Inductance

The Core Idea: Flux is Proportional to Current

Whenever a current flows through a coil, it creates a magnetic flux ($\Phi_B$) through that coil (or through a nearby coil). The key experimental observation is that this magnetic flux is directly proportional to the current ($I$) that produces it.

For a closely wound coil with $N$ turns, the same magnetic flux links every turn. Therefore, we talk about the flux linkage, which is $N\Phi_B$. This flux linkage is also proportional to the current:

Defining Inductance

The constant of proportionality in the relation $N\Phi_B \propto I$ is called inductance (symbol $L$). It is a scalar quantity that tells us how much flux linkage a coil produces for a given current.

From this, we can define inductance as:

Physical meaning: Inductance is a measure of a coil's opposition to a change in current. A coil with high inductance will produce a large induced emf for a given rate of change of current.

What Does Inductance Depend On?

Inductance depends only on:

1. The geometry of the coil (number of turns, area, length, shape).
2. The intrinsic material properties of the medium inside the coil (e.g., the magnetic permeability of a core material). …