waves

• Permanent magnet


  • Produces its own magnetic field
  • Magnetic forces are strongest at the poles
• Induced magnet


  • Becomes a magnet when placed in a magnetic field
  • Loses magnetism quickly when removed from the field
• Plotting magnetic field pattern of a magnet

  1. Use a compass

  2. Draw the magnetic field pattern of a bar magnet showing how strength and direction change
• Magnetic compass


  Points in the direction of the Earth's magnetic field
• The Earth has a magnetic field
• Magnetic field


  The region around a magnet where a force acts on another magnet or on a magnetic material
• The force between a magnet and a magnetic material is always one of attraction
• The strength of the magnetic field depends on the distance from the magnet
• The field is strongest at the poles of the magnet
• Direction of magnetic field

  Given by the direction of the force that would act on another north pole placed at that point
• Magnetic field lines go from the north (seeking) pole to the south (seeking) pole of a magnet
• Solenoid


  Increases the strength of the magnetic field created by a current through the wire
• Adding an iron core increases the strength of the magnetic field of a solenoid
• Electromagnet


  A solenoid with an iron core
• Demonstrating the magnetic effect of a current


  Draw the magnetic field pattern for a straight wire carrying a current and for a solenoid (showing the direction of the field)
• When a conductor carrying a current is placed in a magnetic field, the magnet and the conductor exert a force on each other (the motor effect)
• Fleming's left-hand rule


  Represents the relative orientation of the force, the current in the conductor and the magnetic field
• The size of the force on the conductor depends on the magnetic flux density, the current and the length of the conductor
• Loudspeakers and headphones


  Use the motor effect to convert variations in current in electrical circuits to the pressure variations in sound waves
• Induced potential difference/current


  Occurs when an electrical conductor moves relative to a magnetic field or if there is a change in the magnetic field around a conductor
• An induced current generates a magnetic field that opposes the original change, either the movement of the conductor or the change in magnetic field
• Transformer


  Consists of a primary coil and a secondary coil wound on an iron core
• Iron is used as it is easily magnetised
• Ratio of potential differences across primary and secondary coils of a transformer


  Depends on the ratio of the number of turns on each coil
• In a step-up transformer, the secondary voltage is higher than the primary voltage
• In a step-down transformer, the secondary voltage is lower than the primary voltage
• If transformers were 100% efficient, the electrical power output would equal the electrical power input