A, B and C are three large, parallel conducting plates, placed horizontally. A and C are rigidly fixed and earthed. B is given some charge. Under electrostatic and gravitational forces, B may be

A and C are at zero potential.∴ Potential differences  VBA=VBCPlate  B will be in equilibrium only if  FA=mg+FC(FA and FC respectively are the forces of attraction on plate B  by plate A and C )This means FA>FC . This is possible only if electric field E=Vd in the gap  AB is more than that of the electric field in the gap BC .∵VBA=VBC∴dBA