A charged particle moves through a region of space that has both a uniform electric field and a uniform magnetic field. In order for the particle to move through this region at a constant velocity,
A)The electric and magnetic fields must point in the same direction
B)The electric and magnetic fields must point in opposite directions.
C)The electric and magnetic fields must point in perpendicular directions.
D)The answer depends on the sign of the particle's electric charge.
The Attempt at a Solution
I was very confused by this one. I know that the electric field can cause a particle to speed up, but a magnetic field can only change the directional component of the velocity, but the speed doesn't change. I was thinking it would have to be B, but I really have no idea. Any help would be greatly appreciated.