7.3 Induced Potential, Transformers and the National Grid

• Induced potential difference


  A potential difference induced across the ends of a conductor when it moves relative to a magnetic field
• Induced potential difference


  A potential difference induced across the ends of a conductor when there is a change to the magnetic field it is placed in
• Requirement for induced potential difference to cause current flow

  • The conductor must form a closed loop or be part of a complete circuit
• Direction of magnetic field produced by induced current

  • The direction of the field is such that it opposes the change that induced the current, which is either the movement of the conductor or a change to the field
• Ways the generator effect is used to generate different types of current

  • In an alternator to produce alternating-current
  • In a dynamo to produce direct-current
• Electromagnetic effect a microphone takes advantage of

  The generator effect, converting the pressure variations in sound waves into alternating current in a circuit
• Makeup of a basic transformer


  • A primary coil and a secondary coil of wire wrapped around an iron core
• Why iron is used as the core for a transformer

  It is easily magnetised
• How a transformer works

  1. An alternating current flows through the primary coil

  2. This induces a changing magnetic field in the core

  3. This changing magnetic induces a current to flow in the secondary coil
• Why the current flowing through the primary coil of a transformer must be alternating


  For current to be induced in the secondary coil, the magnetic field in the core must be continuously changing, and for the magnetic field to be changing, the current in the primary coil must be alternating
• For a 100% efficient transformer, the electrical power input is equal to the electrical power output