1. The problem statement, all variables and given/known data A system of spin 1/2 magnet moments with μ = 1*10^-23 Am² are in a magnetic field of 0.2T. At what temperature will 90% of the magnets be aligned parallel to B? 3. The attempt at a solution I think I have found the relevant equation: U=-μB(N↑ - N↓) where U is the magnetic potential energy, μ is the magnetic moment, B is the magnetic field, N↑ is the number of magnets oritentated up and N↓ is the number of magnets orientated down. My questions now are, how do I know which direction is parallel to B and if this equation is relevant, how do I then convert U to temperature?