Inductance is a property of all electrical conductors. It is a measurable quantity; therefore, it has a physical dimension, a measurement unit (the henry), as well as reference standards. It is found as self-inductance L of a single conductor and as mutual inductance M in the case of two or more conductors. Inductors can vary in construction, but windings in the form of coils are the most frequent. In this case, they have specific geometrical parameters: surface A, length l, and a number of turns of windings N. The path of magnetic flux can be specially shaped by magnetic cores. Figure 30.1 shows examples of different inductive elements of electrical circuits.