1. The problem statement, all variables and given/known data A charged particle, passing through a certain region of space, has a velocity whose magnitude and direction remain constant. If it is known that the external magnetic field is zero everywhere in this region, can you conclude that the external electric field is also zero? 2. Relevant equations F=ma 3. The attempt at a solution Constant velocity means no acceleration is occurring. No accelerations means that the sum of the external forces acting on the mass is zero. That can mean either no forces are acting on it, or that forces are acting on it, but they exactly cancel each other. So in this case we have no magnetic field, but possibly an electric field. There might also be a gravitational field. So it is then possible that the gravitational force and the electric force exactly cancel each other out, so that the sum of the forces are zero. So then answer to the question then is "no". Would you agree with my reasoning?