Final answer:
Charged particles controlled by a strong magnetic field are said to be perpendicular to the magnetic field, as the force on them is always perpendicular to their velocity and the magnetic field's direction.
Step-by-step explanation:
When a strong magnetic field controls the motion of charged particles, the particles are said to be perpendicular to the magnetic field. This comes from the basic principle of magnetism where the force exerted by the magnetic field on a moving charged particle is always perpendicular to the velocity of the particle and to the direction of the magnetic field itself. Hence, when a charged particle moves in a way that is governed by the magnetic field, its path bends at right angles to the field lines, forming a curved or circular motion.