Two copper balls, each weighing 10g are kept in air 10 cm apart. If one electron from every 106 atoms is transferred from one ball to the other, the coulomb force between them is (atomic weight of copper is 63.5)

Number of atoms in given mass =1063.5×6.02×1023=9.48×1022Transfer of electron between balls =9.48×1022106=9.48×1016Hence magnitude of charge gained by each ball. Q=9.48×1016×1.6×10−19=0.015CForce of attraction between the balls F=9×109×(0.015)2(0.1)2=2×108N