Consider a Proton Traveling with a Velocity V in the Presence

Multiple Choice

Consider a proton traveling with a velocity v in the presence of both an electric field E and a magnetic field B. If B $\times$ v is exactly equal to E, the Lorentz force (magnitude) acting on the proton is

A) 2 q E.
B) 2 q B v.
C) zero.
D) both (a) and (b) are correct answers.