Electric power transformers operate on electromagnetic induction. An alternating voltage applied to the primary winding produces a changing magnetic flux in the core. This time varying flux links to secondary windings and induces voltages proportional to the turns ratio. With a load connected, current flows, transferring energy from primary to secondary through the magnetic field. Ideally, power in equals power out minus small losses. By choosing appropriate turns ratios and insulation, transformers step voltages up or down efficiently while providing galvanic isolation between circuits.