Question

A copper atom consists of copper nucleus surrounded by `29` electrons. The atomic weight of copper is `63.5mol e^(-1)`. Let us now take two pieces of copper each weighing `10g`. Let us trandfer one elcetron from one piece to another for every `100` atoms in that piece. What will be the Coulomb force between the two pieces after the trandfer of electrons, if they are `1cm` apart? Avogadro number`= 6xx10^(23) mol e^(-1)`, charge on an electron `=-1.6xx10^(-19)C`.
A. `1.12xx10^(18)N`
B. `4.24xx10^(18)N`
C. `2.06xx10^(18)N`
D. `5.16xx10^(18)N`

Answer 1

Correct Answer - c
Here, Avogadro number, `N= 6xx10^(23) mol e^(-1)` and Atomic weight of copper, `A= 63.5 g mol e^(-1)`
Therefore, number of atoms in `10g` of copper.
`n=(N)/(A)xx10=(6xx10^(23)xx10)/(63.5)= 9.45xx10^(22)`
Since one electron per `100` atoms is trandferred from copper piece `A` to `B` the charge on copper piece `A`,
`q_(A)= +(n)/(100)xxe= +151.2C`
Obviously, charge on copper piece `B`,
`q_(B)= -151.2C`
Force between the two copper pieces,
`F= (1)/(4piepsilon_(0)).(q_(A)xxq_(B))/(r^(2))`
Setting `r= 1 cm= 0.01 m`, we get
`F= 2.06 xx10^(8)N` (attractive)