We take a slightly more indepth look at how power transformers work than the simple turns ratio equation relating input to output voltage. We discuss the inductance of the primary and observe the magnetizing current on an oscilloscope, as well as seeing what happens when the core goes into saturation. We also look at how the primary "knows" there is a load on the secondary and why current in a winding is reduced if the number of turns and hence voltage is increased. Finally we look at basic design compromises reacquired to decide how big or small a transformers is for any given load while keeping efficiency high and core and copper losses low.