Transformers can also be used to increase the voltage. In the transformer below, the secondary coil has more turns than the primary.
The changing magnetic field inside the iron core has more effect on the secondary coil, so a larger voltage is induced across it than is applied across the primary.
So hang on a minute - are we getting something for nothing? Sadly, no! Vs will be bigger than Vp, but the energy that we put in to the transformer cannot be less than we get out. More on this later.