how to build a strong electro magnet?
for my project, i would like to build a strong round electro magnet. i would like to know how i can build one.. i mean number of turns, current, diameter of wire. can we connect the coil to main power supply directly? i need a very strong magnetic field, one of my purpos is to levitate another magnet with out any support of strings (freely suspending in air).
thanx in advance.