Inductance of Solenoid w/ Rod Inside: R, L, N, I, μ

[eric336]

A solenoid has a radius R, length L, with N turns and carrying a current I. If a cylindrical rod with permeability μ and radius R/2 is inserted inside the solenoid, what is the inductance of solenoid?

 

[tiny-tim]

hi eric336!

show us what you've tried, and where you're stuck, and then we'll know how to help!