Question

Two small charged spheres having charges of $ \, 1\times 10^{- 7}C$ and $2\times 10^{- 7}C$ are placed $ \, 20$ $cm$ apart in air. The force between them is

• A. $ \, 4.5\times 10^{- 2}N$
• B. $4.5\times 10^{- 3}N$
• C. $5.4\times 10^{- 2}N$
• D. $5.4\times 10^{- 3}N$

Answer 1

Answer: (B)

Here, $q_{1}=1\times 10^{- 7}C, \, q_{2}=2\times 10^{- 7}C$
As $F=\frac{q_{1} q_{2}}{4 \pi \left(\epsilon \right)_{0} r^{2}}=\frac{9 \times \left(10\right)^{9} \times 1 \times \left(10\right)^{- 7} \times 2 \times \left(10\right)^{- 7}}{\left(20 \times \left(10\right)^{- 2}\right)^{2}}=4.5\times \left(10\right)^{- 3} \, N$