Is there a way of calculating how much force can be applied to an object if you are given the magnetic field strength of an electromagnetic? For example, if an electromagnet produces a B field of 4T, what is the maximum mass of iron it can hold? And also, how does one calculate the magnetic field outside of a solenoid? *edit* It seems that I may have another question...*sigh* If I wrap wires around an iron core like a solenoid to make an electromagnet, would its magnetic strength decrease or increase if I increase the radius of the core? How would I maximize the strength other than having more turns of wires?