Transformers (Cambridge (CIE) O Level Physics): Revision Note

Transformer

• 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

Structure of a transformer consists of a soft iron core, and a primary and secondary coil

• 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

Step-up & Step-down Transformers

• 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)