Question

Two identical conducting small spheres are placed with their centres $0.3m$ apart. One is given a charge of $12.0nC$ and the other a charge of $-18.0nC$. Find the electric force exerted by one sphere on the other?

• A. $4.16\times {10}^{-5}N$
• B. $2.16\times {10}^{-5}N$
• C. $6.16\times {10}^{-5}N$
• D. $7.66\times {10}^{-5}N$

Answer 1

Answer: (B)

$2.16\times {10}^{-5}N$

Using Coulomb's law, $F=\frac{1}{4\pi {ϵ}_0}\frac{q_1{q}_2}{r^2}=(9\times {10}^9)\times \frac{(12\times {10}^{-9})(-18\times {10}^{-9})}{(0.3{)}^2}=-2.16\times {10}^{-5}N$ (negative sign for attractive force)