A copper atom consists of copper nucleus surrounded by 29 electrons. The atomic weight of copper is `63.5 gmol^(-1)`. Let us now take two pieces of copper each weighing 10g. Let one electron from one piece be transferred to another for every 1000 atom in a piece.
(a) Find the magnitude of charge appearing on each piece.
(b) What will be the Coulomb force between the two pieces after the transfer of electrons if they are 10cm apart?

Explanation

In 1 mole copper (63.5 gm) there are `6xx10^(23)` atoms (`N_(A)=` Avagdro number `=6xx10^(23)` atoms)
Number of atoms `=(6xx10^(23)xx10)/63.5=9.45xx10^(22)`
For every 1000 atoms, 1 electron is transferred therefore total number of transferred electron is
`=(9.45xx10^(22))/1000=9.45xx10^(19)`
Therefore charge on one pice is e and on the other wil be `(9.45xx10^(19)e)`d
Force when they are kept 10 cm apart
`F=1/(4 pi epsilon_(0)) (q_(1)q_(2))/(r^(2))`
`=1/(4 pi epsilon_(0)) ((9.45xx10^(19))^(2)e^(2))/((10xx10^(-2))^(2))`
`=(9xx10^(9)xx(9.45xx10^(19))^(2)xx(1.6xx10^(-19))^(2))/((10xx10^(-2))^(2))`
`=2xx10^(14)N`