A proton accelarted by a potential differnce `V` gets into the unifrom electric field of a paralallel-plate capacitor whose plates extended over a length `l` in the motion direction. The field strenth varies with time as `E = at`, where `a` is a constant. Assuming the proton to be non-relatistic, find the angle between the motion directions of the proton before and after its fight throgh the capacitor, the proton gets in the field at the moment `t = 0`. The edge effects are to be neglected.
