I was referd to this forum from a friend and I have been reading some of them and I think you guys can help me and I would be very happy if you could. I was taking a electormagnitism physics class in school, calc based, and I had this idea for a project. I know that to calculate the magnetic field that is F=I*L*B*sin(thata) and the magnetic field of a solenoid is B=(u*n*I)/(2R) and n=turns/length. The question I have is how do I calculate the number of turns a solenoid needs when it has an iron core and what core to choose? I have been reading outside of class about fearite and iron powder cores and it seems they have a class for each but I don't understand them. I havn't even decided if I should use a tipical solenoid or a toroid either. I am trying to find out if I can make a electromagnet that is roughly 5" high, 11" wide, and 12" long(this may have to be shorter), that runs on 20 amps, 12-24V DC, and has a 25,000-60,000N pull force on it (would really like to hit that max but not being picky). I realize I have taken only one physics class about magnetics and this sound rediculus so if it can't be done it wont't hurt my fealings none. Thanks for any input.