Final answer:
The trajectory of a proton traveling through a uniform magnetic field in the +x-direction will result in a magnetic force in the +y-direction, causing circular motion. If an electric field is present, it may either balance or combine with this force, altering the particle's trajectory. The net force from both fields will determine the proton's path.
Step-by-step explanation:
When a proton moves through a magnetic field, the resulting force on the proton is perpendicular to both its velocity and the magnetic field direction. This is due to the Lorentz force, which applies to charged particles moving through a magnetic field.
In the case where a proton moves in the -x-direction and encounters a uniform magnetic field pointing in the +x-direction, we can determine the direction of the magnetic force using the right-hand rule. If you point the fingers of your right hand in the direction of the proton's velocity and curl them towards the direction of the magnetic field, your thumb will point in the direction of the force. Since the proton has positive charge, the force will be directed in the direction your thumb points. Therefore, for a proton moving in the -x-direction and entering a magnetic field in the +x-direction, the resulting magnetic force will be in the +y-direction (out of the page), causing the proton to undergo circular motion.
Considering the interaction between the magnetic and electric fields, if an electric field is present and it is perpendicular to both the magnetic field and the motion of the proton, it can balance the magnetic force, resulting in a straight line trajectory for the proton. One must analyze the magnitude and direction of both the electric and magnetic fields to understand the net force on the proton.
If the proton is moving through a region where both magnetic and electric forces act, its trajectory will depend on the forces acting on it. These forces are the magnetic force, which can cause circular motion, and the electric force, which can either accelerate or decelerate the proton in a direction parallel to the electric field. The net force will determine the resulting trajectory of the proton, which could be a circle, spiral, or a straight line, depending on the relative strengths and directions of the electric and magnetic fields.