Transformers (CIE IGCSE Physics)

• A transformer is a device used to change the size of an alternating voltage or current
  • 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

Construction of a simple transformer

A simple transformer is made up of a primary coil and a secondary coil wound on a soft iron core

• A transformer consists of a primary and secondary coil
  • The primary coil is the first coil
  • The secondary coil is the second coil

Step-up transformer

• A step-up transformer: 
  • increases the voltage of a power source 
  • has more turns on the secondary coil than on the primary coil 

A step-up transformer has more turns on the secondary coil which increases the size of the voltage

Step-down transformer

• A step-down transformer: 
  • decreases the voltage of a power source 
  • has fewer turns on the secondary coil than on the primary coil 

A step-up transformer has fewer turns on the secondary coil which decreases the size of the voltage

Extended tier only

• 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 an emf (voltage)

• As the magnetic field is continually changing, the induced emf will be alternating
  • The alternating emf 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