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}}{ \bigg( \frac{ 10 }{ 100 } \bigg) } N $
= $ 2.0 \times 10^8 \, N$