inductivity (L)
The inductance (L) is a frequency-dependent, passive electronic component whose inductive resistance increases with increasing frequency. The term inductance refers to the principle of magnetic induction or self-induction on which inductors, i.e. coils, are based.
When current flows through a coil, the magnetic field lines change in rhythm with the current flow. The magnetic field lines that occur whenever current flows create a mutual induction or self-induction in the coil itself. Such induction counteracts a change in the primary magnetic field, causing the current to increase exponentially while the voltage decreases exponentially.
Characteristics of inductors
The unit of measurement for inductance is the Henry (H), named after the American physicist (1797 to 1878), The Henry is expressed in volt- second/ ampere or ohm-second and can be derived from the System of Units( SI). An inductance of 1 Henry produces a self-inductance of 1 volt (V) in a coil with a uniform current change of 1 ampere (A) in one second (s). Smaller inductance values are given with the appropriate prefixes in millihenry, microhenry, and nanohenry.
The inductance of a coil depends on the number of turns, the cross-sectional area, the magnetic conductivity, the permeability, and inversely proportional to the coil length. Since permeability enters linearly into the magnitude of inductance, it can be increased accordingly by a coil core with higher permeability, such as a ferrite core.
Inductors do not have a real resistance, but a reactance. The inductive reactance (X(L)) of a coil is directly proportional to the magnitude of the inductance and the frequency. It therefore increases proportionally with higher frequencies. With direct current, the resistance of a coil corresponds to the conductor resistance.