In a Millikan-type experiment, two horizontal parallel plates are 3.5 cm apart. A sphere of mass 4.2 Ă— 10^(-17) kg remains stationary when the potential difference between the plates is 5.00 V with the upper plate positive.
(a) Calculate the magnitude of charge on the sphere.
(b) How much excess or deficit of electrons does the sphere have? The charge of one electron is 1.602x10^(-19) C.
The electric force must be up to balance the downward force of gravity. The upper plate is positive and the bottom plate is negative. The sphere must be negatively charged to be repelled by the bottom plate and attracted to the upper plate.