at 90° to a magnetic field
  • forces always act in a right angles to the magnetic field
• how can you increase the force on a motor ?

  • strength of the magnet
  • amount of current
• what is magnetic flux density ?

  how many field lines there are in a region
• what is the left hand rule ?

  • thumb- direction of force
  • first fingers- direction of magnetic field
  • second finger- direction of current
• describe an electric motor

  1. coil is on a spindle and the forces act up and down causing it to rotate
  2. split ring commutator swaps contacts every halfturn to keep rotating in the same direction
• how can the rotation be reversed ?

  • swapping polarity of DC supply (current)
  • swapping the poles
• how can you increase the rotation ?

  • increase current
  • adding more turns to a coil