Example – 1 Calculate protonic charge in 100 cc. of water.
Solution: 1 cc = 1 gm for water as density = 1000 kg/m3
Now no of atoms in 18 gm (atm weight) = 6.023 x 1023 and each molecule of H2O contains 10 proton (8 of oxygen + 2 of H2) so No. of proton in 100 gm water
Hence protonic charge = 3.3 × 1025 × 1.6 × 10-19 = 5.4 × 106 C
Example - 2 A copper sphere of mass 2.0 g contains about 2 x 1022 atoms. Atomic weight of copper is 64 and atomic number 29.
(i) How many electorns must be removed form the sphere to give it a charge of +2mC?
(ii) Determine the fraction of electrons removed.
(iii) Is there any change in mass of sphere when it is given positive charge?
Solution:
(i) Number of electrons to be removed 
(ii) Total number of electrons in the sphere = 29 x 2 x 1022 = 5.8 x 1023 Fraction of electrons removed  Thus 2.16 x 10-9% of electrons are to be removed to give the sphere a charge of 2mC
(iii) Yes mass decreases, when body is given a positive charge. Decrease of mass Δm= 9 x 10-31 x 1.25 x 1013 = 1.125 x 10-17 kg
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