I found an old post with an almost identical question: https://www.physicsforums.com/showthread.php?t=54092 However, I still don't see how to work the problem. My question is phrased exactly the same, except B = 0.0170T and it's a 750eV electron. I have absolutely no clue how I'm supposed to relate eV to velocity, but I'm pretty sure (at least I read it somewhere on the web) I should be able to set 1/2mv^2 = eV. If I do this I end up with v = sqrt(2eV/m) = 4.06*10^16. Plugging that into the equation E = vB = 6.90*10^14. That's way off......... The answer should be kV/m, and from various friends that have gotten it right I hear it should be 3 digits (i.e. 100 <= answer <= 999). Can somebody give me a hint, help me along here? EDIT: I have another question in which I need to somehow related eV to velocity as well. This one is finding the radius of a cyclotron, given it's to accelerate to 32.0 MeV using magnetic filed 4.5T. I know r = mv / qB, so once again I'm missing v.