PHYSICS · Single correct · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
In an electrostatic precipitator, each dust particle of mass 2.0×10−12kg acquires a charge of −1.5×10−16C. The particle enters the region between two horizontal plates separated by 5.0cm; the upper plate is at +15kV and the lower plate is at Earth potential. Neglecting air drag, which statement correctly predicts the subsequent motion of the particle? (Take g=9.8ms−2.)
(a) It accelerates downward because the electric force (taken downward) exceeds its weight and quickly reaches the lower plate.
(b) It remains almost suspended between the plates since the electric force is calculated to balance its weight.
(c) It accelerates upward because the upward electric force is greater than its weight and therefore it reaches the upper plate.
(d) It moves downward with nearly the acceleration g because the electric force is much smaller than its weight.