Self Inductance of a Solenoid Problem

[liamporter1702]

Homework Statement

Hi again guys, been stuck on this problem for a while now, thought it would be a simple bumping in some values in a given equation question but I can't get the correct answer Heres the problem:

What is the inductance of a 600 turn coil wound on a core of cross sectional area 450mm² , length of 500mm and a relative permeability of 25?

Homework Equations

I assumed the equation I would use would be L=μ₀μ_rn²Al
Where n = number of turns
A = cross sectional area
l = length
μ₀ I took as 12.6x10^-7
and μ_r = 25

The Attempt at a Solution

When I put all these values into the equation I get 2.55, where as the given answer is 10mH. I'm stumped

 

[Andrev]

The correct equation is: $$L=\frac{\mu_0 \mu_r n^2 A}{l}$$