Answer:
A) The electric and magnetic fields must be perpendicular to each other in that region
Explanation:
The proton does not experience any acceleration: this means that the net force acting on it is zero.
Therefore, this also means that the electric force and the magnetic force acting on the proton are balanced.
Let's remind that:
- The electric force acting on a positive charged particle has the same direction as the electric field:
F=qE
where F is the force, q is the charge, E is the electric field
- The magnetic force acting on a positive charged particle in motion is perpendicular to the direction of the magnetic field:
F=qv ∧ B
where q is the charge, v is the velocity of the particle, B is the magnetic field
Therefore, for the two forces to be along the same line (but in opposite directions), we must have that the electric field E and the magnetic field B are perpendicular to each other.
