Transformers (CIE IGCSE Physics)

• A transformer is an electrical device that can be used to increase or decrease the potential difference of an alternating current (voltage transformations)
  • This is achieved using the generator effect

• A basic transformer consists of:
  • A primary coil
  • A secondary coil
  • A soft iron core

• Iron is used because it is easily magnetised

Structure of a transformer

EXTENDED

• An alternating current is supplied to the primary coil
• The current is continually changing direction
  • This means it will produce a changing magnetic field around the primary coil

• The iron core is easily magnetised, so the changing magnetic field passes through it
• As a result, there is now a changing magnetic field inside the secondary coil
  • This changing field cuts through the secondary coil and induces a potential difference

• As the magnetic field is continually changing the potential difference induced will be alternating
  • The alternating potential difference will have the same frequency as the alternating current supplied to the primary coil

• If the secondary coil is part of a complete circuit it will cause an alternating current to flow

• A transformer consists of a primary and secondary coil
  • The primary coil is the first coil
  • The second coil is the second coil
• A step-up transformer increases the potential difference of a power source
  • A step-up transformer has more turns on the secondary coil than on the primary coil (N_s > N_p)

• A step-down transformer decreases the potential difference of a power source
  • A step-down transformer has fewer turns on the secondary coil than on the primary coil (N_s < N_p)