The force of attraction or repulsion between any two-point charges is directly proportional to the product of these charges and inversely proportional to the square of distance between them. The direction of force is always acting along the line joining these two-point charges. If \(F\) is a force acting on the charges \(q_1\) and \(q_2\text{,}\) and \(r\) is a distance between the two charges (see figure below) then from Coulumb’s law
Here, Coulomb’s constant, \(k=9\times 10^9 Nm^2/C^2\text{.}\) This law only works for two point charges at rest. Hence, the Coulomb’s law is also known as law of electrostatic force on
(a)unlike charges
(b)like charges
Figure5.1.2.Coulomb’s force
Example5.1.3.
If the distance between an electron and a proton in a hydrogen atom is \(0.53\times10^{-10} m\text{.}\) Find the electrostatic force acting between the electron and the proton.
Solution.
\begin{align*}
F \amp =k\frac{q_1q_2}{r^2}\\
or, \quad F \amp =9\times10^9\times\frac{(1.67\times10^{-19})\times (-1.67\times 10^{-19})}{(0.53\times10^{-10})^2}
\end{align*}
Answer.
\(\therefore F = -8.94\times10^{-8}N\text{.}\) Negative sign explains that the force is attractive in nature.
