Final answer:
All provided statements regarding the force on a charged particle in a magnetic field are valid. This force depends on charge, velocity, magnetic field strength, and acts at right angles to the particle's motion.
Step-by-step explanation:
The force on a charged particle in a magnetic field is determined by several factors (“e” is the correct response stating that all options are valid). The force depends on the charge of the particle (“a”), velocity of the particle (“b”), and strength of the external magnetic field (“c”). Additionally, it acts at right angles to the direction of the particle's motion (“d”).
When considering two charged particles like an electron and a proton moving with the same velocity in a magnetic field, their forces will differ due to differing charge magnitudes. However, since electron and proton have opposite charges, the force's direction will be opposite for each. The accelerations will also differ because acceleration depends on the particle's mass in addition to the force.
Increasing the magnitude of a uniform magnetic field does not necessarily increase the magnetic force on a charge unless the angle between the velocity and the magnetic field vectors is conducive to such an increase. Likewise, changing the magnetic field direction will change the force if it alters this angle.
If a charged particle moves in a straight line, one cannot conclude there is no magnetic field present; it's possible the motion is parallel to the field lines, or the magnetic field and electric force are balanced.