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.

Question

Quizplus · Accepted Answer

The Lorentz force acting on a charged particle in the presence of both electric and magnetic fields is given by $F = q(E + v \times B)$. If $B \times v = E$, then $E + v \times B = E + E = 2E$, but since they are equal and opposite in direction, they cancel each other out, resulting in zero net force.

Consider a Proton Traveling with a Velocity V in the Presence