Transformers can also be used to ?step-up? voltages and are used in this way in power stations where they convert the 25kV they produce to 400kV so it can be sent across the national grid. The grid uses 400kV as there is less energy lost at these high voltages.

Transformer kits are available from lab suppliers and usually consist of 'C' cores, (C-shaped steel laminated sheets fused together) clips for securing two cores together and insulated copper wire. Small low voltage lamps may also be included.

After clipping the two cores together, wire is wrapped around each side of the core. In simple dual winding transformers, these are called primary and secondary coils. The ratio of the primary to secondary voltages is directly proportional to the number of turns in the primary and secondary coils. For example, in Fig 1 The primary coil has 5 turns and the secondary 10. If 1V is put through the primary coil then 2V will emerge from the secondary.

To step the voltage down the same principle is used but in reverse. A higher number of turns on the primary coil than on the secondary will effectively reduce the output voltage.

Fig 2 shows the relationship between voltage and current in and out in both types of transformer.

Pupils may need to experiment with different numbers of turns and so you may go through a large amount of solid core insulated copper wire. This is fairly inexpensive however to purchase by the reel from Rapid or Maplin.

A.C (alternating current) power must be used when connecting to a transformer. D.C power may cause the insulated wire to overheat and melt and may damage the core.