8.2 Inductors and Flux Density

Here's the second installment of Module 8, Induction, in Navy Basic Electricity and Electronics series from the 1970s. The first unit was:

8.1 Electromagnetism

1. Flux density is the strength of a magnetic field around something, for example a coil. There are four factors that directly affect flux density and one that inversely affects it.

2. The first factor is the "permeability" or "reluctance" with which magnetic flux can pass through a material. If the core of a coil is an iron rod (more permeable), then there will be a significantly greater flux density of the magnetic field than if the core is simply air (, say with the coil wrapped around a cardboard cylinder.

The symbol for an inductor with either an iron core or an air core is as follows:

iron core conductor                            air-core conductor

3. The second factor that increases flux density is the number of turns in the coil. The more the turns, the greater the magnetic force.

4. The third is the cross-sectional area of the core. The bigger the cross-section, the greater the flux density. This is the opposite of the fifth factor, which is the length of the core. The longer the core, the less the flux density.

5. Finally, the amount of current flowing through the coil directly affects the flux density. The more the current, the greater the flux density.