Question: how to calculate mmf in a coil?
Answer: Magnetomotive force (mmf), Fm = NI ampere-turns (At), where N = number of conductors (or turns) and I = current in amperes. Since 'turns' has no units, the SI unit of mmf is the ampere, but to avoid any possible confusion 'ampere-turns', (A t) are used in this chapter. where l = mean length of flux path in metres.