The expression for Lorentz force on electron is given by, F=q(E+v×B) The value of force becomes 0 when a body performs a regular motion. So, E+(v×B)=0 E∥(v×B), also (v×B) is perpendicular to both v and B Now, E⊥v and E⊥B. Then, E.v=0 and E.B=0 v.B=0 v⊥B So, E⊥v⊥B since, E=v×B E×B=(v×B)×B v×B=vB