Selfinductance

Self-inductance is a property of an electrical circuit that causes an electromotive force (emf) to be induced in the same circuit when its current changes. It arises from the magnetic field generated by the current, which links with the circuit’s conductors. The self-inductance L is defined by the flux linkage λ = L I, where λ is the total magnetic flux linking all turns and I is the current. The unit is the henry (H): 1 H = 1 V·s/A.

In an ideal inductor, the voltage and current are related by v = L di/dt. The energy stored in the magnetic field is W = (1/2) L I^2. In non-ideal coils, series resistance adds a term: v = L di/dt + iR.

Self-inductance depends on geometry and material. It increases approximately with the square of the number of turns N and with the magnetic permeability μ of the material inside the core, and with cross-sectional area A, while it decreases with the length l of the magnetic path. For simple geometries, L ≈ μ N^2 A / l for a long solenoid.

Self-inductance is a property of a single circuit, in contrast to mutual inductance M between two coupled circuits. In AC analysis, the inductor presents an impedance Z = jωL. Core materials can introduce nonlinearities due to saturation and losses.

Applications include energy storage in inductors, filtering and tuning in circuits, and impedance matching. The term self-inductance emphasizes that the inducing and induced effects come from the same conductor.