A free electron is placed between two large, parallel,nonconducting plates that are horizontal and 1.6 cm apart. One plate has a uniform positivecharge; the other has an equal amount of uniform negative charge.The force on the electron due to the electric field Evec between the plates balances the gravitational force on the electron. What is the magnitude and direction of the surface chargedensity on the plates? (Take upward to be positive.)