Which symbol in Figure G7-1 represents a solid core transformer?

A transformer is drawn using two parallel inductor coils representing the primary and secondary windings. The material shown between these coils indicates the type of core used. Symbol 6 features two straight, solid parallel lines running between the coils, which universally denotes a solid iron or magnetic core. By contrast, if a transformer has an air core, there will be no lines drawn between the coils at all. If it features a powdered-iron or ferrite core, the lines between the coils are typically dashed. The solid lines in Symbol 6 explicitly identify it as a solid core device, commonly used for power or audio frequencies.