File:Laminated core eddy currents.svg

English: Diagram showing how a laminated core in a transformer prevents energy losses due to eddy currents. The alternating current in the transformer's winding creates an alternating magnetic field (B, green arrows) within the transformer's steel core. Since the core is electrically conductive, the field induces circulating loops of electric current in the core (red lines) called eddy currents due to Faraday's law of induction, which flow in planes perpendicular to the field. The current flowing through the resistance of the core dissipates energy as heat, causing energy losses. To reduce the power losses, instead of a solid core (left) many transformers use a laminated core (right). The core is made of a stack of thin steel laminations, with a nonconductive coating on the surface. The eddy currents can't cross from one lamination to the next, so the only eddy currents that can flow must flow within the thickness of each individual lamination. Since the magnitude of the current is proportional to the area enclosed by the loop, this reduces the eddy currents greatly and thus the energy lost in the core.