Question
A charge particle with charge q enters a region of constant E and B with velocity V perpendicular to both E and B, and comes out without any charge in magnitude or direction of V, then establish a relation between V, E and B.
Solution
A charged particle goes undeflected when,
qE = qvB
v = E/B
The force due to electric field and magnetic field are acting on the charged particle and will oppose each other if .
Now, v =
Therefore,
which is the required relation .