topic 12 and 13 physics

• Magnetic poles


  Unlike poles attract, like poles repel
• Permanent and temporary magnetic materials

  • Cobalt
  • Steel
  • Iron
  • Nickel
• Permanent magnet


  Retains its magnetism
• Induced magnet


  Becomes magnetic when placed in a magnetic field
• Magnetic field around bar magnets and uniform field


  • Shape and direction
  • Strength related to concentration of lines
• Using plotting compasses


  Show shape and direction of magnetic field of a magnet and Earth's magnetic field
• Behaviour of a magnetic compass

  Evidence that the core of the Earth must be magnetic
• Showing a current can create a magnetic effect


  Relate shape and direction of magnetic field around a long straight conductor to direction of current
• Strength of magnetic field around a long straight conductor

  Depends on size of current and distance from conductor
• Magnetic field inside a solenoid

  • Fields from individual coils add together to form a very strong almost uniform field along the centre
  • Fields from individual coils cancel to give a weaker field outside the solenoid
• A current carrying conductor placed near a magnet experiences a force, and an equal and opposite force acts on the magnet
• Magnetic forces


  Due to interactions between magnetic fields
• Fleming's left-hand rule


  Represents the relative directions of the force, the current and the magnetic field for cases where they are mutually perpendicular
• Factors affecting size and direction of induced potential difference


  • Magnetic field produced opposes the original change
• Transformer


  Can change the size of an alternating voltage
• Electrical energy transferred at high voltages from power stations


  Then transferred at lower voltages in each locality for domestic uses to improve efficiency by reducing heat loss in transmission lines
• Use of step-up and step-down transformers in the national grid

  1. Step-up transformers used to increase voltage for efficient transmission

  2. Step-down transformers used to decrease voltage for domestic use