# Frank Hertz I-V curve

Now my question is assume here gas to be hard balls with no possibility of inelastic collisions and electrons are emitted from a cathode and they reach anode through this soup of atoms. Since electrons are small enough, there probability of collisions should be small. Hence velocity of most electrons would be given by; 1/2mv2 = eV, we get a square root dependence on voltage, so the peaks of the curve must follow this trend but they don't, any explanation?