• A transformer is used to raise and lower AC voltages
  • As a result, it raises and lowers current, but not power (unless inefficient)
  • It is simply two coils wrapped around a common soft iron core
  • It has a primary source, connected to the power source, and a secondary source which is connected to the load.

Only AC power can be used in a transformer.

This is because it changes direction of EMF, hence, a change in flux occurs.

This change in flux induces a magnetic field, which induces an EMF in the secondary coil

If DC power was used, there would not be any change in flux, hence no EMF produced.


  • Varying flux in a transformer produces eddy currents
  • They reduce the efficiency of the transformers
  • To prevent them, laminations are used


transformer equation


Poutput = P input assuming 100% efficiency

Inefficiencies only affect current

Voltage is unaffected ( in this course)


  • Electricity is produced by large AC generators
  • Two main concerns: minimising power loss, whilst supplying sufficient power

Power loss

P loss = ΔV I

Where ΔV = voltage drop of the cables during transmission, I = transmission current

P = I2 R

To reduce P loss, reduce I and R

  • That is, increase total EMF
  • This reduces transmission current, reducing power loss
  • OR reduce R by using more conductive material, large diameter cables, shorter cables

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