Consider an electron in front of metallic surface at a distance d (treated as an infinite plane surface). Assume the force of attraction by the plate is given as 
Calculate work in taking the charge to an infinite distance from the plate. Taking d = 0.1nm, find the work done in electron volts. [Such a force law is not valid for d < 0.1nm].
In order to take a charge from a given distance ‘d’ from the plate to infinity, we would have to work against the electric force.
F is the attractive force = 
dx is infinitesimal displacement.
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