The document defines and describes an ideal transformer. An ideal transformer is defined as a transformer without any losses, meaning it has 100% efficiency. The ideal transformer model assumes windings are purely inductive with zero resistance and the core is lossless. This means 100% of the flux passes through the core and links both the primary and secondary windings. When an alternating voltage is applied to the primary winding, it induces a counter emf in the primary and draws a magnetizing current that lags 90 degrees. This current produces a flux that links the secondary winding and induces another emf in the secondary.