Transformers

• Describe the makeup of a basic transformer.

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

  It is easily magnetised.
• Explain how a transformer works.

  • An alternating current flows through the primary coil
  • This induces a changing magnetic field in the core
  • This changing magnetic field induces an electromagnetic field, which produces a current in the secondary coil
• Why must the current flowing through the primary coil of a transformer be alternating?


  • For current to be induced in the secondary coil, the magnetic field in the core must be continuously changing
  • For the magnetic field to be changing, the current in the primary coil must be alternating
• What can be said about the electrical power input and output of a 100% efficient transformer?

  The electrical power input is equal to the electrical power output.
• Give an equation linking number of turns with potential difference in transformers

  Primary potential difference/ Secondary potential difference = Primary turns / Secondary turns
• State the power equation for transformers with a 100% efficiency (using voltage and current)

  Vp x Ip = Vs x Is

  Primary voltage x Primary current = Secondary voltage x Secondary current
• On a step-down transformer, does the secondary coil have more or fewer turns?

  The secondary coil has fewer turns.
• What is an advantage of a step-down transformer in the national grid?

  It means that the voltage can be reduced to a value safe enough to be used in homes.
• Why is it important to have a step-up transformer in the national grid?

  It can increase efficiency.

  • For the same power, a higher voltage will lead to a lower current (P = V x I)
  • The lower the current, the less energy that is lost.
  • Used for transmission across power lines
• How does a step up transformer work?

  • The primary coil has fewer turns
  • An A.C current produced a magnetic field in the primary coil
  • The iron core passes the magnetic field to the secondary coil
  • The magnetic field induces a higher voltage in the secondary coil
  • Power is conserved, so this produces a lower current
• Where are step-up and step-down transformers used in the national grid?

  Step-up transformers are used at power stations, whilst step-down transformers are used domestically.