In a laboratory apparatus that resembles the classic oil-drop experiment
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
In a laboratory apparatus that resembles the classic oil-drop experiment, a single microscopic oil drop of mass 1.0×10−14kg carries a net charge of +7.0×10−16C. The drop is located between two large, horizontal metal plates separated by 1.5cm. Air resistance on the drop is negligible.
(a) Calculate the magnitude of the potential difference that must be applied across the plates so the drop remains motionless.
(b) State which plate (upper or lower) must be at the higher potential to achieve levitation of the positively charged drop, and justify your answer.
(c) The applied potential difference is suddenly increased by 15 %. Determine the magnitude of the drop’s initial vertical acceleration immediately after the change.
(d) Suppose the plate separation were doubled while the potential difference found in part (a) is kept the same. Determine whether the drop would rise, fall, or remain motionless, and support your answer quantitatively.