Question

The forces between two small charged spheres having charges of $1\times {10}^{-7}C$ and $2\times {10}^{-7}C$ placed $20cm$ apart in air 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

The correct option is B $4.5\times {10}^{-3}N$

Here, $q_1=1\times {10}^{-7},q_2=2\times {10}^{-7},r=20cm=20\times {10}^{-2}m$

As $F=\frac{q_1{q}_2}{4\pi {\epsilon }_0{r}^2}=\frac{9\times {10}^9\times 1\times {10}^{-7}\times 2\times {10}^{-7}}{{(20\times {10}^{-2})}^2}=4.5\times {10}^{-3}N$