Transformers

Imagine a power station is to supply power to a factory many miles away

A certain amount of voltage, and therefore energy, is lost due to the resistance of the power lines. We could use very thick copper cables but these are expensive. There is another solution.

A transformer can make an a.c. voltage bigger or smaller.

You should know enough about inducing emf's now to figure out how it works.

A step up transformer increases the voltage and decreases the current

A step down transformer decreases the voltage and increases the current

Say we wanted to supply a power of 100W. This could be done at a small voltage with a large current in the supply lines OR this could be done at a high voltage with a small current in the supply lines. As the power loss in the supply lines = I ² R,  where R is the resistance of the lines, the latter option is clearly more efficient.

The voltage from the power station is stepped up (to 400,000V on the national Grid) before it is transmitted. It is stepped down to 240V before it is supplied to houses for safety reasons.