Two parallel metal plates separated by a distance 0.01 meters are charged in order to create a uniform electric field (4 x 104 N/C) between them, which points down (see figure). A small plastic ball (m = 0.009 kg) has a small charge Q on it and is located between the plates. The only forces on it are the forces due to gravity and to the electric field. The ball is not moving.
Note: An alpha particle is a bare helium-4 nucleus and has a mass about four times that of a proton. The mass of a proton is 2000 times the mass of an electron. The acceleration due to gravity g = 10 m/s2.The charge on a proton is 1.6 x 10–19 C.
Which is a distribution of charge which would create the desired electric field between the plates?