Acharged cloud system produces an electric field in the air near earth's surface. a particle of charge -2.0 × 10-9 c is acted on by a downward electrostatic force of 4.3 × 10-6 n when placed in this field. (a) what is the magnitude of the electric field? (b) what is the magnitude of the electrostatic force on a proton placed in this field? (c) what is the gravitational force on the proton? (d) what is the ratio of the electrostatic force to the gravitational force in this case?