Electrostatics

What is the magnitude of electric field in which the electric force on a proton is equal in magnitude to its weight?

What must the charge (magnitude and nature) of a 1.45 gm particle be for it to remains stationary when placed in downward directed electric field of magnitude 650 N/C?

Two tiny conducting balls of identical mass m and charge q hang from non conducting thread each of length L. Derive an expression for the equilibrium separation 'x' between the balls assuming that the separation angle to be small.