Final answer:
The uniform magnetic field will cause a charged particle to change its direction of motion by exerting a perpendicular force that does no work on the particle; thus, the speed remains constant. If the velocity is perpendicular to the field, the particle exhibits circular motion.
Step-by-step explanation:
When a charged particle enters a uniform magnetic field, it experiences a magnetic force. This force does not change the speed of the particle but instead acts perpendicular to both the particle's velocity and the magnetic field, altering the direction of motion. If the charged particle moves perpendicular to the field, it will follow a circular path due to this force providing the centripetal force necessary for circular motion. The magnetic field's effect is summarized by the Lorentz force equation, F = qvBsinθ, where 'q' is the charge of the particle, 'v' is its velocity, 'B' is the magnetic field strength, and 'θ' is the angle between the velocity and the magnetic field.
In the simplest case, if a charged particle, such as an electron, enters the field at a right angle, it will complete a circular path, where the magnetic force supplies the centripetal force necessary for this motion. In other cases, such as when a charged particle's velocity is not perpendicular to the field, its path will be a spiral or helix. Therefore, the correct answer to the question is that the magnetic field will cause the charged particle to change its direction of motion (1). The magnetic force itself, being perpendicular to the direction of motion, does no work on the particle, which means its speed does not increase (2) or decrease (3), and there is definitely an effect on the particle (4).