Electrical Engineering ⇒ Topic : Factors affecting inductance

Factors affecting inductance. The greater the self-induced voltage, the greater the self-inductance of the coil and hence larger is the opposition to the changing current. According to

Faraday 's laws of electromagnetic induction, induced voltage in a coil depends upon the number of turns (N) and the rate of change of flux (dΦ/dt) linking the coil. Hence, the inductance of a coil depends upon these factors, viz :

(i) Shape and number of turns.

(ii) Relative permeability of the material surrounding the coil.

(iii) The speed with which the magnetic field changes.

In fact, anything that affects magnetic field also affects the inductance of the coil. Thus, increasing the number of turns of a coil increases its inductance. Similarly, substituting an iron core for air core increases its inductance.

It may be noted carefully that inductance makes itself felt in a circuit (or coil) only when there is a changing current Thus, although a circuit element may have inductance by virtue of its geometrical and magnetic properties, its presence in the circuit is not exhibited unless there is a change of current in the circuit. For example, if a steady direct current (d.c.) is flowing in a circuit, there will be no inductance. However, when alternating current is flowing in the same circuit, the current is constantly changing and hence the circuit exhibits inductance.

Note. The self-inductance of a coil opposes the change of current (increase or decrease) through the coil.This opposition occurs because a changing current produces self-induced e.m.f. (e) which opposes the change of current. For this reason, self-inductance of a coil is called electrical inertia of the coil.