Two copper balls, each weighing 10 g are kept in air 10 cm apart. If one electron from every `10^(6)` atoms is transferred from one ball to the other, the coulomb force between them is (atomic weight of copper is 63.5)

Options

A. `2.0xx10^(4)N`
B. `2.0xx10^(10)N`
C. `2.0xx10^(6)N`
D. `2.0xx10^(8)N`

Answer

D

Explanation

Number of atoms in 10 grams of copper
`=(6.023xx10^(23))/(63.5)xx10=9.485xx10^(22)`.
`therefore`Number of electrons transferred from one ball
to another`=(9.485xx10^(22))/(10^(6))=9.485xx10^(16)`
Now, the ball which looses electrons will be positively charged and the one which gains will be negatively charged.
`therefore`Charge on each ball`=Q=9.485xx10^(16)xxe`
[e=charge of an electron]
`=9.485xx10^(16)xx1.6xx10^(-19)`
`=9.485xx1.6xx10^(-3)C`.
`therefore`Coulomb force between them, `F=(1)/(4piepsi_(0))(QxxQ)/(r^(2))`
Here, `r=10cm=0.1m,(1)/(4piepsi_(0))=9xx10^(9)`
`thereforeF=(9xx10^(9)xx(9.485xx1.6xx10^(-3))^(2))/((0.1)^(2))`
`=2.072xx10^(8)Ncong2.0xx10^(8)N`.