A beam of ions is deflected by the electric field between two plates 5cm apart with a p.d. pf 500 volts. It is found that this deflection is restored by a magnetic field of o.2T so that the ions continue in a straight line. What is their velocity (ions) ? So far I am thinking: upward force, F=qE E=v/d, 500V/ 5exp-2m = 1exp4 Vm^-1 Downward force F=mv^2/ r = Bev F= mv^2/r^2 I have some idea of what I need to do but some clarification would be great.