Question

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)

• A. $2.0\times 10^{10}N$
• B. $2.0\times 10^{4}N$
• C. $2.0\times 10^{8}N$
• D. $2.0\times 10^{6}N$

Answer 1

Answer: (C)

Number of electrons, n
= $\frac{6\times 10^{23}}{63.5}\times 10\times \frac{1}{10^6}=\frac{6\times 10^{18}}{63.5}$
q = $\frac{6\times 10^{18}\times 1.6\times 10^{-19}}{63.5}$ C
or q = $1.5\times 10^{-2}$ C
F = $\frac{9\times 10^9\times 1.5\times 10^{-2}\times 1.5\times 10^{-2}}{\left(\frac{10}{100}\right)}N$
= $2.0\times 10^{8}N$