Question

can we determine the distance for an electron in a magnetic field ? I just have te velocity and the electric field value

Answer 1

hope this helps:
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/maspec.html

Answer 2

Do you mean magnetic or electric field?
Distance to what?

Answer 3

I´m sorry electric field the distance before the electron stop and returns

Answer 4

Use energy conservation. At closest range, KE will be zero and the remaining PE will give you the distance.