If I have an air cored inductor which has an inductance of 100mH, and I insert a core with a permeability of 5000, what will my inductance be?

I know the inductance depends on a variety of things, but I'm just looking for a ball park figure (basic way) of estimating inductance whena core of a certain permeability is inserted into an air core inductor.

 

Since inductance is directly proportional to the relative permeability of the core, I would say your new inductor should now have 5,000 times the inductance of the air-cored value.

However, note the following from Wiki about the permeability w.r.t. current.

Note that since the permeability of ferromagnetic materials changes with applied magnetic flux, the inductance of a coil with a ferromagnetic core will generally vary with current.

 

Since inductance is directly proportional to the relative permeability of the core

Only true for 'close wound' components. That means the core has to pull the majority of flux into itself.

 

Also, the core has to have the same diameter as the coil's diameter to say that the inductance will be multiplied by about 5000.

 

That only works in closed or learly closed magnetic loops (a gapless core like a toroid is one example). The actual inductance is greatly affected by magnetic path length and core cross section as well as the permeability of the core.

The answer to your question is "Higher."

 

That only works in closed or learly closed magnetic loops (a gapless core like a toroid is one example). The actual inductance is greatly affected by magnetic path length and core cross section as well as the permeability of the core.

The answer to your question is "Higher."

This is actually a very good answer.


I might add that inductors that change permeability with current are NON-linear devices (saturable reactors). This property can be either HIGHLY undesirable, as in R.F. linear amplifiers, or quite useful, as in magnetic amplifiers.

In most R.F. applications, special care is taken to AVOID operating the core in the non linear region....the transmission line transformer is just one such application.

Eric