Magnetic Field Strength of an Electromagnet given variable currents

[thehoyboy]

I had a lab to do for Physics, and we used a variable voltage source and an electromagnet with 60 turns of copper wire. What is the equation to use to find the magnetic field strength B using relative permeability of a soft iron core? i cannot find this equation anywhere... plus, what is the relative permeability constant for soft iron?

 

[Spinnor]

See 1/3 of the way down the following link.

http://en.wikipedia.org/wiki/Solenoid

Formula for both air core and magnetic core solenoid.