1. The problem statement, all variables and given/known data A magnet is used to control negative ions and only allow those with a specific mass to pass through a narrow gap opening . The magnet will bend the ion beam in a quarter circle of radius 50 cm . In an experiment, a negative ion accelerated by a voltage of 3.0 kV. Which magnetic flux density must the magnets have for these molecules with mass 277 u to follow the circular path through the magnet and get through the gap opening ? 2. Relevant equations QU = MV ^ 2 * 1 / r , then mv ^ 2 * 1 / r = QVB 3. The attempt at a solution Because we have volt , I think QU = MV ^ 2 * 1 / r , then mv ^ 2 * 1 / r = QVB But we do not have Q, or v. Thus I do not know how I solve this . Sorry for the English, but it seems the problem cant be solved?