Induktance

Induktance is a property of an electrical conductor or component that opposes changes in the electric current flowing through it, due to the magnetic field that builds up around the conductor. It is quantified by the symbol L and measured in henries (H). When current changes, a voltage is induced according to Faraday’s law and Lenz’s law, producing an electromotive force that tends to oppose the change in current: e = -L di/dt for an ideal inductor.

Self-inductance refers to a single conductor or coil’s ability to induce a voltage in itself when its current changes. For a coil with N turns, the total magnetic flux linkage is λ = NΦ, and the inductance is L = λ / i. The energy stored in an inductor with current i is W = 1/2 L i^2.

Mutual inductance occurs between two coils that share magnetic flux. A changing current i2 in one coil induces an emf in the other coil: e1 = -M di2/dt, where M is the mutual inductance, depending on the geometry and the coupling between the coils. When both coils carry currents, the stored magnetic energy is W = 1/2 L1 i1^2 + 1/2 L2 i2^2 + M i1 i2.

Inductors are built with various core materials. Air-core inductors have low losses at high frequency, while iron-core or ferrite cores increase inductance in a compact form but introduce core losses and nonlinearity due to saturation.

In AC circuits, an inductor presents inductive reactance X_L = ωL, increasing with frequency and causing phase shifts between voltage and current. Real inductors exhibit parasitic elements such as equivalent series resistance and winding capacitance, which affect performance at high frequencies.

Applications include energy storage in power supplies, filtering and tuning networks, and transformers that rely on mutual inductance to transfer energy between circuits. Inductance is fundamental to many analog and RF systems.