Which type of transformer core assembly provides low resistance to magnetic lines of force?

The type of transformer core assembly that provides low resistance to magnetic lines of force is iron. Iron is a ferromagnetic material, meaning it can easily conduct magnetic fields due to its high permeability. This property allows magnetic lines of force to travel through the iron core with minimal resistance, enhancing the efficiency and performance of the transformer.

Iron's magnetic characteristics enable it to efficiently channel the magnetic flux generated by the current flowing through the transformer windings. This results in better energy transfer and reduced losses, which is critical in electrical applications. Using materials such as aluminum or copper would not provide the same level of magnetic efficiency as iron due to their lower magnetic permeability. Plastic, on the other hand, is non-magnetic and would not serve effectively as a core material for transformers where magnetic properties are essential.