What is the electrostatic force between two small charged spheres having charges of $2 imes 10^{-7

Question

What is the electrostatic force between two small charged spheres having charges of $2 	imes 10^{-7}	ext{ C}$ and $3 	imes 10^{-7}	ext{ C}$ placed $30	ext{ cm}$ apart in air?

Professor PC Thomas Classes · Answer

Force $F = \frac{1}{4\pi\epsilon_0} \frac{q_1 q_2}{r^2} = \frac{9 	imes 10^9 	imes 2 	imes 10^{-7} 	imes 3 	imes 10^{-7}}{(0.3)^2} = \frac{54 	imes 10^{-5}}{0.09} = 6 	imes 10^{-3}	ext{ N}$. Because both charges are positive, the force is repulsive.