inductance of a solenoid

[pattiecake]

A solenoid has 140 turns uniformly wrapped around a soft iron core, which has a magnetic permeability =750 Uo (mue sub-knot) diameter of 10.0m and a length of 9.00cm.

What is the inductance in milli-henry (mH)?

Did I set this up right? Using L=(uN^2A)/length, you get:

(750*140^2*pi.005m^2*.09m)/.09m = 1.15E3 Henry = 1.15E6 Milli-Henry

I think I made a conversion error somewhere. If not, why would they ask for the inductance in milli-henry, and not kilo-henry? :confused:

[Doc Al]

Your formula for L is correct. In your arithmetic I see two errors: an extra 0.09m on top, and--most importantly--a missing μ0. The permeability is μ = 750 μ0; μ0 = 4π10-7 N/A2.

[pattiecake]

ohhhhhhhhhhh! Thanks!