ELECTROMAGNETISM

Electromagnetism – Remember it!

Electromagnetism – Remember it!

  • Physics GCSE science revision- ElectromagnetismA region where a magnetic force is being exerted is known as a magnetic field.
  • Opposite poles attract, like poles repel.
  • Magnetic field lines run from north to south.
  • The catapult effect is due to the magnetic force cancelling out forces which are moving in the opposite direction to the magnetic field lines.
  • If a current passing through a wire in a magnetic field exerts a force on the wire this is called the motor effect.
  • The force can increased by using stronger magnet or increasing the current.
  • The size of the force depends on the angle at which the magnetic field lines and the wire.
  • Physics GCSE science revision- ElectromagnetismAn electric motor uses the motor effect and its speed can be altered by changing the current.
  • The armature coil of an electric motor is forced to rotate when a current passes through it.
  • Each half-turn the direction in which the coil is traveling is reversed by the split ring commutator.
  • A generator is composed of coils of wire that rotate within a magnetic field.
  • In a complete circuit the creation of a potential difference leads to an electric current which is able to travel through the circuit.
  • If an piece of insulated wire is connected to an ammeter then moved between the poles of a U-shaped magnet a current is produced each time the magnetic field line is cut by the wire. This is called the dynamo effect.
  • Forcing a rectangular coil to rotate within a magnetic field it’s possible to make a simple alternating current (AC) generator.
  • Physics GCSE science revision- ElectromagnetismA National Grid transformer is made from an iron core around which is wound two insulated wire coils: the primary coil and the secondary coil.
  • As an alternating current travels through the primary coil this induces an alternating potential difference in the secondary coil which produces a current.
  • A transformer only uses an alternating current because an alternating secondary potential difference can’t be created by a direct current.
  • The potential difference is increased when transferred from the power station to the National Grid by step-up transformers.
  • The potential difference is decreased when transferred from the National Grid to the mains by step-down transformers.
  • The secondary potential difference is dependant on the primary potential difference as well as the number of turns on both of the coils.
  • VP/VS = NP/NS
  • In a step-up transformer: VS is more then VP and NS is more than NP.
  • In a step-down transformer: VS is less then VP and NS is less than NP.
  • If a transformer is 100% efficient: IPVP = ISVS