|MLA Citation:||Bloomfield, Louis A. "Question 239"|
How Everything Works 23 Apr 2018. 23 Apr 2018 <http://howeverythingworks.org/print1.php?QNum=239>.
A step-up transformer has a secondary coil with many, many turns. As the current in the primary circuit flows back and forth, it creates a reversing electric field around the iron core of the transformer. This electric field pushes charges through the secondary coil so that it travels around and around the core. Each charge goes around many times, picking up more energy with each passage. By the time the charge leaves the transformer, it has lots of energy so its voltage is very high.