1. The problem statement, all variables and given/known data Hydrogen ions moving at various speeds are directed at a region of combined electric and magnetic fields as shown in the diagram below. The electric field is between two parallel plates 10 mm apart with a potential difference V across them, while the magnetic field of flux density 0.1 T is at right angles to the electric field. (a) Calculate the value of V required so that ions of speed 100 m s-1 pass through the region of the two fields without being deviated. (b) What is the kinetic energy per ion as they leave the combined fields? (1 u = 1.67 * 10-27 kg.) Answers: (a) 0.1 V, (b) 8.4 * 10-24 J. 2. The attempt at a solution (a) Can't get it right. I use 0.5 m v2 = e V, where we don't know the mass m. I then tried to use F = B e v = 0.1 * 1.6 * 10-19 * 100 = 1.6 * 10-18 N and then F = m g so m = F / g = 1.6 * 10-18 / 10 = 1.6 * 10-19 kg -- not correct. I also used B e v = m v2 / r so m = B e r / v = 0.1 * 1.6 * 10-19 * 0.01 / 100 = 1.6 * 10-24 kg. Also not correct. I even thought that since we have hydrogen then its relative atomic mass is 1.008 and so 1.008 * 1.67 * 10-27 = 1.68 * 10-27 kg, also not correct. If we plug in 0.1 V (which we need to find) into the first formula we'll get m = 3.2 * 10-24 kg. But I've got no idea how to find it.