Parallel plates make a field that is constant in size and direction. That uniformity turns the motion of a charge into a problem you already know: projectile motion.
Between two parallel plates a distance d apart with potential difference V, the field is uniform with strength E = V / d. A charge fired across it has constant velocity along the plates and constant acceleration across them, so it follows a parabola.
Set the plate voltage and separation to control E = V/d, then watch a positive charge curve toward the negative plate. Widen the plates and the deflection shrinks.
The field, and so the force qE, is the same everywhere between the plates. The component of velocity parallel to the plates is unchanged while the perpendicular component grows at a steady rate, giving a parabolic path exactly like a projectile under gravity.
Four quick checks on E = V/d and the motion of a charge in a uniform field. Each correct answer earns XP and lights this skill on your star map.
Between parallel plates a distance d apart with a potential difference V, the field strength is:
The electric field between two parallel plates is:
A charged particle fired parallel to the plates follows:
Keeping the voltage fixed and doubling the plate separation makes the field:
E = V/d gives the field in volts per metre and applies only to the uniform field between parallel plates, not to a point charge. The path is parabolic because the parallel velocity stays constant while the perpendicular acceleration is constant, the same logic as projectile motion.
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