1. The problem statement, all variables and given/known data Electrons in crossed electric + magnetic fields: Simulation. I need to find e/m with known E, U and B. Easy way to find e/m is to set U, E and B such that I dont get any deflection of the electron beam. In that situation magnetic and electric force are equal -> E=B*v (v=speed of the electrons). I put that in eU=0.5*m*v^2 and I get e/m. Now, what if I did the experiment this way: PIC . There is a small deflection but lets approximate one segment with a straight line. How do I find e/m now? So, known data are U, E, B and slope of the deflection. 2. Relevant equations 0.5mv^2=eU (v = initial speed) F1= eE electric force F2 = ev x B magnetic force 3. The attempt at a solution I tried to calculate deflection only magnetic force would make and then deflection only electric force would make and then if I subtract those deflections it should be equal to the deflection of my straight line. Its not an easy way and Im not sure about my assumption?